Android单点触控技术，对图片进行平移，缩放，旋转操作

Android提供了多点触控的支持，可以实现图片的平移、缩放、旋转等操作。下面简单介绍一下单点触控实现图片操作的方法。

1. 平移操作

平移操作可以通过监听手指在屏幕上的移动来实现。在ImageView上监听ACTION_MOVE事件，根据手指移动的距离，更新图片的位置即可。

示例代码：

imageView.setOnTouchListener(new View.OnTouchListener() {
    private float lastX, lastY;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = event.getX();
                lastY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                float moveX = event.getX() - lastX;
                float moveY = event.getY() - lastY;
                imageView.scrollBy(-(int) moveX, -(int) moveY);
                lastX = event.getX();
                lastY = event.getY();
                break;
        }
        return true;
    }
});

2. 缩放操作

缩放操作可以通过手势缩放来实现。在ImageView上监听ACTION_MOVE事件，根据手势的缩放比例，更新图片的大小即可。

示例代码：

imageView.setOnTouchListener(new View.OnTouchListener() {
    private float lastX, lastY;
    private float scale = 1f;
    private float minScale = 0.5f;
    private float maxScale = 2f;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                lastX = event.getX();
                lastY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                if (event.getPointerCount() == 2) {
                    float distance = getDistance(event);
                    float diffScale = distance / lastDistance;
                    scale *= diffScale;
                    if (scale < minScale) {
                        scale = minScale;
                    }
                    if (scale > maxScale) {
                        scale = maxScale;
                    }
                    imageView.setScaleX(scale);
                    imageView.setScaleY(scale);
                    lastDistance = distance;
                } else {
                    float moveX = event.getX() - lastX;
                    float moveY = event.getY() - lastY;
                    imageView.scrollBy(-(int) moveX, -(int) moveY);
                    lastX = event.getX();
                    lastY = event.getY();
                }
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                lastDistance = getDistance(event);
                break;
        }
        return true;
    }

    private float lastDistance;
    private float getDistance(MotionEvent event) {
        float dx = event.getX(1) - event.getX(0);
        float dy = event.getY(1) - event.getY(0);
        return (float) Math.sqrt(dx * dx + dy * dy);
    }
});

3. 旋转操作

旋转操作可以通过手势旋转来实现。在ImageView上监听ACTION_MOVE事件，根据手势旋转的角度，更新图片的旋转角度即可。

示例代码：

imageView.setOnTouchListener(new View.OnTouchListener() {
    private float lastX, lastY;
    private float rotation = 0f;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                lastX = event.getX();
                lastY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                if (event.getPointerCount() == 2) {
                    float angle = getRotation(event);
                    rotation += angle;
                    imageView.setRotation(rotation);
                } else {
                    float moveX = event.getX() - lastX;
                    float moveY = event.getY() - lastY;
                    imageView.scrollBy(-(int) moveX, -(int) moveY);
                    lastX = event.getX();
                    lastY = event.getY();
                }
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                lastAngle = getAngle(event);
                break;
        }
        return true;
    }

    private float lastAngle;
    private float getAngle(MotionEvent event) {
        float dx = event.getX(1) - event.getX(0);
        float dy = event.getY(1) - event.getY(0);
        return (float) Math.toDegrees(Math.atan2(dy, dx));
    }
    private float getRotation(MotionEvent event) {
        float angle = getAngle(event);
        float diffAngle = angle - lastAngle;
        lastAngle = angle;
        return diffAngle;
    }
});

以上就是Android单点触控实现图片平移、缩放、旋转的方法。当然，还有更复杂的多点触控实现方式，可以满足更高级的交互需求。