Android怎么实现背景图滑动变大松开回弹效果

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原图

放大后

1、自定义view继承ScrollView实现效果

public class HeadZoomScrollView extends ScrollView {    private View mZoomView;    private int mZoomViewWidth;    private int mZoomViewHeight;    private float firstPosition;//记录第一次按下的位置    private boolean isScrolling;//是否正在缩放    private float mScrollRate = 0.3f;//缩放系数，缩放系数越大，变化的越大    private float mReplyRate = 0.5f;//回调系数，越大，回调越慢    public HeadZoomScrollView(Context context) {        super(context);    }    public HeadZoomScrollView(Context context, AttributeSet attrs) {        super(context, attrs);    }    public HeadZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);    }    public void setmZoomView(View mZoomView) {        this.mZoomView = mZoomView;    }    public void setmScrollRate(float mScrollRate) {        this.mScrollRate = mScrollRate;    }    public void setmReplyRate(float mReplyRate) {        this.mReplyRate = mReplyRate;    }    @Override    protected void onFinishInflate() {        super.onFinishInflate();        init();    }    private void init() {        setOverScrollMode(OVER_SCROLL_NEVER);        if (getChildAt(0) != null) {            ViewGroup vg = (ViewGroup) getChildAt(0);            if (vg.getChildAt(0) != null) {                mZoomView = vg.getChildAt(0);            }        }    }    @Override    public boolean onTouchEvent(MotionEvent ev) {        if (mZoomViewWidth <= 0 || mZoomViewHeight <= 0) {            mZoomViewWidth = mZoomView.getMeasuredWidth();            mZoomViewHeight = mZoomView.getMeasuredHeight();        }        switch (ev.getAction()) {            case MotionEvent.ACTION_UP:                //手指离开后恢复图片                isScrolling = false;                replyImage();                break;            case MotionEvent.ACTION_MOVE:                if (!isScrolling) {                    if (getScrollY() == 0) {                        firstPosition = ev.getY();// 滚动到顶部时记录位置，否则正常返回                    } else {                        break;                    }                }                int distance = (int) ((ev.getY() - firstPosition) * mScrollRate); // 滚动距离乘以一个系数                if (distance < 0) { // 当前位置比记录位置要小，正常返回                    break;                }                // 处理放大                isScrolling = true;                setZoom(distance);                return true; // 返回true表示已经完成触摸事件，不再处理        }        return true;    }    //回弹动画    private void replyImage() {        float distance = mZoomView.getMeasuredWidth() - mZoomViewWidth;        ValueAnimator valueAnimator = ValueAnimator.ofFloat(distance, 0f).setDuration((long) (distance * mReplyRate));        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator animation) {                setZoom((Float) animation.getAnimatedValue());            }        });        valueAnimator.start();    }    public void setZoom(float zoom) {        if (mZoomViewWidth <= 0 || mZoomViewHeight <= 0) {            return;        }        ViewGroup.LayoutParams lp = mZoomView.getLayoutParams();        lp.width = (int) (mZoomViewWidth + zoom);        lp.height = (int) (mZoomViewHeight * ((mZoomViewWidth + zoom) / mZoomViewWidth));        ((MarginLayoutParams) lp).setMargins(-(lp.width - mZoomViewWidth) / 2, 0, -(lp.width - mZoomViewWidth) / 2, 0);        mZoomView.setLayoutParams(lp);    }}

2、直接布局中使用这个view就可以，要注意的是在布局中需要在自定义view下写一个子控件才能使用

<你的包名.HeadZoomScrollView xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/drop_down_menu"    android:layout_width="match_parent"    android:layout_height="match_parent"   >                

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