android下拉放大图片

private void setImage() {

        // 获取屏幕宽高
        metric = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metric);

        // 设置图片初始大小 这里我设为满屏的16:9,根据自己需要调整
        ViewGroup.LayoutParams lp = (ViewGroup.LayoutParams) ivHeader.getLayoutParams();
        lp.width = metric.widthPixels;
        lp.height = metric.widthPixels * 9 / 16;
        ivHeader.setLayoutParams(lp);

        // 设置触摸的监听事件
        mCeshi2.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                ViewGroup.LayoutParams lp = (ViewGroup.LayoutParams) ivHeader
                        .getLayoutParams();
                switch (event.getAction()) {
                    //手指抬起时触发
                    case MotionEvent.ACTION_UP:
                        // 手指离开后恢复图片
                        mScaling = false;
                        replyImage();
                        break;
                    //手指移动时触发
                    case MotionEvent.ACTION_MOVE:
                        if (!mScaling) {
                            if (mCeshi2.getScrollY() == 0) {
                                mFirstPosition = event.getY();// 滚动到顶部时记录位置，否则正常返回
                            } else {
                                break;
                            }
                        }
                        int distance = (int) ((event.getY() - mFirstPosition) * 0.6); // 滚动距离乘以一个系数
                        if (distance < 0) { // 如果当前位置比记录位置要小，正常返回
                            break;
                        }

                        // 处理放大的关键代码
                        mScaling = true;
                        lp.width = metric.widthPixels + distance;
                        lp.height = (metric.widthPixels + distance) * 9 / 16;
                        ivHeader.setLayoutParams(lp);
                        return true; // 返回true表示已经消费该事件
                }
                return false;
            }
        });

    }


    // 手指抬起图片回弹动画 (使用了属性动画)
    public void replyImage() {
        final ViewGroup.LayoutParams lp = (ViewGroup.LayoutParams) ivHeader.getLayoutParams();
        final float w = ivHeader.getLayoutParams().width;// 图片当前宽度
        final float h = ivHeader.getLayoutParams().height;// 图片当前高度
        final float newW = metric.widthPixels;// 图片原宽度
        final float newH = metric.widthPixels * 9 / 16;// 图片原高度
        // 设置动画
        anim = ObjectAnimator.ofFloat(0.0F, 1.0F).setDuration(200);
        anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                float cVal = (Float) animation.getAnimatedValue();
                lp.width = (int) (w - (w - newW) * cVal);
                lp.height = (int) (h - (h - newH) * cVal);
                ivHeader.setLayoutParams(lp);
            }
        });
        //开启动画
        anim.start();

    }