android - validateClientPermissionsLocked : Caller "package" cannot open camera "1" from background'

Question

当应用程序在后台时，尝试从前置摄像头拍摄照片。
我有以下代码在 Android 6 及更低版本中工作。

Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
cameraCount = Camera.getNumberOfCameras();
for (int camIdx = 0; camIdx < cameraCount; camIdx++) {
    Camera.getCameraInfo(camIdx, cameraInfo);
    if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
        myCamera = Camera.open(camIdx);
    }
}

仅当应用程序在前台时，这才适用于 Android 7 及更高版本。如果应用程序在后台，则会显示以下错误:

W/CameraBase: An error occurred while connecting to camera 1: Status(-8): '6: validateClientPermissionsLocked:915: Caller "packagename" (PID 10152, UID 32606) cannot open camera "1" from background'

W/System.err: java.lang.RuntimeException: Fail to connect to camera service

W/System.err:     at android.hardware.Camera.<init>(Camera.java:546)

W/System.err:     at android.hardware.Camera.open(Camera.java:392)

W/System.err:     at com.tracking_smartphone.TakePictureActivity.takePictureNoPreview(TakePictureActivity.java:77)

W/System.err:     at com.tracking_smartphone.TakePictureActivity.onCreate(TakePictureActivity.java:46)

W/System.err:     at android.app.Activity.performCreate(Activity.java:7144)

W/System.err:     at android.app.Activity.performCreate(Activity.java:7135)

W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)

W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2894)

W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3049)

W/System.err:     at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)

W/System.err:     at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)

W/System.err:     at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)

W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1809)

W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:106)

W/System.err:     at android.os.Looper.loop(Looper.java:193)

W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6680)

W/System.err:     at java.lang.reflect.Method.invoke(Native Method)

W/System.err:     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)

W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

该代码在从 JobService 调用的 Activity 中调用。

Answer 1

Android 文档 says :

Foreground Services Requirement - When does your app interact with the camera? On Android 9 (API level 28) and later, apps running in the background cannot access the camera. Therefore, you should use the camera either when your app is in the foreground or as part of a foreground service.

因此，如果您希望能够在后台与相机进行交互，您需要通过所谓的“前台服务”来进行，该服务基本上是一个带有通知的后台服务，该通知告诉用户它何时处于 Activity 状态并具有持久性通知。见foreground service documentation举些例子。