android camera release error from PreviewCallback

So I've read over the Camera API and couldn't find anything on this. I'm using the Camera to grab frames and it works perfectly, until I try to release the camera. I replicated the error in one sequence of calls:

camera = Camera.open();
camera.setPreviewDisplay(getHolder());
Parameters params = camera.getParameters();
List<Size> ls = params.getSupportedPreviewSizes();
Size size = ls.get(1);
this.width = size.width;
this.height = size.height;
params.setPreviewSize(size.width, size.height);
camera.setParameters(params);
camera.setDisplayOrientation(90);
camera.setPreviewCallback(this);
camera.startPreview();
camera.stopPreview();
camera.release();

The error I get is

03-22 13:31:42.592: E/AndroidRuntime(14152): java.lang.RuntimeException: Method called after release()
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.hardware.Camera.setHasPreviewCallback(Native Method)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.hardware.Camera.access$600(Camera.java:114)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.hardware.Camera$EventHandler.handleMessage(Camera.java:545)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.os.Looper.loop(Looper.java:130)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at android.app.ActivityThread.main(ActivityThread.java:3684)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at java.lang.reflect.Method.invokeNative(Native Method)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at java.lang.reflect.Method.invoke(Method.java:507)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:845)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:603)
03-22 13:31:42.592: E/AndroidRuntime(14152):    at dalvik.system.NativeStart.main(Native Method)

So whatever is going on is not in one of my functions. If I comment out the camera.setPreviewCallback(this); then this error does not appear, but I obviously lose my callback, which is the whole point of including the camera in my app.

回答1:

You have to unset preview callback before camera.release(), after camera.stopPreview():

camera.setPreviewCallback(null);

Otherwise it might get called after camera has been released.

回答2:

As a side note, a complete releaseCamera method looks like:

// release Camera for other applications
private void releaseCamera() {
    // check if Camera instance exists
    if (mCamera != null) {
        sPreviewing = false;
        // first stop preview
        mCamera.stopPreview();
        // then cancel its preview callback
        mCamera.setPreviewCallback(null);
        // and finally release it
        mCamera.release();
        // sanitize you Camera object holder
        mCamera = null;
    }
}