我最近上班又遇到一个小难题了，就是如题所述：ViewPager预加载的问题。相信用过ViewPager的人大抵都有遇到过这种情况，网上的解决办法也就那么几个，终于在我自己不断试验之下，完美解决了（禁止了）ViewPager的预加载。
好了，首先来说明一下，什么是ViewPager的预加载：ViewPager有一个 “预加载”的机制，默认会把ViewPager当前位置的左右相邻页面预先初始化（俗称的预加载），它的默认值是 1，这样做的好处就是ViewPager左右滑动会更加流畅。
可是我的情况很特殊，因为我 5 个Fragment里有一个Fragment是有SurfaceView的，这样造成的问题就是，我ViewPager滑动到其相邻页面时，含有SurfaceView的页面就会被预先初始化，然后SurfaceView就开始预览了，只是我们看不到而已。同样的，当我们从含有SurfaceView的页面滑倒其相邻的页面时，SurfaceView并不会回调其surfaceDestory方法。于是这给我造成了极大的困扰。
ok，下面言归正传，到底该怎么禁止ViewPager的这个预加载问题呢？
方案1：网上大多数说法是 懒加载，即让ViewPager预加载初始化UI，而具体一些数据，网络访问请求等延迟加载。这是靠Fragment里有一个setUserVisibleHint(boolean isVisibleToUser)的方法，我们可以在这个方法里做判断，当其True可见时（即切换到某一个具体Fragment）时才去加载数据，这样可以省流量。但这里并不满足我的需求，因为某一个Fragment并不会在ViewPager滑动到其相邻的Fragment时销毁。这个只可以解决部分人问题。
首先我们来深入了解下ViewPager的预加载机制：
上文提到过，ViewPager默认预加载的数量是1，这一点我们可以在ViewPager源码里看到。
DEFAULT_OFFSCREEN_PAGES 这里就定义了默认值是1， 所以网上 有种解决方案 说调用ViewPager的setOffscreenPageLimit(int limit)，来设置ViewPager预加载的数量，但是这里很明确的告诉你，这种方案是不可行的，如下图ViewPager源码：
我们可以看到，如果你调用该方法传进来的值小于1是无效的，会被强行的拽回1。而且DEFAULT_OFFSCREEN_PAGES 这个值是private的，子类继承ViewPager也是不可见的。
方案2：然后网上有第二种说法，自定义一个ViewPager，把原生ViewPager全拷过来，修改这个DEFAULT_OFFSCREEN_PAGES 值为0。对，就是这种解决方案！！但是！！
但是！！！但是什么呢？但是我试过，没用。为什么呢？接下来就是本文的重点了。
因为现在Android都6.0了，版本都老高了，其实android虽然每个版本都有v4包，但是这些v4包是有差异的。这就造成高版本v4包里的ViewPager，即使你Copy它，将其DEFAULT_OFFSCREEN_PAGES的值改为0，还是不起作用的，其中的逻辑变了。具体哪里变了导致无效我也没有继续研究了，毕竟公司不会花时间让我研究这些啊。偷笑
完美解决方案：ok，所以关于禁止ViewPager预加载的完美解决方案就是，使用低版本v4包里的ViewPager，完全copy一份，将其中的DEFAULT_OFFSCREEN_PAGES值改为0即可。博主亲测 API 14 即 Android 4.0的v4包里ViewPager 有效。
当然，谷歌既然有这么一种ViewPager的机制肯定有它的道理，所以一般还是预加载的好。
最后，因为低版本的源码越来越少的人会去下载，这里直接把这个禁止了预加载的ViewPager贴上来，需要的人就拿去吧。copy就能用了。
package com.plumcot.usb.view;/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */import android.content.Context;import android.database.DataSetObserver;import android.graphics.Canvas;import android.graphics.Rect;import android.graphics.drawable.Drawable;import android.os.Parcel;import android.os.Parcelable;import android.os.SystemClock;import android.support.v4.os.ParcelableCompat;import android.support.v4.os.ParcelableCompatCreatorCallbacks;import android.support.v4.view.KeyEventCompat;import android.support.v4.view.MotionEventCompat;import android.support.v4.view.PagerAdapter;import android.support.v4.view.VelocityTrackerCompat;import android.support.v4.view.ViewCompat;import android.support.v4.view.ViewConfigurationCompat;import android.support.v4.widget.EdgeEffectCompat;import android.util.AttributeSet;import android.util.Log;import android.view.FocusFinder;import android.view.KeyEvent;import android.view.MotionEvent;import android.view.SoundEffectConstants;import android.view.VelocityTracker;import android.view.View;import android.view.ViewConfiguration;import android.view.ViewGroup;import android.view.ViewParent;import android.view.accessibility.AccessibilityEvent;import android.view.animation.Interpolator;import android.widget.Scroller;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;/** * Layout manager that allows the user to flip left and right * through pages of data. You supply an implementation of a * {@link android.support.v4.view.PagerAdapter} to generate the pages that the view shows. * * <p>Note this class is currently under early design and * development. The API will likely change in later updates of * the compatibility library, requiring changes to the source code * of apps when they are compiled against the newer version.</p> */public class NoPreloadViewPager extends ViewGroup { private static final String TAG = "<span style="font-family:Arial, Helvetica, sans-serif;">NoPreLoadViewPager</span>"; private static final boolean DEBUG = false; private static final boolean USE_CACHE = false; private static final int DEFAULT_OFFSCREEN_PAGES = 0;//默认是1 private static final int MAX_SETTLE_DURATION = 600; // ms static class ItemInfo { Object object; int position; boolean scrolling; } private static final Comparator<ItemInfo> COMPARATOR = new Comparator<ItemInfo>(){ @Override public int compare(ItemInfo lhs, ItemInfo rhs) { return lhs.position - rhs.position; }}; private static final Interpolator sInterpolator = new Interpolator() { public float getInterpolation(float t) { // _o(t) = t * t * ((tension + 1) * t + tension) // o(t) = _o(t - 1) + 1 t -= 1.0f; return t * t * t + 1.0f; } }; private final ArrayList<ItemInfo> mItems = new ArrayList<ItemInfo>(); private PagerAdapter mAdapter; private int mCurItem; // Index of currently displayed page. private int mRestoredCurItem = -1; private Parcelable mRestoredAdapterState = null; private ClassLoader mRestoredClassLoader = null; private Scroller mScroller; private PagerObserver mObserver; private int mPageMargin; private Drawable mMarginDrawable; private int mChildWidthMeasureSpec; private int mChildHeightMeasureSpec; private boolean mInLayout; private boolean mScrollingCacheEnabled; private boolean mPopulatePending; private boolean mScrolling; private int mOffscreenPageLimit = DEFAULT_OFFSCREEN_PAGES; private boolean mIsBeingDragged; private boolean mIsUnableToDrag; private int mTouchSlop; private float mInitialMotionX; /** * Position of the last motion event. */ private float mLastMotionX; private float mLastMotionY; /** * ID of the active pointer. This is used to retain consistency during * drags/flings if multiple pointers are used. */ private int mActivePointerId = INVALID_POINTER; /** * Sentinel value for no current active pointer. * Used by {@link #mActivePointerId}. */ private static final int INVALID_POINTER = -1; /** * Determines speed during touch scrolling */ private VelocityTracker mVelocityTracker; private int mMinimumVelocity; private int mMaximumVelocity; private float mBaseLineFlingVelocity; private float mFlingVelocityInfluence; private boolean mFakeDragging; private long mFakeDragBeginTime; private EdgeEffectCompat mLeftEdge; private EdgeEffectCompat mRightEdge; private boolean mFirstLayout = true; private OnPageChangeListener mOnPageChangeListener; /** * Indicates that the pager is in an idle, settled state. The current page * is fully in view and no animation is in progress. */ public static final int SCROLL_STATE_IDLE = 0; /** * Indicates that the pager is currently being dragged by the user. */ public static final int SCROLL_STATE_DRAGGING = 1; /** * Indicates that the pager is in the process of settling to a final position. */ public static final int SCROLL_STATE_SETTLING = 2; private int mScrollState = SCROLL_STATE_IDLE; /** * Callback interface for responding to changing state of the selected page. */ public interface OnPageChangeListener { /** * This method will be invoked when the current page is scrolled, either as part * of a programmatically initiated smooth scroll or a user initiated touch scroll. * * @param position Position index of the first page currently being displayed. * Page position+1 will be visible if positionOffset is nonzero. * @param positionOffset Value from [0, 1) indicating the offset from the page at position. * @param positionOffsetPixels Value in pixels indicating the offset from position. */ public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels); /** * This method will be invoked when a new page becomes selected. Animation is not * necessarily complete. * * @param position Position index of the new selected page. */ public void onPageSelected(int position); /** * Called when the scroll state changes. Useful for discovering when the user * begins dragging, when the pager is automatically settling to the current page, * or when it is fully stopped/idle. * * @param state The new scroll state. * @see android.support.v4.view.ViewPager#SCROLL_STATE_IDLE * @see android.support.v4.view.ViewPager#SCROLL_STATE_DRAGGING * @see android.support.v4.view.ViewPager#SCROLL_STATE_SETTLING */ public void onPageScrollStateChanged(int state); } /** * Simple implementation of the {@link android.support.v4.view.LazyViewPager.OnPageChangeListener} interface with stub * implementations of each method. Extend this if you do not intend to override * every method of {@link android.support.v4.view.LazyViewPager.OnPageChangeListener}. */ public static class SimpleOnPageChangeListener implements OnPageChangeListener { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { // This space for rent } @Override public void onPageSelected(int position) { // This space for rent } @Override public void onPageScrollStateChanged(int state) { // This space for rent } } public NoPreloadViewPager(Context context) { super(context); initViewPager(); } public NoPreloadViewPager(Context context, AttributeSet attrs) { super(context, attrs); initViewPager(); } void initViewPager() { setWillNotDraw(false); setDescendantFocusability(FOCUS_AFTER_DESCENDANTS); setFocusable(true); final Context context = getContext(); mScroller = new Scroller(context, sInterpolator); final ViewConfiguration configuration = ViewConfiguration.get(context); mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration); mMinimumVelocity = configuration.getScaledMinimumFlingVelocity(); mMaximumVelocity = configuration.getScaledMaximumFlingVelocity(); mLeftEdge = new EdgeEffectCompat(context); mRightEdge = new EdgeEffectCompat(context); float density = context.getResources().getDisplayMetrics().density; mBaseLineFlingVelocity = 2500.0f * density; mFlingVelocityInfluence = 0.4f; } private void setScrollState(int newState) { if (mScrollState == newState) { return; } mScrollState = newState; if (mOnPageChangeListener != null) { mOnPageChangeListener.onPageScrollStateChanged(newState); } } public void setAdapter(PagerAdapter adapter) { if (mAdapter != null) {// mAdapter.unregisterDataSetObserver(mObserver); mAdapter.startUpdate(this); for (int i = 0; i < mItems.size(); i++) { final ItemInfo ii = mItems.get(i); mAdapter.destroyItem(this, ii.position, ii.object); } mAdapter.finishUpdate(this); mItems.clear(); removeAllViews(); mCurItem = 0; scrollTo(0, 0); } mAdapter = adapter; if (mAdapter != null) { if (mObserver == null) { mObserver = new PagerObserver(); }// mAdapter.registerDataSetObserver(mObserver); mPopulatePending = false; if (mRestoredCurItem >= 0) { mAdapter.restoreState(mRestoredAdapterState, mRestoredClassLoader); setCurrentItemInternal(mRestoredCurItem, false, true); mRestoredCurItem = -1; mRestoredAdapterState = null; mRestoredClassLoader = null; } else { populate(); } } } public PagerAdapter getAdapter() { return mAdapter; } /** * Set the currently selected page. If the ViewPager has already been through its first * layout there will be a smooth animated transition between the current item and the * specified item. * * @param item Item index to select */ public void setCurrentItem(int item) { mPopulatePending = false; setCurrentItemInternal(item, !mFirstLayout, false); } /** * Set the currently selected page. * * @param item Item index to select * @param smoothScroll True to smoothly scroll to the new item, false to transition immediately */ public void setCurrentItem(int item, boolean smoothScroll) { mPopulatePending = false; setCurrentItemInternal(item, smoothScroll, false); } public int getCurrentItem() { return mCurItem; } void setCurrentItemInternal(int item, boolean smoothScroll, boolean always) { setCurrentItemInternal(item, smoothScroll, always, 0); } void setCurrentItemInternal(int item, boolean smoothScroll, boolean always, int velocity) { if (mAdapter == null || mAdapter.getCount() <= 0) { setScrollingCacheEnabled(false); return; } if (!always && mCurItem == item && mItems.size() != 0) { setScrollingCacheEnabled(false); return; } if (item < 0) { item = 0; } else if (item >= mAdapter.getCount()) { item = mAdapter.getCount() - 1; } final int pageLimit = mOffscreenPageLimit; if (item > (mCurItem + pageLimit) || item < (mCurItem - pageLimit)) { // We are doing a jump by more than one page. To avoid // glitches, we want to keep all current pages in the view // until the scroll ends. for (int i=0; i<mItems.size(); i++) { mItems.get(i).scrolling = true; } } final boolean dispatchSelected = mCurItem != item; mCurItem = item; populate(); final int destX = (getWidth() + mPageMargin) * item; if (smoothScroll) { smoothScrollTo(destX, 0, velocity); if (dispatchSelected && mOnPageChangeListener != null) { mOnPageChangeListener.onPageSelected(item); } } else { if (dispatchSelected && mOnPageChangeListener != null) { mOnPageChangeListener.onPageSelected(item); } completeScroll(); scrollTo(destX, 0); } } public void setOnPageChangeListener(OnPageChangeListener listener) { mOnPageChangeListener = listener; } /** * Returns the number of pages that will be retained to either side of the * current page in the view hierarchy in an idle state. Defaults to 1. * * @return How many pages will be kept offscreen on either side * @see #setOffscreenPageLimit(int) */ public int getOffscreenPageLimit() { return mOffscreenPageLimit; } /** * Set the number of pages that should be retained to either side of the * current page in the view hierarchy in an idle state. Pages beyond this * limit will be recreated from the adapter when needed. * * <p>This is offered as an optimization. If you know in advance the number * of pages you will need to support or have lazy-loading mechanisms in place * on your pages, tweaking this setting can have benefits in perceived smoothness * of paging animations and interaction. If you have a small number of pages (3-4) * that you can keep active all at once, less time will be spent in layout for * newly created view subtrees as the user pages back and forth.</p> * * <p>You should keep this limit low, especially if your pages have complex layouts. * This setting defaults to 1.</p> * * @param limit How many pages will be kept offscreen in an idle state. */ public void setOffscreenPageLimit(int limit) { if (limit < DEFAULT_OFFSCREEN_PAGES) { Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to " + DEFAULT_OFFSCREEN_PAGES); limit = DEFAULT_OFFSCREEN_PAGES; } if (limit != mOffscreenPageLimit) { mOffscreenPageLimit = limit; populate(); } } /** * Set the margin between pages. * * @param marginPixels Distance between adjacent pages in pixels * @see #getPageMargin() * @see #setPageMarginDrawable(android.graphics.drawable.Drawable) * @see #setPageMarginDrawable(int) */ public void setPageMargin(int marginPixels) { final int oldMargin = mPageMargin; mPageMargin = marginPixels; final int width = getWidth(); recomputeScrollPosition(width, width, marginPixels, oldMargin); requestLayout(); } /** * Return the margin between pages. * * @return The size of the margin in pixels */ public int getPageMargin() { return mPageMargin; } /** * Set a drawable that will be used to fill the margin between pages. * * @param d Drawable to display between pages */ public void setPageMarginDrawable(Drawable d) { mMarginDrawable = d; if (d != null) refreshDrawableState(); setWillNotDraw(d == null); invalidate(); } /** * Set a drawable that will be used to fill the margin between pages. * * @param resId Resource ID of a drawable to display between pages */ public void setPageMarginDrawable(int resId) { setPageMarginDrawable(getContext().getResources().getDrawable(resId)); } @Override protected boolean verifyDrawable(Drawable who) { return super.verifyDrawable(who) || who == mMarginDrawable; } @Override protected void drawableStateChanged() { super.drawableStateChanged(); final Drawable d = mMarginDrawable; if (d != null && d.isStateful()) { d.setState(getDrawableState()); } } // We want the duration of the page snap animation to be influenced by the distance that // the screen has to travel, however, we don't want this duration to be effected in a // purely linear fashion. Instead, we use this method to moderate the effect that the distance // of travel has on the overall snap duration. float distanceInfluenceForSnapDuration(float f) { f -= 0.5f; // center the values about 0. f *= 0.3f * Math.PI / 2.0f; return (float) Math.sin(f); } /** * Like {@link android.view.View#scrollBy}, but scroll smoothly instead of immediately. * * @param x the number of pixels to scroll by on the X axis * @param y the number of pixels to scroll by on the Y axis */ void smoothScrollTo(int x, int y) { smoothScrollTo(x, y, 0); } /** * Like {@link android.view.View#scrollBy}, but scroll smoothly instead of immediately. * * @param x the number of pixels to scroll by on the X axis * @param y the number of pixels to scroll by on the Y axis * @param velocity the velocity associated with a fling, if applicable. (0 otherwise) */ void smoothScrollTo(int x, int y, int velocity) { if (getChildCount() == 0) { // Nothing to do. setScrollingCacheEnabled(false); return; } int sx = getScrollX(); int sy = getScrollY(); int dx = x - sx; int dy = y - sy; if (dx == 0 && dy == 0) { completeScroll(); setScrollState(SCROLL_STATE_IDLE); return; } setScrollingCacheEnabled(true); mScrolling = true; setScrollState(SCROLL_STATE_SETTLING); final float pageDelta = (float) Math.abs(dx) / (getWidth() + mPageMargin); int duration = (int) (pageDelta * 100); velocity = Math.abs(velocity); if (velocity > 0) { duration += (duration / (velocity / mBaseLineFlingVelocity)) * mFlingVelocityInfluence; } else { duration += 100; } duration = Math.min(duration, MAX_SETTLE_DURATION); mScroller.startScroll(sx, sy, dx, dy, duration); invalidate(); } void addNewItem(int position, int index) { ItemInfo ii = new ItemInfo(); ii.position = position; ii.object = mAdapter.instantiateItem(this, position); if (index < 0) { mItems.add(ii); } else { mItems.add(index, ii); } } void dataSetChanged() { // This method only gets called if our observer is attached, so mAdapter is non-null. boolean needPopulate = mItems.size() < 3 && mItems.size() < mAdapter.getCount(); int newCurrItem = -1; for (int i = 0; i < mItems.size(); i++) { final ItemInfo ii = mItems.get(i); final int newPos = mAdapter.getItemPosition(ii.object); if (newPos == PagerAdapter.POSITION_UNCHANGED) { continue; } if (newPos == PagerAdapter.POSITION_NONE) { mItems.remove(i); i--; mAdapter.destroyItem(this, ii.position, ii.object); needPopulate = true; if (mCurItem == ii.position) { // Keep the current item in the valid range newCurrItem = Math.max(0, Math.min(mCurItem, mAdapter.getCount() - 1)); } continue; } if (ii.position != newPos) { if (ii.position == mCurItem) { // Our current item changed position. Follow it. newCurrItem = newPos; } ii.position = newPos; needPopulate = true; } } Collections.sort(mItems, COMPARATOR); if (newCurrItem >= 0) { // TODO This currently causes a jump. setCurrentItemInternal(newCurrItem, false, true); needPopulate = true; } if (needPopulate) { populate(); requestLayout(); } } void populate() { if (mAdapter == null) { return; } // Bail now if we are waiting to populate. This is to hold