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POHow SurfaceHolder callbacks are related to Activity lifecycle?
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copied!<p>I've been trying to implement an application that requires camera preview on a surface. As I see the things, both activity and surface lifecycles consist of the following states:</p> <ol> <li>When I first launch my Activity: <code>onResume()->onSurfaceCreated()->onSurfaceChanged()</code></li> <li>When I leave my Activity: <code>onPause()->onSurfaceDestroyed()</code></li> </ol> <p>In this scheme, I can do corresponding calls like open/release camera and start/stop preview in <code>onPause/onResume</code> and <code>onSurfaceCreated()/onSurfaceDestroyed()</code>.</p> <p>It works fine, unless I lock the screen. When I launch the app, then lock the screen and unlock it later I see:</p> <p><code>onPause()</code> - and nothing else after the screen is locked - then <code>onResume()</code> after unlock - and no surface callbacks after then. Actually, <code>onResume()</code> is called after the power button is pressed and the screen is on, but the lock screen is still active, so, it's before the activity becomes even visible.</p> <p>With this scheme, I get a black screen after unlock, and no surface callbacks are called.</p> <p>Here's a code fragment that doesn't involve actual work with the camera, but the <code>SurfaceHolder</code> callbacks. The issue above is reproduced even with this code on my phone (callbacks are called in a normal sequence when you press "Back" button, but are missing when you lock the screen):</p> <pre><code>class Preview extends SurfaceView implements SurfaceHolder.Callback { private static final String tag= "Preview"; public Preview(Context context) { super(context); Log.d(tag, "Preview()"); SurfaceHolder holder = getHolder(); holder.addCallback(this); holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); } public void surfaceCreated(SurfaceHolder holder) { Log.d(tag, "surfaceCreated"); } public void surfaceDestroyed(SurfaceHolder holder) { Log.d(tag, "surfaceDestroyed"); } public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { Log.d(tag, "surfaceChanged"); } } </code></pre> <p>Any ideas on why the surface remains undestroyed after the Activity is paused? Also, how do you handle camera lifecycle in such cases?</p>

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