带阻尼效果的scrollview，仿QQ空间

修复上个版本已知的BUG，效果更好

package com.okdai;

import android.content.Context;
import android.graphics.Rect;
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 {
private static final int LEN = 0xc8;
private static final int DURATION = 500;
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;
}


@Override
protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect) {


return 0;
}


private int[] li = new int[2];
private int[] li2 = new int[2];
private float lastLy;
private boolean startIsTop = true;


@Override
public boolean dispatchTouchEvent(MotionEvent event) {
super.dispatchTouchEvent(event);
int action = event.getAction();
if (!mScroller.isFinished()) {
return super.onTouchEvent(event);
}
currentX = event.getX();
currentY = event.getY();
imageView.getLocationInWindow(li);
getLocationOnScreen(li2);
imageView.getTop();
switch (action) {
case MotionEvent.ACTION_DOWN:
if (li[1] != li2[1]) {// 判断开始触摸时，imageview和窗口顶部对齐没
startIsTop = false;
}
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 (!startIsTop && li[1] == li2[1]) {
startY = currentY;
startIsTop = true;
} 
if (imageView.isShown() && imageView.getTop() >= 0) {
if (tool != null) {
int t = tool.getScrollY(currentY - startY);
if (!scrollerType && currentY < lastLy && imageView.getHeight() > imageViewH) {
scrollTo(0, 0);
imageView.getLocationInWindow(li);
getLocationOnScreen(li2);
android.view.ViewGroup.LayoutParams params = imageView.getLayoutParams();
params.height = t;
imageView.setLayoutParams(params);
if (imageView.getHeight() == imageViewH && li[1] == li2[1]) {
scrollerType = true;
}
if (startIsTop && li[1] != li2[1]) {
startIsTop = false;
}
}
if (t >= top && t <= imageView.getBottom() + LEN && li[1] == li2[1] && currentY > lastLy) {
android.view.ViewGroup.LayoutParams params = imageView.getLayoutParams();
params.height = t;
imageView.setLayoutParams(params);
}
}
scrollerType = false;
}


lastLy = currentY;
break;
case MotionEvent.ACTION_UP:
if (li[1] == li2[1]) {
scrollerType = true;
mScroller.startScroll(imageView.getLeft(), imageView.getBottom(), 0 - imageView.getLeft(),
imageViewH - imageView.getBottom(), DURATION);
invalidate();
}
startIsTop = true;
break;
}


return true;
}


@Override
public void computeScroll() {
super.computeScroll();
if (mScroller.computeScrollOffset()) {
int x = mScroller.getCurrX();
int y = mScroller.getCurrY();
imageView.layout(0, 0, x + imageView.getWidth(), y);
invalidate();
if (!mScroller.isFinished() && scrollerType && y > MAX_DY) {
android.view.ViewGroup.LayoutParams params = imageView.getLayoutParams();
params.height = y;
imageView.setLayoutParams(params);
}
}
}


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);
return yy;
}
}
}