off // on creating views from the time the user releases their finger to // fling to a new position until we have finished the scroll to // that position, avoiding glitches from happening at that point. if (mPopulatePending) { if (DEBUG) Log.i(TAG, "populate is pending, skipping for now..."); return; } // Also, don't populate until we are attached to a window. This is to // avoid trying to populate before we have restored our view hierarchy // state and conflicting with what is restored. if (getWindowToken() == null) { return; } mAdapter.startUpdate(this); final int pageLimit = mOffscreenPageLimit; final int startPos = Math.max(0, mCurItem - pageLimit); final int N = mAdapter.getCount(); final int endPos = Math.min(N-1, mCurItem + pageLimit); if (DEBUG) Log.v(TAG, "populating: startPos=" + startPos + " endPos=" + endPos); // Add and remove pages in the existing list. int lastPos = -1; for (int i=0; i<mItems.size(); i++) { ItemInfo ii = mItems.get(i); if ((ii.position < startPos || ii.position > endPos) && !ii.scrolling) { if (DEBUG) Log.i(TAG, "removing: " + ii.position + " @ " + i); mItems.remove(i); i--; mAdapter.destroyItem(this, ii.position, ii.object); } else if (lastPos < endPos && ii.position > startPos) { // The next item is outside of our range, but we have a gap // between it and the last item where we want to have a page // shown. Fill in the gap. lastPos++; if (lastPos < startPos) { lastPos = startPos; } while (lastPos <= endPos && lastPos < ii.position) { if (DEBUG) Log.i(TAG, "inserting: " + lastPos + " @ " + i); addNewItem(lastPos, i); lastPos++; i++; } } lastPos = ii.position; } // Add any new pages we need at the end. lastPos = mItems.size() > 0 ? mItems.get(mItems.size()-1).position : -1; if (lastPos < endPos) { lastPos++; lastPos = lastPos > startPos ? lastPos : startPos; while (lastPos <= endPos) { if (DEBUG) Log.i(TAG, "appending: " + lastPos); addNewItem(lastPos, -1); lastPos++; } } if (DEBUG) { Log.i(TAG, "Current page list:"); for (int i=0; i<mItems.size(); i++) { Log.i(TAG, "#" + i + ": page " + mItems.get(i).position); } } ItemInfo curItem = null; for (int i=0; i<mItems.size(); i++) { if (mItems.get(i).position == mCurItem) { curItem = mItems.get(i); break; } } mAdapter.setPrimaryItem(this, mCurItem, curItem != null ? curItem.object : null); mAdapter.finishUpdate(this); if (hasFocus()) { View currentFocused = findFocus(); ItemInfo ii = currentFocused != null ? infoForAnyChild(currentFocused) : null; if (ii == null || ii.position != mCurItem) { for (int i=0; i<getChildCount(); i++) { View child = getChildAt(i); ii = infoForChild(child); if (ii != null && ii.position == mCurItem) { if (child.requestFocus(FOCUS_FORWARD)) { break; } } } } } } public static class SavedState extends BaseSavedState { int position; Parcelable adapterState; ClassLoader loader; public SavedState(Parcelable superState) { super(superState); } @Override public void writeToParcel(Parcel out, int flags) { super.writeToParcel(out, flags); out.writeInt(position); out.writeParcelable(adapterState, flags); } @Override public String toString() { return "FragmentPager.SavedState{" + Integer.toHexString(System.identityHashCode(this)) + " position=" + position + "}"; } public static final Creator<SavedState> CREATOR = ParcelableCompat.newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() { @Override public SavedState createFromParcel(Parcel in, ClassLoader loader) { return new SavedState(in, loader); } @Override public SavedState[] newArray(int size) { return new SavedState[size]; } }); SavedState(Parcel in, ClassLoader loader) { super(in); if (loader == null) { loader = getClass().getClassLoader(); } position = in.readInt(); adapterState = in.readParcelable(loader); this.loader = loader; } } @Override public Parcelable onSaveInstanceState() { Parcelable superState = super.onSaveInstanceState(); SavedState ss = new SavedState(superState); ss.position = mCurItem; if (mAdapter != null) { ss.adapterState = mAdapter.saveState(); } return ss; } @Override public void onRestoreInstanceState(Parcelable state) { if (!(state instanceof SavedState)) { super.onRestoreInstanceState(state); return; } SavedState ss = (SavedState)state; super.onRestoreInstanceState(ss.getSuperState()); if (mAdapter != null) { mAdapter.restoreState(ss.adapterState, ss.loader); setCurrentItemInternal(ss.position, false, true); } else { mRestoredCurItem = ss.position; mRestoredAdapterState = ss.adapterState; mRestoredClassLoader = ss.loader; } } @Override public void addView(View child, int index, LayoutParams params) { if (mInLayout) { addViewInLayout(child, index, params); child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec); } else { super.addView(child, index, params); } if (USE_CACHE) { if (child.getVisibility() != GONE) { child.setDrawingCacheEnabled(mScrollingCacheEnabled); } else { child.setDrawingCacheEnabled(false); } } } ItemInfo infoForChild(View child) { for (int i=0; i<mItems.size(); i++) { ItemInfo ii = mItems.get(i); if (mAdapter.isViewFromObject(child, ii.object)) { return ii; } } return null; } ItemInfo infoForAnyChild(View child) { ViewParent parent; while ((parent=child.getParent()) != this) { if (parent == null || !(parent instanceof View)) { return null; } child = (View)parent; } return infoForChild(child); } @Override protected void onAttachedToWindow() { super.onAttachedToWindow(); mFirstLayout = true; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { // For simple implementation, or internal size is always 0. // We depend on the container to specify the layout size of // our view. We can't really know what it is since we will be // adding and removing different arbitrary views and do not // want the layout to change as this happens. setMeasuredDimension(getDefaultSize(0, widthMeasureSpec), getDefaultSize(0, heightMeasureSpec)); // Children are just made to fill our space. mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() - getPaddingLeft() - getPaddingRight(), MeasureSpec.EXACTLY); mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() - getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY); // Make sure we have created all fragments that we need to have shown. mInLayout = true; populate(); mInLayout = false; // Make sure all children have been properly measured. final int size = getChildCount(); for (int i = 0; i < size; ++i) { final View child = getChildAt(i); if (child.getVisibility() != GONE) { if (DEBUG) Log.v(TAG, "Measuring #" + i + " " + child + ": " + mChildWidthMeasureSpec); child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec); } } } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); // Make sure scroll position is set correctly. if (w != oldw) { recomputeScrollPosition(w, oldw, mPageMargin, mPageMargin); } } private void recomputeScrollPosition(int width, int oldWidth, int margin, int oldMargin) { final int widthWithMargin = width + margin; if (oldWidth > 0) { final int oldScrollPos = getScrollX(); final int oldwwm = oldWidth + oldMargin; final int oldScrollItem = oldScrollPos / oldwwm; final float scrollOffset = (float) (oldScrollPos % oldwwm) / oldwwm; final int scrollPos = (int) ((oldScrollItem + scrollOffset) * widthWithMargin); scrollTo(scrollPos, getScrollY()); if (!mScroller.isFinished()) { // We now return to your regularly scheduled scroll, already in progress. final int newDuration = mScroller.getDuration() - mScroller.timePassed(); mScroller.startScroll(scrollPos, 0, mCurItem * widthWithMargin, 0, newDuration); } } else { int scrollPos = mCurItem * widthWithMargin; if (scrollPos != getScrollX()) { completeScroll(); scrollTo(scrollPos, getScrollY()); } } } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { mInLayout = true; populate(); mInLayout = false; final int count = getChildCount(); final int width = r-l; for (int i = 0; i < count; i++) { View child = getChildAt(i); ItemInfo ii; if (child.getVisibility() != GONE && (ii=infoForChild(child)) != null) { int loff = (width + mPageMargin) * ii.position; int childLeft = getPaddingLeft() + loff; int childTop = getPaddingTop(); if (DEBUG) Log.v(TAG, "Positioning #" + i + " " + child + " f=" + ii.object + ":" + childLeft + "," + childTop + " " + child.getMeasuredWidth() + "x" + child.getMeasuredHeight()); child.layout(childLeft, childTop, childLeft + child.getMeasuredWidth(), childTop + child.getMeasuredHeight()); } } mFirstLayout = false; } @Override public void computeScroll() { if (DEBUG) Log.i(TAG, "computeScroll: finished=" + mScroller.isFinished()); if (!mScroller.isFinished()) { if (mScroller.computeScrollOffset()) { if (DEBUG) Log.i(TAG, "computeScroll: still scrolling"); int oldX = getScrollX(); int oldY = getScrollY(); int x = mScroller.getCurrX(); int y = mScroller.getCurrY(); if (oldX != x || oldY != y) { scrollTo(x, y); } if (mOnPageChangeListener != null) { final int widthWithMargin = getWidth() + mPageMargin; final int position = x / widthWithMargin; final int offsetPixels = x % widthWithMargin; final float offset = (float) offsetPixels / widthWithMargin; mOnPageChangeListener.onPageScrolled(position, offset, offsetPixels); } // Keep on drawing until the animation has finished. invalidate(); return; } } // Done with scroll, clean up state. completeScroll(); } private void completeScroll() { boolean needPopulate = mScrolling; if (needPopulate) { // Done with scroll, no longer want to cache view drawing. setScrollingCacheEnabled(false); mScroller.abortAnimation(); int oldX = getScrollX(); int oldY = getScrollY(); int x = mScroller.getCurrX(); int y = mScroller.getCurrY(); if (oldX != x || oldY != y) { scrollTo(x, y); } setScrollState(SCROLL_STATE_IDLE); } mPopulatePending = false; mScrolling = false; for (int i=0; i<mItems.size(); i++) { ItemInfo ii = mItems.get(i); if (ii.scrolling) { needPopulate = true; ii.scrolling = false; } } if (needPopulate) { populate(); } } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { /* * This method JUST determines whether we want to intercept the motion. * If we return true, onMotionEvent will be called and we do the actual * scrolling there. */ final int action = ev.getAction() & MotionEventCompat.ACTION_MASK; // Always take care of the touch gesture being complete. if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) { // Release the drag. if (DEBUG) Log.v(TAG, "Intercept done!"); mIsBeingDragged = false; mIsUnableToDrag = false; mActivePointerId = INVALID_POINTER; return false; } // Nothing more to do here if we have decided whether or not we // are dragging. if (action != MotionEvent.ACTION_DOWN) { if (mIsBeingDragged) { if (DEBUG) Log.v(TAG, "Intercept returning true!"); return true; } if (mIsUnableToDrag) { if (DEBUG) Log.v(TAG, "Intercept returning false!"); return false; } } switch (action) { case MotionEvent.ACTION_MOVE: { /* * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check * whether the user has moved far enough from his original down touch. */ /* * Locally do absolute value. mLastMotionY is set to the y value * of the down event. */ final int activePointerId = mActivePointerId; if (activePointerId == INVALID_POINTER) { // If we don't have a valid id, the touch down wasn't on content. break; } final int pointerIndex = MotionEventCompat.findPointerIndex(ev, activePointerId); final float x = MotionEventCompat.getX(ev, pointerIndex); final float dx = x - mLastMotionX; final float xDiff = Math.abs(dx); final float y = MotionEventCompat.getY(ev, pointerIndex); final float yDiff = Math.abs(y - mLastMotionY); final int scrollX = getScrollX(); final boolean atEdge = (dx > 0 && scrollX == 0) || (dx < 0 && mAdapter != null && scrollX >= (mAdapter.getCount() - 1) * getWidth() - 1); if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff); if (canScroll(this, false, (int) dx, (int) x, (int) y)) { // Nested view has scrollable area under this point. Let it be handled there. mInitialMotionX = mLastMotionX = x; mLastMotionY = y; return false; } if (xDiff > mTouchSlop && xDiff > yDiff) { if (DEBUG) Log.v(TAG, "Starting drag!"); mIsBeingDragged = true; setScrollState(SCROLL_STATE_DRAGGING); mLastMotionX = x; setScrollingCacheEnabled(true); } else { if (yDiff > mTouchSlop) { // The finger has moved enough in the vertical // direction to be counted as a drag... abort // any attempt to drag horizontally, to work correctly // with children that have scrolling containers. if (DEBUG) Log.v(TAG, "Starting unable to drag!"); mIsUnableToDrag = true; } } break; } case MotionEvent.ACTION_DOWN: { /* * Remember location of down touch. * ACTION_DOWN always refers to pointer index 0. */ mLastMotionX = mInitialMotionX = ev.getX(); mLastMotionY = ev.getY(); mActivePointerId = MotionEventCompat.getPointerId(ev, 0); if (mScrollState == SCROLL_STATE_SETTLING) { // Let the user 'catch' the pager as it animates. mIsBeingDragged = true; mIsUnableToDrag = false; setScrollState(SCROLL_STATE_DRAGGING); } else { completeScroll(); mIsBeingDragged = false; mIsUnableToDrag = false; } if (DEBUG) Log.v(TAG, "Down at " + mLastMotionX + "," + mLastMotionY + " mIsBeingDragged=" + mIsBeingDragged + "mIsUnableToDrag=" + mIsUnableToDrag); break; } case MotionEventCompat.ACTION_POINTER_UP: onSecondaryPointerUp(ev); break; } /* * The only time we want to intercept motion events is if we are in the * drag mode. */ return mIsBeingDragged; } @Override public boolean onTouchEvent(MotionEvent ev) { if (mFakeDragging) { // A fake drag is in progress already, ignore this real one // but still eat the touch events. // (It is likely that the user is multi-touching the screen.) return true; } if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) { // Don't handle edge touches immediately -- they may actually belong to one of our // descendants. return false; } if (mAdapter == null || mAdapter.getCount() == 0) { // Nothing to present or scroll; nothing to touch. return false; } if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(ev); final int action = ev.getAction(); boolean needsInvalidate = false; switch (action & MotionEventCompat.ACTION_MASK) { case MotionEvent.ACTION_DOWN: { /* * If being flinged and user touches, stop the fling. isFinished * will be false if being flinged. */ completeScroll(); // Remember where the motion event started mLastMotionX = mInitialMotionX = ev.getX(); mActivePointerId = MotionEventCompat.getPointerId(ev, 0); break; } case MotionEvent.ACTION_MOVE: if (!mIsBeingDragged) { final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId); final float x = MotionEventCompat.getX(ev, pointerIndex); final float xDiff = Math.abs(x - mLastMotionX); final float y = MotionEventCompat.getY(ev, pointerIndex); final float yDiff = Math.abs(y - mLastMotionY); if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff); if (xDiff > mTouchSlop && xDiff > yDiff) { if (DEBUG) Log.v(TAG, "Starting drag!"); mIsBeingDragged = true; mLastMotionX = x; setScrollState(SCROLL_STATE_DRAGGING); setScrollingCacheEnabled(true); } } if (mIsBeingDragged) { // Scroll to follow the motion event final int activePointerIndex = MotionEventCompat.findPointerIndex( ev, mActivePointerId); final float x = MotionEventCompat.getX(ev, activePointerIndex); final float deltaX = mLastMotionX - x; mLastMotionX = x; float oldScrollX = getScrollX(); float scrollX = oldScrollX + deltaX; final int width = getWidth(); final int widthWithMargin = width + mPageMargin; final int lastItemIndex = mAdapter.getCount() - 1; final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin); final float rightBound = Math.min(mCurItem + 1, lastItemIndex) * widthWithMargin; if (scrollX < leftBound) { if (leftBound == 0) { float over = -scrollX; needsInvalidate = mLeftEdge.onPull(over / width); } scrollX = leftBound; } else if (scrollX > rightBound) { if (rightBound == lastItemIndex * widthWithMargin) { float over = scrollX - rightBound; needsInvalidate = mRightEdge.onPull(over / width); } scrollX = rightBound; } // Don't lose the rounded component mLastMotionX += scrollX - (int) scrollX; scrollTo((int) scrollX, getScrollY()); if (mOnPageChangeListener != null) { final int position = (int) scrollX / widthWithMargin; final int positionOffsetPixels = (int) scrollX % widthWithMargin; final float positionOffset = (float) positionOffsetPixels / widthWithMargin; mOnPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels); } } break; case MotionEvent.ACTION_UP: if (mIsBeingDragged) { final VelocityTracker velocityTracker = mVelocityTracker; velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity); int initialVelocity = (int) VelocityTrackerCompat.getXVelocity( velocityTracker, mActivePointerId); mPopulatePending = true; final int widthWithMargin = getWidth() + mPageMargin; final int scrollX = getScrollX(); final int currentPage = scrollX / widthWithMargin; int nextPage = initialVelocity > 0 ? currentPage : currentPage + 1; setCurrentItemInternal(nextPage, true, true, initialVelocity); mActivePointerId = INVALID_POINTER; endDrag(); needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease(); } break; case MotionEvent.ACTION_CANCEL: if (mIsBeingDragged) { setCurrentItemInternal(mCurItem, true, true); mActivePointerId = INVALID_POINTER; endDrag(); needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease(); } break; case MotionEventCompat.ACTION_POINTER_DOWN: { final int index = MotionEventCompat.getActionIndex(ev); final float x = MotionEventCompat.getX(ev, index); mLastMotionX = x; mActivePointerId = MotionEventCompat.getPointerId(ev, index); break; } case MotionEventCompat.ACTION_POINTER_UP: onSecondaryPointerUp(ev); mLastMotionX = MotionEventCompat.getX(ev, MotionEventCompat.findPointerIndex(ev, mActivePointerId)); break; } if (needsInvalidate) { invalidate(); } return true; } @Override public void draw(Canvas canvas) { super.draw(canvas); boolean needsInvalidate = false; final int overScrollMode = ViewCompat.getOverScrollMode(this); if (overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS || (overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS && mAdapter != null && mAdapter.getCount() > 1)) { if (!mLeftEdge.isFinished()) { final int restoreCount = canvas.save(); final int height = getHeight() - getPaddingTop() - getPaddingBottom(); canvas.rotate(270); canvas.translate(-height + getPaddingTop(), 0); mLeftEdge.setSize(height, getWidth()); needsInvalidate |= mLeftEdge.draw(canvas); canvas.restoreToCount(restoreCount); } if (!mRightEdge.isFinished()) { final int restoreCount = canvas.save(); final int width = getWidth(); final int height = getHeight() - getPaddingTop() - getPaddingBottom(); final int itemCount = mAdapter != null ? mAdapter.getCount() : 1; canvas.rotate(90); canvas.translate(-getPaddingTop(), -itemCount * (width + mPageMargin) + mPageMargin); mRightEdge.setSize(height, width); needsInvalidate |= mRightEdge.draw(canvas); canvas.restoreToCount(restoreCount); } } else { mLeftEdge.finish(); mRightEdge.finish(); } if (needsInvalidate) { // Keep animating invalidate(); } } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); // Draw the margin drawable if needed. if (mPageMargin > 0 && mMarginDrawable != null) { final int scrollX = getScrollX(); final int width = getWidth(); final int offset = scrollX % (width + mPageMargin); if (offset != 0) { // Pages fit completely when settled; we only need to draw when in between final int left = scrollX - offset + width; mMarginDrawable.setBounds(left, 0, left + mPageMargin, getHeight()); mMarginDrawable.draw(canvas); } } } /** * Start a fake drag of the pager. * * <p>A fake drag can be useful if you want to synchronize the motion of the ViewPager * with the touch scrolling of another view, while still letting the ViewPager * control the snapping motion and fling behavior. (e.g. parallax-scrolling tabs.) * Call {@link #fakeDragBy(float)} to simulate the actual drag motion. Call * {@link #endFakeDrag()} to complete the fake drag and fling as necessary. * * <p>During a fake drag the ViewPager will ignore all touch events. If a real drag * is already in progress, this method will return false. * * @return true if the fake drag began successfully, false if it could not be started. * * @see #fakeDragBy(float) * @see #endFakeDrag() */ public boolean beginFakeDrag() { if (mIsBeingDragged) { return false; } mFakeDragging = true; setScrollState(SCROLL_STATE_DRAGGING); mInitialMotionX = mLastMotionX = 0; if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } else { mVelocityTracker.clear(); } final long time = SystemClock.uptimeMillis(); final MotionEvent ev = MotionEvent.obtain(time, time, MotionEvent.ACTION_DOWN, 0, 0, 0); mVelocityTracker.addMovement(ev); ev.recycle(); mFakeDragBeginTime = time; return true; } /** * End a fake drag of the pager. * * @see #beginFakeDrag() * @see #fakeDragBy(float) */ public void endFakeDrag() { if (!mFakeDragging) { throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first."); } final VelocityTracker velocityTracker = mVelocityTracker; velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity); int initialVelocity = (int)VelocityTrackerCompat.getYVelocity( velocityTracker, mActivePointerId); mPopulatePending = true; if ((Math.abs(initialVelocity) > mMinimumVelocity) || Math.abs(mInitialMotionX-mLastMotionX) >= (getWidth()/3)) { if (mLastMotionX > mInitialMotionX) { setCurrentItemInternal(mCurItem-1, true, true); } else { setCurrentItemInternal(mCurItem+1, true, true); } } else { setCurrentItemInternal(mCurItem, true, true); } endDrag(); mFakeDragging = false; } /** * Fake drag by an offset in pixels. You must have called {@link #beginFakeDrag()} first. * * @param xOffset Offset in pixels to drag by. * @see #beginFakeDrag() * @see #endFakeDrag() */ public void fakeDragBy(float xOffset) { if (!mFakeDragging) { throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first."); } mLastMotionX += xOffset; float scrollX = getScrollX() - xOffset; final int width = getWidth(); final int widthWithMargin = width + mPageMargin; final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin); final float rightBound = Math.min(mCurItem + 1, mAdapter.getCount() - 1) * widthWithMargin; if (scrollX < leftBound) { scrollX = leftBound; } else if (scrollX > rightBound) { scrollX = rightBound; } // Don't lose the rounded component mLastMotionX += scrollX - (int) scrollX; scrollTo((int) scrollX, getScrollY()); if (mOnPageChangeListener != null) { final int position = (int) scrollX / widthWithMargin; final int positionOffsetPixels = (int) scrollX % widthWithMargin; final float positionOffset = (float) positionOffsetPixels / widthWithMargin; mOnPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels); } // Synthesize an event for the VelocityTracker. final long time = SystemClock.uptimeMillis(); final MotionEvent ev = MotionEvent.obtain(mFakeDragBeginTime, time, MotionEvent.ACTION_MOVE, mLastMotionX, 0, 0); mVelocityTracker.addMovement(ev); ev.recycle(); } /** * Returns true if a fake drag is in progress. * * @return true if currently in a fake drag, false otherwise. * * @see #beginFakeDrag() * @see #fakeDragBy(float) * @see #endFakeDrag() */ public boolean isFakeDragging() { return mFakeDragging; } private void onSecondaryPointerUp(MotionEvent ev) { final int pointerIndex = MotionEventCompat.getActionIndex(ev); final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex); if (pointerId == mActivePointerId) { // This was our active pointer going up. Choose a new // active pointer and adjust accordingly. final int newPointerIndex = pointerIndex == 0 ? 1 : 0; mLastMotionX = MotionEventCompat.getX(ev, newPointerIndex); mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex); if (mVelocityTracker != null) { mVelocityTracker.clear(); } } } private void endDrag() { mIsBeingDragged = false; mIsUnableToDrag = false; if (mVelocityTracker != null) { mVelocityTracker.recycle(); mVelocityTracker = null; } } private void setScrollingCacheEnabled(boolean enabled) { if (mScrollingCacheEnabled != enabled) { mScrollingCacheEnabled = enabled; if (USE_CACHE) { final int size = getChildCount(); for (int i = 0; i < size; ++i) { final View child = getChildAt(i); if (child.getVisibility() != GONE) { child.setDrawingCacheEnabled(enabled); } } } } } /** * Tests scrollability within child views of v given a delta of dx. * * @param v View to test for horizontal scrollability * @param checkV Whether the view v passed should itself be checked for scrollability (true), * or just its children (false). * @param dx Delta scrolled in pixels * @param x X coordinate of the active touch point * @param y Y coordinate of the active touch point * @return true if child views of v can be scrolled by delta of dx. */ protected boolean canScroll(View v, boolean checkV, int dx, int x, int y) { if (v instanceof ViewGroup) { final ViewGroup group = (ViewGroup) v; final int scrollX = v.getScrollX(); final int scrollY = v.getScrollY(); final int count = group.getChildCount(); // Count backwards - let topmost views consume scroll distance