Android 实现可拖动的ImageView

代码实现：

public class DraggableImageView extends AppCompatImageView {

    private float lastTouchX;
    private float lastTouchY;

    public DraggableImageView(Context context) {
        super(context);
        init();
    }

    public DraggableImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public DraggableImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        setClickable(true);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        final int action = event.getActionMasked();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                lastTouchX = event.getRawX();
                lastTouchY = event.getRawY();
                break;

            case MotionEvent.ACTION_MOVE:
                float x = event.getRawX();
                float y = event.getRawY();

                x = Math.max(0,x);
                y = Math.max(0,y);


                float dx = x - lastTouchX;
                float dy = y - lastTouchY;
				//边界控制
                ViewGroup pa = (ViewGroup) getParent();
                float lx = Math.max(0,dx+getX());
                float ly = Math.max(0,dy+getY());
                lx = Math.min(lx,pa.getWidth()-getWidth());
                ly = Math.min(ly,pa.getHeight()-getHeight());

                setX(lx);
                setY(ly);



                lastTouchX = x;
                lastTouchY = y;
                break;

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                break;

            case MotionEvent.ACTION_POINTER_UP:

                lastTouchX = event.getRawX();
                lastTouchY = event.getRawX();
                break;
        }
        return true;
    }
}