Question

我试图在canvas上画一个正方形，但只运行MotionEvent.ACTION_DOWN，然后listener停止。

这个想法是当用户触摸屏幕时它获得x1和y1位置，每次onTouch被触发时，它必须将rect frim x1 y1绘制到当前位置，最后保存最后一个位置一旦用户离开屏幕，x2 y2。

我的代码如下所示：

surfaceView.setOnTouchListener(new View.OnTouchListener()
{
    @Override
    public boolean onTouch(View v, MotionEvent event)
    {
        holder = surfaceView.getHolder();
        canvas = holder.lockCanvas();
        if(event.getAction() == MotionEvent.ACTION_DOWN)
        {
            x1=event.getX();
            y1=event.getY();
        }
        else if(event.getAction() == MotionEvent.ACTION_UP)
        {
            x2=event.getX();
            y2=event.getY();
        }
        canvas.drawRect(x1, y1, event.getX(), event.getY(), paint);
        holder.unlockCanvasAndPost(canvas);
        return true;
    }
});

任何人都可以举个例子。

Answer 1

ACTION_UP从上面的代码触发。尝试下面的代码，您将看到日志。

我认为您的问题可能与您获得的观点有关。我不知道你是如何定义x1，y1，x2，y2但是当声明超出范围时它们必须是最终的。试试这个。

final SurfaceView s = (SurfaceView) findViewById(R.id.surface);

final RectF rect = new RectF();

s.setOnTouchListener(new OnTouchListener() {

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        SurfaceHolder holder = s.getHolder();
        Canvas canvas = holder.lockCanvas();

        if(event.getAction() == MotionEvent.ACTION_DOWN) {
            Log.d("action", "down");
            rect.left = event.getX();
            rect.top = event.getY();
        }
        if(event.getAction() == MotionEvent.ACTION_UP){
            Log.d("action", "up");
            rect.right = event.getX();
            rect.bottom = event.getY();

            Paint paint = new Paint();
            paint.setColor(Color.RED);
            canvas.drawRect(rect, paint);
        }

        holder.unlockCanvasAndPost(canvas);
        return true;
    }
});

Answer 2

尝试使用它。

surfaceView.setOnTouchListener(new View.OnTouchListener()
{
    @Override
    public boolean onTouch(View v, MotionEvent event)
    {

        if(event.getAction() == MotionEvent.ACTION_DOWN)
        {
            x1=event.getX();
            y1=event.getY();
        }
        else if(event.getAction() == MotionEvent.ACTION_UP)
        {
            x2=event.getX();
            y2=event.getY();

            holder = surfaceView.getHolder();
            canvas = holder.lockCanvas();
            canvas.drawRect(x1, y1, x2, y2, paint);
            holder.unlockCanvasAndPost(canvas);
        }

        return true;
    }
});

如果你移动手指，它会在你做的每一个动作中呼叫听众。所以这段代码

holder = surfaceView.getHolder();
canvas = holder.lockCanvas();

和此代码

canvas.drawRect(x1, y1, event.getX(), event.getY(), paint);
holder.unlockCanvasAndPost(canvas);

将被执行，也许这就是它停止的原因。

所以我将drawRect置于MotionEvent.ACTION_UP条件中，因此drawRect将执行一次。

MotionEvents未触发

2 个答案: