如何在Android Studio中修复“ RuntimeException：无法恢复活动...”

Question

我已经开始运行我的应用程序，遇到了这个问题

RuntimeException: Unable to resume activity

但是我发现了问题。这是在我的方法protected void onPause()中。如果我删除了camera = null行，它不会改变。

我试图修复，但我做不到

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

    @Override
    protected void onPause() {
        super.onPause();

        if (camera != null) {
            camera.setPreviewCallback(null);
            camera.stopPreview();
            camera.release();
            camera = null;
        }
    }

日志是：

java.lang.RuntimeException: Unable to resume activity {com.example.scanera/com.example.scanera.MainActivity}: java.lang.RuntimeException: Fail to connect to camera service
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3502)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3542)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2790)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1523)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:163)
        at android.app.ActivityThread.main(ActivityThread.java:6238)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
     Caused by: java.lang.RuntimeException: Fail to connect to camera service
        at android.hardware.Camera.<init>(Camera.java:579)
        at android.hardware.Camera.open(Camera.java:419)
        at com.example.scanera.MainActivity.onResume(MainActivity.java:170)
        at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1270)
        at android.app.Activity.performResume(Activity.java:6981)
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3479)