阻尼效果即是图片向下拉动时会放大，松开会回弹
1.自定义一个DampView类，继承ScrollView
2.布局最外层必须是DampView,且DampView和要拉动的图片之间只能有一层layout（切记）
3.Activity中调用
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ImageView;
import android.widget.ScrollView;
import android.widget.Scroller; /**
* 阻尼效果的scrollview
*/
public class DampView extends ScrollView {
/** 该属性具体参数 怎么控制 未解！！！！*/
private static final int LEN = 0xc8;
/** 回弹时所用的时间 */
private static final int DURATION = 200;
// private static final int MAX_DY = 200;
/** 最大Y坐标 其值一般设定为Scroller对应控件的高度 */
private static final int MAX_DY = 200;
private Scroller mScroller;
TouchTool tool;
int left, top;
float startX, startY, currentX, currentY;
int imageViewH;
int rootW, rootH;
ImageView imageView;
boolean scrollerType; public DampView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle); } public DampView(Context context, AttributeSet attrs) {
super(context, attrs);
mScroller = new Scroller(context);
} public DampView(Context context) {
super(context); } public void setImageView(ImageView imageView) {
this.imageView = imageView;
} float curY;
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
if (!mScroller.isFinished()) {
return super.onTouchEvent(event);
}
currentX = event.getX();
currentY = event.getY();
imageView.getTop();
switch (action) {
case MotionEvent.ACTION_DOWN:// 变量赋初始值
left = imageView.getLeft();
top = imageView.getBottom();
rootW = getWidth();
rootH = getHeight(); imageViewH = imageView.getHeight();
startX = currentX;
startY = currentY;
tool = new TouchTool(imageView.getLeft(), imageView.getBottom(),
imageView.getLeft(), imageView.getBottom() + LEN);
break;
case MotionEvent.ACTION_MOVE:
if (imageView.isShown() && imageView.getTop() >= 0) {
if (tool != null) {
int t = tool.getScrollY(currentY - startY);
if (t >= top && t <= imageView.getBottom() + LEN) {
android.view.ViewGroup.LayoutParams params = imageView
.getLayoutParams();
params.height = t;// 改变高度
imageView.setLayoutParams(params);
} }
scrollerType = false;
}
break;
case MotionEvent.ACTION_UP:
scrollerType = true; // 松手后 回弹
// 开始一个动画控制，由(startX , startY)在duration时间内前进(dx,dy)个单位
// ，即到达坐标为(startX+dx , startY+dy)处
mScroller.startScroll(imageView.getLeft(), imageView.getBottom(),
0 - imageView.getLeft(),
imageViewH - imageView.getBottom(), DURATION);
invalidate();
break;
} return super.dispatchTouchEvent(event);
} // //该mScroller针对于imageView的变化
// 被父视图调用，用于必要时候对其子视图的值（mScrollX和mScrollY）
// 进行更新。典型的情况如：父视图中某个子视图使用一个Scroller对象来实现滚动操作，会使得此方法被调用。
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
int x = mScroller.getCurrX();
int y = mScroller.getCurrY();// ImageView的当前Y坐标
imageView.layout(0, 0, x + imageView.getWidth(), y);//使imageView本身做相应变化
invalidate(); // 滑动还未完成时，手指抬起时，当前y坐标大于其实imageView的高度时
//设定imageView的布局参数 作用：使除imageView之外的控件做相应变化
if (!mScroller.isFinished() && scrollerType && y > MAX_DY) {
android.view.ViewGroup.LayoutParams params = imageView
.getLayoutParams();
params.height = y;
imageView.setLayoutParams(params);
}
// invalidate();
}
} public class TouchTool { private int startX, startY; public TouchTool(int startX, int startY, int endX, int endY) {
super();
this.startX = startX;
this.startY = startY;
} public int getScrollX(float dx) {
int xx = (int) (startX + dx / 2.5F);
return xx;
} public int getScrollY(float dy) {
int yy = (int) (startY + dy / 2.5F);//手势滑动距离/2.5 才是屏幕滑动的距离 此内部类主要做此用
return yy;
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<de.hdodenhof.damp.DampView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/dampview"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" > <!--此处必须设置imageview的scaleType为centerCrop,当然在代码中设置也可以-->
<ImageView
android:id="@+id/img"
android:layout_width="match_parent"
android:layout_height="200dp"
android:scaleType="centerCrop"
android:src="@drawable/bg_geren" /> </LinearLayout> </de.hdodenhof.damp.DampView>
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView; public class MainActivity extends AppCompatActivity { private ImageView img; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setupView();
} public void setupView() {
img = (ImageView) findViewById(R.id.img);
DampView view = (DampView) findViewById(R.id.dampview);
view.setImageView(img);
}
}