Question

我有一个地图活动，用于以全屏模式显示地图：

public class MapActivity extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(new Panel(this));
}

public class Panel extends SurfaceView implements SurfaceHolder.Callback {

public Panel(Context context) {
        super(context);
        getHolder().addCallback(this);

        // initiate new thread for drawing
        _thread = new CanvasThread(getHolder(), this);
}

// start thread 
@Override
public void surfaceCreated(SurfaceHolder holder) {
        CanvasThread.setRunning(true);
        _thread.start();
}

// start drawing objects on canvas
@Override
public void onDraw(Canvas canvas) {
        super.onDraw(canvas);
     /* several canvas operations ...
     */
}

// Thread specific class
static class CanvasThread extends Thread {
    private SurfaceHolder _surfaceHolder;
    private Panel _panel;
    private static boolean _run = false;

    public CanvasThread(SurfaceHolder surfaceHolder, Panel panel) {
        _surfaceHolder = surfaceHolder;
        _panel = panel;
    }

    public static void setRunning(boolean run) {
        _run = run;
    }

    @Override
    public void run() {
        Canvas c;
        Log.d("Thread", "start");
        while (_run) {
            c = null;
            try {
                c = _surfaceHolder.lockCanvas(null);
                synchronized (_surfaceHolder) {
                    Log.d("Thread", "Canvas c init");
                    _panel.onDraw(c);
                }
            } finally {
                // do this in a finally so that if an exception is thrown
                // during the above, we don't leave the Surface in an
                // inconsistent state
                if (c != null) {
                    _surfaceHolder.unlockCanvasAndPost(c);
                }
            }
        }
    }
}
}

现在，我想使用同一个类在SurfaceView元素中的其他活动中显示我的地图。因此，我尝试在一个新的Activity中使用SurfaceView元素，如下所示：

....
Panel surface = new KarteActivity().new Panel(this);
    surface._thread.start();
    CanvasThread.setRunning(true);
    LinearLayout midLL = new LinearLayout(this);

    midLL.findViewById(R.id.surfaceView1);
    midLL.addView(surface);

这会导致nullpointer异常，因为canvas是null。在全屏模式下，我没有错误。我的错是什么？

解决此类问题的常用方法如何？

Answer 1

好的，最后我自己得到了答案:)以下是解决方案：

包含SurfaceView元素的活动必须移交SurfaceHolder

SurfaceView surface = (SurfaceView) findViewById(R.id.surfaceView1);
SurfaceHolder surfaceHolder = surface.getHolder();
Panel panel = new Panel(this,surfaceHolder);

表面类必须在其构造函数中初始化曲面，并且线程将在创建曲面时启动。

public class Panel extends SurfaceView implements SurfaceHolder.Callback {

public Panel(Context context, SurfaceHolder surfaceHolder) {
    super(context);
    surfaceHolder.addCallback(this);
}

// start thread 
@Override
public void surfaceCreated(SurfaceHolder surfaceHolder) {
    // initiate new thread for drawing
    _thread = new CanvasThread(surfaceHolder, this);
    _thread.setRunning(true);
    _thread.start();
}

// start drawing objects on canvas
@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
 /* several canvas operations ...
 */
}

// Thread specific class
class CanvasThread extends Thread {
    private SurfaceHolder _surfaceHolder;
    private Panel _panel;
    private boolean _run = false;

    public CanvasThread(SurfaceHolder surfaceHolder, Panel panel) {
        _surfaceHolder = surfaceHolder;
        _panel = panel;
    }

    public void setRunning(boolean run) {
        _run = run;
    }

    @Override
    public void run() {
        Canvas c;
        Log.d("Thread", "start");
        while (_run) {
            c = null;
            try {
                c = _surfaceHolder.lockCanvas(null);
                synchronized (_surfaceHolder) {
                    Log.d("Thread", "Canvas c init");
                    _panel.onDraw(c);
                }
            } finally {
                // do this in a finally so that if an exception is thrown
                // during the above, we don't leave the Surface in an
                // inconsistent state
                if (c != null) {
                    _surfaceHolder.unlockCanvasAndPost(c);
                }
            }
        }
    }
}
}

这对我有用，但我决定将类Panel从MapActivity类中分离出来（在我的问题中显示）

如何将现有的全屏面板放入普通Activity的SurfaceView元素中

1 个答案: