Android:当 Activity 进入后台时如何使用相机？

Question

当我的 Activity 进入后台时，如何释放相机？ (例如按手机上的待机键)

    public void onPause(){
    super.onPause();
    if (cam != null) {
        cam.stopPreview();
        cam.release();
        cam = null;
    }
}

@Override
protected void onResume(){
 super.onResume();
    rLayout = (RelativeLayout) findViewById (R.id.layout_background);
    cam = Camera.open();  
    cam.startPreview();
    p = cam.getParameters();
}

日志:

02-20 11:46:40.040: E/AndroidRuntime(26439): FATAL EXCEPTION: main
02-20 11:46:40.040: E/AndroidRuntime(26439): java.lang.RuntimeException: Unable to resume activity {spicysoftware.spicytaschenlampe/spicysoftware.spicytaschenlampe.FlashLight}: java.lang.RuntimeException: Fail to connect to camera service
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2616)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2644)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2130)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.os.Looper.loop(Looper.java:137)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.main(ActivityThread.java:4898)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at java.lang.reflect.Method.invokeNative(Native Method)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at java.lang.reflect.Method.invoke(Method.java:511)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at dalvik.system.NativeStart.main(Native Method)
02-20 11:46:40.040: E/AndroidRuntime(26439): Caused by: java.lang.RuntimeException: Fail to connect to camera service
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.hardware.Camera.native_setup(Native Method)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.hardware.Camera.<init>(Camera.java:353)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.hardware.Camera.open(Camera.java:330)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at spicysoftware.spicytaschenlampe.FlashLight.onResume(FlashLight.java:182)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1199)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.Activity.performResume(Activity.java:5280)
02-20 11:46:40.040: E/AndroidRuntime(26439):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2606)
02-20 11:46:40.040: E/AndroidRuntime(26439):    ... 12 more

这是它的工作原理:

    public void onPause(){
    super.onPause();
    Log.v("OnPause", "True");
    if (cam != null) {
        Log.v("OnPause", "Cam isn't null");
        cam.stopPreview();
        Log.v("OnPause", "CamPreview stopped");
        cam.release();
        Log.v("OnPause", "CamReleased");
        cam = null;
        Log.v("OnPause", "Cam is null");
    }
}


@Override
protected void onResume(){
 super.onResume();
 Log.v("OnResume", "True");
    if(cam != null){
        Log.v("OnResume", "Camera is in use");
    } else {
        Log.v("OnResume", "Camera isn't in use");
        rLayout = (RelativeLayout) findViewById (R.id.layout_background);
        cam = Camera.open();  
        Log.v("OnResume", "Camera has been opened");
        cam.startPreview();
        Log.v("OnResume", "CamPreview started");
        p = cam.getParameters();
        Log.v("OnResume", "Wrote parameters to variable p");
    }
}

在 onResume 中打开相机会使应用程序崩溃。

最好的问候MSeiz5

Answer 1

在 onResume 中重新打开并重置相机。

@Override
protected void onResume(){
 super.onResume();
 camera = Camera.open();

 // We resumed so lock the camera
 Camera.Parameters params = camera.getParameters();

 params.setFlashMode(Parameters.FLASH_MODE_ON);
 //params.setFocusMode(Parameters.FOCUS_MODE_AUTO);
 //params.setWhiteBalance(Parameters.WHITE_BALANCE_AUTO);
 params.setJpegQuality(100);

 camera.setParameters(params);
 ImageView overlay = (ImageView) findViewById(R.id.ImageView01);
 overlay.bringToFront();
}