安卓仿朋友圈下拉背景图片拉伸，松手反弹效果

先讲一下思路，主要就是通过监听手指滑动事件，根据滑动距离对目标view的width、height进行变化以及margin的设置，回弹时则是根据监听属性动画进行设置，话不多说上代码。

public class HeadZoomScrollView extends ScrollView {

    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);
    }

    //用于记录下拉位置
    private float y = 0f;
    //zoomView原本的宽高
    private int zoomViewWidth = 0;
    private int zoomViewHeight = 0;

    //是否正在放大
    private boolean mScaling = false;

    //放大的view，默认为第一个子view
    private View zoomView;
    public void setZoomView(View zoomView) {
        this.zoomView = zoomView;
    }

    //滑动放大系数，系数越大，滑动时放大程度越大
    private float mScaleRatio = 0.4f;
    public void setmScaleRatio(float mScaleRatio) {
        this.mScaleRatio = mScaleRatio;
    }

    //最大的放大倍数
    private float mScaleTimes = 2f;
    public void setmScaleTimes(int mScaleTimes) {
        this.mScaleTimes = mScaleTimes;
    }

    //回弹时间系数，系数越小，回弹越快
    private float mReplyRatio = 0.5f;
    public void setmReplyRatio(float mReplyRatio) {
        this.mReplyRatio = mReplyRatio;
    }

    //滚动触发子view横向放大的方法
    private float moveDistance=300.0f;
    public void setMoveDistance(float moveDistance){
        this.moveDistance=moveDistance;
    }

	//是否横向拉伸，默认为true
	private boolean isTransverse=true;
	public void setTransverse(boolean isTransverse){
		this.isTransverse=isTransverse;
	}

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        //不可过度滚动，否则上移后下拉会出现部分空白的情况
        setOverScrollMode(OVER_SCROLL_NEVER);
        //获得默认第一个view
        if (getChildAt(0) != null && getChildAt(0) instanceof ViewGroup && zoomView == null) {
            ViewGroup vg = (ViewGroup) getChildAt(0);
            if (vg.getChildCount() > 0) {
                zoomView = vg.getChildAt(0);
            }
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
       if (zoomViewWidth <= 0 || zoomViewHeight <= 0) {
            zoomViewWidth = zoomView.getMeasuredWidth();
            zoomViewHeight = zoomView.getMeasuredHeight();
        }
        switch (ev.getAction()) {
            case MotionEvent.ACTION_UP:
                //手指离开后恢复图片
                mScaling = false;
                replyImage();
                break;
            case MotionEvent.ACTION_MOVE:
                if (!mScaling) {
                    if (getScrollY() == 0) {
                        y = 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() - y) * mScaleRatio); // 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
                mScaling = true;
                setZoom(distance);
                return true; // 返回true表示已经完成触摸事件，不再处理
        }
        return true;
    }

  //拉伸效果
  public void setZoom(float zoom) {
        if (zoomViewWidth <= 0 || zoomViewHeight <= 0) {
            return;
        }
        ViewGroup.LayoutParams lp = zoomView.getLayoutParams();
        if(isTransverse){
          if(zoom<=moveDistance){
          	lp.width = (int) (zoomViewWidth);
          }else{
          	lp.width = (int) (zoomViewWidth+zoom);
          }
        }else{
          lp.width = (int) (zoomViewWidth);
        }
        lp.height = (int) (zoomViewHeight * ((zoomViewWidth + zoom) / zoomViewWidth));
        ((MarginLayoutParams) lp).setMargins(-(lp.width - zoomViewWidth) / 2, 0, 0, 0);
        zoomView.setLayoutParams(lp);
    }

	 //回弹动画
    private void replyImage() {
        float distance = zoomView.getMeasuredWidth() - zoomViewWidth;
        ValueAnimator valueAnimator = ValueAnimator.ofFloat(distance, 0f).setDuration((long) (distance * mReplyRatio));
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                setZoom((Float) animation.getAnimatedValue());
            }
        });
        valueAnimator.start();
    }

  }  

下面是在activity布局中的使用，该控件子布局只能为一个布局控件（如LinearLayout、RelativeLayout），其实就是跟ScrollView的使用基本一致，这里就不做过多的叙述了，大家都懂的。

<com.kesaba.test.HeadZoomScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/scrollView"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
 
        <ImageView
            android:id="@+id/iv_show"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:layout_weight="1"
            android:src="@drawable/a1"/>
		
		......
		
    </LinearLayout>
 
</com.kesaba.test.HeadZoomScrollView>

本文地址：https://blog.csdn.net/weixin_41078051/article/details/108720498