Question

当我在屏幕上移动手指时，当我试图绘制路径时，我的应用程序强制关闭。代码开始绘制路径中的一些行，但随后强制关闭。我做错了什么？

MainActivity类中的OnTouchListener：

    @Override
public boolean onTouch(View v, MotionEvent event) {

    switch (event.getAction()) {

    case MotionEvent.ACTION_DOWN:
        gameLoop.touchDownX = event.getX();
        gameLoop.touchDownY = event.getY();
        break;

    case MotionEvent.ACTION_MOVE:
        Point point = new Point();
        point.x = (int) event.getX();
        point.y = (int) event.getY();
        gameLoop.addPoints(point);
        gameLoop.startDrawLine = true;
        break;

    case MotionEvent.ACTION_UP:
        gameLoop.touchUpX = event.getX();
        gameLoop.touchUpY = event.getY();
        gameLoop.touchActionUp = true;
        break;
    }

    return true; 
}

GameLoop类中的draw方法：

    // Method to draw objects
private void drawObjects(Canvas canvas) {

    // Clear screen with black color
    canvas.drawRGB(0, 0, 0);

    // Draw line
    if(startDrawLine) {

        // Set properties to Paint object
        paint.setColor(Color.WHITE);
        paint.setStrokeWidth(5);
        paint.setStyle(Paint.Style.STROKE);
        paint.setAntiAlias(true);

        // Draw path
        path.moveTo(touchDownX, touchDownY);

        for(Point point: points) {
            path.lineTo(point.x, point.y);
            canvas.drawPath(path, paint);
        }
        path.reset();
    }

LogCat信息：

04-28 11:54:23.155: W/dalvikvm(2896): threadid=10: thread exiting with uncaught  exception (group=0x40018578)
04-28 11:54:23.155: E/AndroidRuntime(2896): FATAL EXCEPTION: Thread-11
04-28 11:54:23.155: E/AndroidRuntime(2896): java.util.ConcurrentModificationException
04-28 11:54:23.155: E/AndroidRuntime(2896):     at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:576)
04-28 11:54:23.155: E/AndroidRuntime(2896):     at com.androidTest.mergemania.GameLoop.drawObjects(GameLoop.java:251)
04-28 11:54:23.155: E/AndroidRuntime(2896):     at com.androidTest.mergemania.GameLoop.run(GameLoop.java:216)
04-28 11:54:23.155: E/AndroidRuntime(2896):     at java.lang.Thread.run(Thread.java:1019)

Answer 1

是drawObjects中的所有代码吗？ LogCat告诉我们您在迭代时修改列表。我希望你有这样的代码打破：

    for(Point point: points) {
        path.lineTo(point.x, point.y);
        canvas.drawPath(path, paint);
        points.remove(point); // this line added
    }

修改

哦，你可能正在使用SurfaceView并在一个单独的线程中绘图。在这种情况下，您需要将调用与点列表同步。也许使用CopyOnWriteArrayList。

请阅读SurfaceView上的线索。

<强> EDIT2：

这样的东西应该可行，但我真的不会在生产代码中使用它，因为它会阻塞线程。您需要拥有非常少量的代码（就执行时间而言）才能使线程高效工作。（添加了4行，注释了this line added）。

@Override public boolean onTouch(View v, MotionEvent event) { synchronized (gameLoop) { // this line added switch (event.getAction()) { case MotionEvent.ACTION_DOWN: gameLoop.touchDownX = event.getX(); gameLoop.touchDownY = event.getY(); break; case MotionEvent.ACTION_MOVE: Point point = new Point(); point.x = (int) event.getX(); point.y = (int) event.getY(); gameLoop.addPoints(point); gameLoop.startDrawLine = true; break; case MotionEvent.ACTION_UP: gameLoop.touchUpX = event.getX(); gameLoop.touchUpY = event.getY(); gameLoop.touchActionUp = true; break; } } // this line added return true; }

和此：

// Method to draw objects private void drawObjects(Canvas canvas) { synchronized (this) { // this line added // Clear screen with black color canvas.drawRGB(0, 0, 0); // Draw line if(startDrawLine) { // Set properties to Paint object paint.setColor(Color.WHITE); paint.setStrokeWidth(5); paint.setStyle(Paint.Style.STROKE); paint.setAntiAlias(true); // Draw path path.moveTo(touchDownX, touchDownY); for(Point point: points) { path.lineTo(point.x, point.y); canvas.drawPath(path, paint); } path.reset(); } } // this line added

从ArrayList绘制路径不起作用

1 个答案: