我试图修改google io应用程序中的slidingtablayout，使活动选项卡始终锁定在中间，就像最新的google play报摊和foursquare版本一样。我该怎么实施呢？
最佳答案
我修改了slidingtablayout，以便包含选项卡的水平滚动视图根据viewpager的滚动偏移量调整其填充。我花了3天时间才得到一个可以接受的结果，我希望它也能帮助你！如果您有任何问题和/或改进，请评论！
滑动tablayout.java
/*
* Copyright 2014 Google Inc. All rights reserved.
*
* 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.animation.LayoutTransition;
import android.content.Context;
import android.graphics.Rect;
import android.graphics.Typeface;
import android.os.Build;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.Log;
import android.util.SparseArray;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;
import android.widget.TextView;
/**
* To be used with ViewPager to provide a tab indicator component which give constant feedback as to
* the user's scroll progress.
* <p/>
* To use the component, simply add it to your view hierarchy. Then in your
* {@link android.app.Activity} or {@link android.support.v4.app.Fragment} call
* {@link #setViewPager(ViewPager)} providing it the ViewPager this layout is being used for.
* <p/>
* The colors can be customized in two ways. The first and simplest is to provide an array of colors
* via {@link #setSelectedIndicatorColors(int...)}. The
* alternative is via the {@link TabColorizer} interface which provides you complete control over
* which color is used for any individual position.
* <p/>
* The views used as tabs can be customized by calling {@link #setCustomTabView(int, int)},
* providing the layout ID of your custom layout.
*/
public class SlidingTabLayout extends HorizontalScrollView {
/**
* Allows complete control over the colors drawn in the tab layout. Set with
* {@link #setCustomTabColorizer(TabColorizer)}.
*/
public interface TabColorizer {
/**
* @return return the color of the indicator used when {@code position} is selected.
*/
int getIndicatorColor(int position);
}
private static final int TAB_VIEW_PADDING_DIPS = 16;
private static final int TAB_VIEW_TEXT_SIZE_SP = 12;
private int mTabViewLayoutId;
private int mTabViewTextViewId;
private boolean mDistributeEvenly;
private ViewPager mViewPager;
private SparseArray<String> mContentDescriptions = new SparseArray<String>();
private ViewPager.OnPageChangeListener mViewPagerPageChangeListener;
private final SlidingTabStrip mTabStrip;
public SlidingTabLayout(Context context) {
this(context, null);
}
public SlidingTabLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SlidingTabLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// Disable the Scroll Bar
setHorizontalScrollBarEnabled(false);
// Make sure that the Tab Strips fills this View
setFillViewport(true);
mTabStrip = new SlidingTabStrip(context);
//mTabStrip.setVisibility(View.INVISIBLE);
addView(mTabStrip, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
// Set spacer tab widths
View firstTab = mTabStrip.getChildAt(0);
int firstTabPadding = (getWidth() - mTabStrip.getChildAt(1).getMeasuredWidth()) / 2;
firstTab.setPadding(firstTabPadding, firstTab.getPaddingTop(), firstTab.getPaddingRight(), firstTab.getPaddingBottom());
View lastTab = mTabStrip.getChildAt(mTabStrip.getChildCount() - 1);
int lastTabPadding = (getWidth() - mTabStrip.getChildAt(mTabStrip.getChildCount() - 2).getMeasuredWidth()) / 4;
lastTab.setPadding(lastTabPadding, 0, lastTabPadding, 0);
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1)
getViewTreeObserver().removeOnGlobalLayoutListener(this);
else
getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
});
}
/**
* Set the custom {@link TabColorizer} to be used.
* <p/>
* If you only require simple customisation then you can use
* {@link #setSelectedIndicatorColors(int...)} to achieve
* similar effects.
*/
public void setCustomTabColorizer(TabColorizer tabColorizer) {
mTabStrip.setCustomTabColorizer(tabColorizer);
}
public void setDistributeEvenly(boolean distributeEvenly) {
mDistributeEvenly = distributeEvenly;
}
/**
* Sets the colors to be used for indicating the selected tab. These colors are treated as a
* circular array. Providing one color will mean that all tabs are indicated with the same color.
*/
public void setSelectedIndicatorColors(int... colors) {
mTabStrip.setSelectedIndicatorColors(colors);
}
/**
* Set the {@link ViewPager.OnPageChangeListener}. When using {@link SlidingTabLayout} you are
* required to set any {@link ViewPager.OnPageChangeListener} through this method. This is so
* that the layout can update it's scroll position correctly.
*
* @see ViewPager#setOnPageChangeListener(ViewPager.OnPageChangeListener)
*/
public void setOnPageChangeListener(ViewPager.OnPageChangeListener listener) {
mViewPagerPageChangeListener = listener;
}
/**
* Set the custom layout to be inflated for the tab views.
*
* @param layoutResId Layout id to be inflated
* @param textViewId id of the {@link TextView} in the inflated view
*/
public void setCustomTabView(int layoutResId, int textViewId) {
mTabViewLayoutId = layoutResId;
mTabViewTextViewId = textViewId;
}
/**
* Sets the associated view pager. Note that the assumption here is that the pager content
* (number of tabs and tab titles) does not change after this call has been made.
*/
public void setViewPager(ViewPager viewPager) {
mTabStrip.removeAllViews();
mViewPager = viewPager;
if (viewPager != null) {
viewPager.setOnPageChangeListener(new InternalViewPagerListener());
populateTabStrip();
}
}
/**
* Create a default view to be used for tabs. This is called if a custom tab view is not set via
* {@link #setCustomTabView(int, int)}.
*/
protected TextView createDefaultTabView(Context context) {
TextView textView = new TextView(context);
textView.setGravity(Gravity.CENTER);
textView.setTextSize(TypedValue.COMPLEX_UNIT_SP, TAB_VIEW_TEXT_SIZE_SP);
textView.setTypeface(Typeface.DEFAULT_BOLD);
textView.setLayoutParams(new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
TypedValue outValue = new TypedValue();
getContext().getTheme().resolveAttribute(android.R.attr.selectableItemBackground,
outValue, true);
textView.setBackgroundResource(outValue.resourceId);
textView.setAllCaps(true);
int padding = (int) (TAB_VIEW_PADDING_DIPS * getResources().getDisplayMetrics().density);
textView.setPadding(padding, padding, padding, padding);
return textView;
}
private void populateTabStrip() {
final PagerAdapter adapter = mViewPager.getAdapter();
final View.OnClickListener tabClickListener = new TabClickListener();
for (int i = 0; i < adapter.getCount(); i++) {
View tabView = null;
TextView tabTitleView = null;
if (mTabViewLayoutId != 0) {
// If there is a custom tab view layout id set, try and inflate it
tabView = LayoutInflater.from(getContext()).inflate(mTabViewLayoutId, mTabStrip,
false);
tabTitleView = (TextView) tabView.findViewById(mTabViewTextViewId);
}
if (tabView == null) {
tabView = createDefaultTabView(getContext());
}
if (tabTitleView == null && TextView.class.isInstance(tabView)) {
tabTitleView = (TextView) tabView;
}
if (mDistributeEvenly) {
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) tabView.getLayoutParams();
lp.width = 0;
lp.weight = 1;
}
tabTitleView.setText(adapter.getPageTitle(i));
tabView.setOnClickListener(tabClickListener);
String desc = mContentDescriptions.get(i, null);
if (desc != null) {
tabView.setContentDescription(desc);
}
mTabStrip.addView(tabView);
if (i == mViewPager.getCurrentItem()) {
tabView.setSelected(true);
}
}
// First spacer tab
TextView firstTab = new TextView(getContext());
mTabStrip.addView(firstTab, 0);
// Last spacer tab
TextView lastTab = new TextView(getContext());
mTabStrip.addView(lastTab);
}
public void setContentDescription(int i, String desc) {
mContentDescriptions.put(i, desc);
}
private void scrollToTab(int tabIndex, int positionOffset) {
final int tabStripChildCount = mTabStrip.getChildCount();
if (tabStripChildCount == 0 || tabIndex < 0 || tabIndex >= tabStripChildCount) {
return;
}
if (positionOffset == -1) {// Not manual scroll. Do not animate. Just cut to tab and center.
if (tabIndex == 1)
positionOffset = 0;
else
positionOffset = mTabStrip.getChildAt(tabIndex).getWidth() / 2 + mTabStrip.getChildAt(tabIndex + 1).getWidth() / 2;
}
if (tabIndex == 1) // if tab number one, no need to calculate previously scrolled X
scrollTo(positionOffset, 0);
else { // If tab number is greater than 1, we need to calculate previously scrolled X
int previouslyScrolledX = 0;
// Simulate previously scrolled X by summing half of each of the previous tabs' width.
// Use 2 tabs per loop for correct simulation.
for (int i = 1; i < tabIndex; i++) {
previouslyScrolledX += mTabStrip.getChildAt(i).getWidth() / 2;
previouslyScrolledX += mTabStrip.getChildAt(i + 1).getWidth() / 2;
}
scrollTo(previouslyScrolledX + positionOffset, 0);
}
}
private class InternalViewPagerListener implements ViewPager.OnPageChangeListener {
private int mScrollState;
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
int tabStripChildCount = mTabStrip.getChildCount();
if ((tabStripChildCount == 0) || (position < 0) || (position >= tabStripChildCount)) {
return;
}
position++; // Offset position by 1 to make up for left blank tab
mTabStrip.onViewPagerPageChanged(position, positionOffset);
// Adding half of current tab's width & half of next tab's width and scrolling by that width will center next tab
int offsetToCenterNextTab = (mTabStrip.getChildAt(position).getWidth() / 2) + (mTabStrip.getChildAt(position + 1).getWidth() / 2);
scrollToTab(position, Math.round(offsetToCenterNextTab * positionOffset));
if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageScrolled(position, positionOffset,
positionOffsetPixels);
}
}
@Override
public void onPageScrollStateChanged(int state) {
mScrollState = state;
if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageScrollStateChanged(state);
}
}
@Override
public void onPageSelected(int position) {
if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
mTabStrip.onViewPagerPageChanged(position, 0f);
scrollToTab(position, -1);
}
for (int i = 0; i < mTabStrip.getChildCount(); i++) {
mTabStrip.getChildAt(i).setSelected(position + 1 == i);
}
if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageSelected(position);
}
}
}
private class TabClickListener implements View.OnClickListener {
@Override
public void onClick(View selectedView) {
View lastSelectedView = null;
int selectedViewIndex = 0;
for (int i = 1; i < mTabStrip.getChildCount() - 1; i++) {
View currentViewInLoop = mTabStrip.getChildAt(i);
if (currentViewInLoop.isSelected()) {
lastSelectedView = currentViewInLoop;
}
if (selectedView == currentViewInLoop) {
selectedViewIndex = i - 1;
}
if (lastSelectedView != null && selectedViewIndex != 0)
break;
}
Rect tabContainerRect = new Rect();
Rect lastSelectedTabRect = new Rect();
getDrawingRect(tabContainerRect);
lastSelectedView.getHitRect(lastSelectedTabRect);
if (Rect.intersects(tabContainerRect, lastSelectedTabRect))
mViewPager.setCurrentItem(selectedViewIndex);
else
mViewPager.setCurrentItem(selectedViewIndex, false);
}
}
}