自定义ScrollView下拉头部变大，弹性动画缩回原型

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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();    }}
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