我有一个以全屏模式显示 map 的 map Activity :
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,我想使用相同的类在 SurfaceView 元素内的其他 Activity 中显示我的 map 。因此,我尝试在新的 Activity 中获取 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);
这会导致空指针异常,因为 Canvas 为空。在全屏模式下我没有错误。 我的错误是什么?
解决此类问题的常用方法是什么?
最佳答案
好的,最后我自己得到了答案 :) 这是解决方案:
包含SurfaceView元素的activity必须交出SurfaceHolder
SurfaceView surface = (SurfaceView) findViewById(R.id.surfaceView1); SurfaceHolder surfaceHolder = surface.getHolder(); Panel panel = new Panel(this,surfaceHolder);
Surface 类必须在其构造函数中初始化 Surface,线程将在创建 Surface 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 Panel 类与 MapActivity 类分开(在我的问题中显示)
关于android - 如何将现有的全屏面板放入普通 Activity 的 SurfaceView 元素中,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13544377/