Android实现view拖动到任意位置

本文实现：将图片任意拖动，如果拖动到正确位置则成功，若抬起手时时错误位置则自动回到原位。

定义

private ImageView img;
private ImageView imageView;

//容器的宽高，需要在屏幕绘制好之后才能获取
private int containerWidth;
    private int containerHeight;

    private float lastX, lastY;

//获取需要拖动到的正确位置
 private int[] imgPosition = new int[2];
    private int height;
    private int width;

在屏幕绘制好之后获取宽高和位置

@Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        // 这里来获取容器的宽和高
        if (hasFocus) {
            containerHeight = sunPage.getHeight();
            containerWidth = sunPage.getWidth();
        }

        //获取需要拖动到的正确位置，img处
        img.getLocationInWindow(imgPosition);
        height = img.getMeasuredHeight();
        width = img.getMeasuredWidth();
    }

手势事件

imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getActionMasked()) {
                    case MotionEvent.ACTION_DOWN:
                     //手指在屏幕位置getRawX() getRawY()
                        lastX = event.getRawX();
                        lastY = event.getRawY();
                        break;
                    case MotionEvent.ACTION_MOVE:
                    // 不要直接用getX和getY,这两个获取的数据已经是经过处理的,容易出现图片抖动的情况
            float distanceX = xx - event.getRawX();
            float distanceY = yy - event.getRawY();

            float nextY = imageView.getY() - distanceY;
            float nextX = imageView.getX() - distanceX;

            // 不能移出屏幕
            if (nextY < 0) {
                nextY = 0;
            } else if (nextY > containerHeight - imageView.getHeight()) {
                nextY = containerHeight - imageView.getHeight();
            }
            if (nextX < 0)
                nextX = 0;
            else if (nextX > containerWidth - imageView.getWidth())
                nextX = containerWidth - imageView.getWidth();

            // 属性动画移动
            ObjectAnimator y = ObjectAnimator.ofFloat(imageView, "y", imageView.getY(), nextY);
            ObjectAnimator x = ObjectAnimator.ofFloat(imageView, "x", imageView.getX(), nextX);

            animatorSet.playTogether(x, y);
            animatorSet.setDuration(0);
            animatorSet.start();
                        lastX = event.getRawX();
                        lastY = event.getRawY();
                        if (correct(lastX, lastY, imgPosition, m)) {
                            //正确后的事情
                        }
                        break;
                    case MotionEvent.ACTION_UP:
                     //抬起手后自动弹回原处，监听animatorSet
                        animatorSet.cancel();
                        break;
                }
                return true;
            }
        });

判断拖动是否正确，m是img的半径，拖动结合的难易可以自己调剂算法

//判断拖动是否正确，m是img的半径，拖动结合的难易可以自己调剂算法
private boolean correct(float x, float y, int[] a, int m) {
        float s = (float) Math.sqrt((x - a[0]) * (x - a[0]) + (y - a[1]) * (y - a[1]) - (x - a[0]) * (y - a[1]));
        if (s <= ActivityUtils.dip2px(HomeGameActivity.this, m)) {
            return true;
        }
        return false;
    }

监听animatorSet，cancle时imageview返回原处

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

            @Override
            public void onAnimationEnd(Animator animation) {
            }

            @Override
            public void onAnimationCancel(Animator animation) {
                imageView.setTranslationY(0);
          imageView.setTranslationX(0);
            }

            @Override
            public void onAnimationRepeat(Animator animation) {

            }
 });

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