first. for (int i = count - 1; i >= 0; i--) { // TODO: Add versioned support here for transformed views. // This will not work for transformed views in Honeycomb+ final View child = group.getChildAt(i); if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight() && y + scrollY >= child.getTop() && y + scrollY < child.getBottom() && canScroll(child, true, dx, x + scrollX - child.getLeft(), y + scrollY - child.getTop())) { return true; } } } return checkV && ViewCompat.canScrollHorizontally(v, -dx); } @Override public boolean dispatchKeyEvent(KeyEvent event) { // Let the focused view and/or our descendants get the key first return super.dispatchKeyEvent(event) || executeKeyEvent(event); } /** * You can call this function yourself to have the scroll view perform * scrolling from a key event, just as if the event had been dispatched to * it by the view hierarchy. * * @param event The key event to execute. * @return Return true if the event was handled, else false. */ public boolean executeKeyEvent(KeyEvent event) { boolean handled = false; if (event.getAction() == KeyEvent.ACTION_DOWN) { switch (event.getKeyCode()) { case KeyEvent.KEYCODE_DPAD_LEFT: handled = arrowScroll(FOCUS_LEFT); break; case KeyEvent.KEYCODE_DPAD_RIGHT: handled = arrowScroll(FOCUS_RIGHT); break; case KeyEvent.KEYCODE_TAB: if (KeyEventCompat.hasNoModifiers(event)) { handled = arrowScroll(FOCUS_FORWARD); } else if (KeyEventCompat.hasModifiers(event, KeyEvent.META_SHIFT_ON)) { handled = arrowScroll(FOCUS_BACKWARD); } break; } } return handled; } public boolean arrowScroll(int direction) { View currentFocused = findFocus(); if (currentFocused == this) currentFocused = null; boolean handled = false; View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction); if (nextFocused != null && nextFocused != currentFocused) { if (direction == View.FOCUS_LEFT) { // If there is nothing to the left, or this is causing us to // jump to the right, then what we really want to do is page left. if (currentFocused != null && nextFocused.getLeft() >= currentFocused.getLeft()) { handled = pageLeft(); } else { handled = nextFocused.requestFocus(); } } else if (direction == View.FOCUS_RIGHT) { // If there is nothing to the right, or this is causing us to // jump to the left, then what we really want to do is page right. if (currentFocused != null && nextFocused.getLeft() <= currentFocused.getLeft()) { handled = pageRight(); } else { handled = nextFocused.requestFocus(); } } } else if (direction == FOCUS_LEFT || direction == FOCUS_BACKWARD) { // Trying to move left and nothing there; try to page. handled = pageLeft(); } else if (direction == FOCUS_RIGHT || direction == FOCUS_FORWARD) { // Trying to move right and nothing there; try to page. handled = pageRight(); } if (handled) { playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction)); } return handled; } boolean pageLeft() { if (mCurItem > 0) { setCurrentItem(mCurItem-1, true); return true; } return false; } boolean pageRight() { if (mAdapter != null && mCurItem < (mAdapter.getCount()-1)) { setCurrentItem(mCurItem+1, true); return true; } return false; } /** * We only want the current page that is being shown to be focusable. */ @Override public void addFocusables(ArrayList<View> views, int direction, int focusableMode) { final int focusableCount = views.size(); final int descendantFocusability = getDescendantFocusability(); if (descendantFocusability != FOCUS_BLOCK_DESCENDANTS) { for (int i = 0; i < getChildCount(); i++) { final View child = getChildAt(i); if (child.getVisibility() == VISIBLE) { ItemInfo ii = infoForChild(child); if (ii != null && ii.position == mCurItem) { child.addFocusables(views, direction, focusableMode); } } } } // we add ourselves (if focusable) in all cases except for when we are // FOCUS_AFTER_DESCENDANTS and there are some descendants focusable. this is // to avoid the focus search finding layouts when a more precise search // among the focusable children would be more interesting. if ( descendantFocusability != FOCUS_AFTER_DESCENDANTS || // No focusable descendants (focusableCount == views.size())) { // Note that we can't call the superclass here, because it will // add all views in. So we need to do the same thing View does. if (!isFocusable()) { return; } if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE && isInTouchMode() && !isFocusableInTouchMode()) { return; } if (views != null) { views.add(this); } } } /** * We only want the current page that is being shown to be touchable. */ @Override public void addTouchables(ArrayList<View> views) { // Note that we don't call super.addTouchables(), which means that // we don't call View.addTouchables(). This is okay because a ViewPager // is itself not touchable. for (int i = 0; i < getChildCount(); i++) { final View child = getChildAt(i); if (child.getVisibility() == VISIBLE) { ItemInfo ii = infoForChild(child); if (ii != null && ii.position == mCurItem) { child.addTouchables(views); } } } } /** * We only want the current page that is being shown to be focusable. */ @Override protected boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect) { int index; int increment; int end; int count = getChildCount(); if ((direction & FOCUS_FORWARD) != 0) { index = 0; increment = 1; end = count; } else { index = count - 1; increment = -1; end = -1; } for (int i = index; i != end; i += increment) { View child = getChildAt(i); if (child.getVisibility() == VISIBLE) { ItemInfo ii = infoForChild(child); if (ii != null && ii.position == mCurItem) { if (child.requestFocus(direction, previouslyFocusedRect)) { return true; } } } } return false; } @Override public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event) { // ViewPagers should only report accessibility info for the current page, // otherwise things get very confusing. // TODO: Should this note something about the paging container? final int childCount = getChildCount(); for (int i = 0; i < childCount; i++) { final View child = getChildAt(i); if (child.getVisibility() == VISIBLE) { final ItemInfo ii = infoForChild(child); if (ii != null && ii.position == mCurItem && child.dispatchPopulateAccessibilityEvent(event)) { return true; } } } return false; } private class PagerObserver ex