自定义ScrollView下拉头部变大，弹性动画缩回原型

package demo.com.customviewdemo.customview;

import android.animation.Animator;
import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ScrollView;

/**
* Created by Alv_chi
*/
public class HeadZoomScrollView extends ScrollView {

private static final String TAG = "Test";
private View zoomHeadView;
private float mDownY;
private float mMoveY;
private float mDeltaY;
private boolean isZoomed;

private float zoomHeight;
private double zoomWindth;

private float ratio = 0.4f;
private int measuredWidth;
private int measuredHeight;

public HeadZoomScrollView(Context context) {
this(context, null);
}

public HeadZoomScrollView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}

public HeadZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
this(context, attrs, defStyleAttr, 0);
}

public HeadZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}

@Override
protected void onFinishInflate() {
super.onFinishInflate();

int childCount = getChildCount();
if (childCount > 0) {
View contentView = getChildAt(0);
if (contentView != null && contentView instanceof ViewGroup) {
ViewGroup vg = (ViewGroup) contentView;//ScroView中只能包含一个View；
int childNum = vg.getChildCount();
if (childNum > 0) {
zoomHeadView = vg.getChildAt(0);

}
}
}
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (measuredWidth <= 0 || measuredHeight <= 0) {
//            获取测量到的可变大得View原始参数
measuredWidth = zoomHeadView.getMeasuredWidth();
measuredHeight = zoomHeadView.getMeasuredHeight();

}
if (zoomHeadView == null || measuredWidth <= 0 || measuredHeight <= 0) {
return super.onTouchEvent(ev);
}

switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
mDownY = ev.getY();
break;
case MotionEvent.ACTION_MOVE:
mMoveY = ev.getY();
mDeltaY = mMoveY - mDownY;
if (mDeltaY > 10 && getScrollY() == 0) {
zoom(mDeltaY);
isZoomed = true;
return true;
}
break;
case MotionEvent.ACTION_UP:
if (isZoomed) {

replyView();
}
break;

}

return super.dispatchTouchEvent(ev);
}

private void zoom(float factor) {
//         通过改变参数改变view的大小：
ViewGroup.LayoutParams layoutParams = zoomHeadView.getLayoutParams();

zoomHeight = measuredHeight + factor * ratio;
zoomWindth = measuredWidth + factor * ratio;
layoutParams.height = (int) zoomHeight;
layoutParams.width = (int) zoomWindth;

zoomHeadView.setLayoutParams(layoutParams);

}

private void replyView() {
float delta = zoomHeadView.getMeasuredWidth() - measuredHeight;
// 设置动画，由delta * ratio变到0过程：
ValueAnimator anim = ObjectAnimator.ofFloat(delta * ratio, 0.0F).setDuration((long) (delta * ratio));

//        添加一个过程更新监听器：
anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
//逐帧拿到数据，逐帧缩小
zoom((Float) animation.getAnimatedValue());
}
});

anim.addListener(new Animator.AnimatorListener() {
@Override
public void onAnimationStart(Animator animation) {

}

@Override
public void onAnimationEnd(Animator animation) {
isZoomed = false;
}

@Override
public void onAnimationCancel(Animator animation) {

}

@Override
public void onAnimationRepeat(Animator animation) {

}
});
anim.start();

}
}