Question

我发生了一个非常不寻常的错误，从未经历过这样的事情。

我在我的应用程序中使用片段。在Android M及以上我使用的应用程序，当我最小化应用程序并授予权限并再次恢复应用程序时，应用程序崩溃，因为我试图在主要活动中使用对象，但我得到null。但是，当我这样做并删除许可时，我不会崩溃。

只有在应用程序最小化时尝试授予权限时才会发生这种情况。如果我关闭应用程序并授予权限并再次启动应用程序，那么我不会遇到任何此类问题。

我收到错误的行：

Screen_title.setText("Survey No. " + mainActivity.currentTask.farmerData.farms.survey_number);

其中“mainActivity.currentTask”为空。

Logcat：

04-13 10:44:26.226 16742-16742/com.app.farmtrace.fieldagent E/AndroidRuntime: FATAL EXCEPTION: main Process: com.app.farmtrace.fieldagent, PID: 16742 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.farmtrace.fieldagent/com.app.farmtrace.fieldagent.Activity.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'com.app.farmtrace.fieldagent.Data.Farmer_Data.FarmerData com.app.farmtrace.fieldagent.Data.Task.farmerData' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3256)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3352)
    at android.app.ActivityThread.access$1100(ActivityThread.java:223)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:158)
    at android.app.ActivityThread.main(ActivityThread.java:7231)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
    Caused by: java.lang.NullPointerException: Attempt to read from field 'com.app.farmtrace.fieldagent.Data.Farmer_Data.FarmerData com.app.farmtrace.fieldagent.Data.Task.farmerData' on a null object reference
    at com.app.farmtrace.fieldagent.Fragment.Farmer_Details.bindView(Farmer_Details.java:88)
    at com.app.farmtrace.fieldagent.Fragment.Farmer_Details.onViewCreated(Farmer_Details.java:64)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1315)
    at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1523)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1585)
    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:2832)
    at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:201)
    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:603)
    at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:181)
    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1266)
    at android.app.Activity.performStart(Activity.java:6916)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3219)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3352) 
    at android.app.ActivityThread.access$1100(ActivityThread.java:223) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:158) 
    at android.app.ActivityThread.main(ActivityThread.java:7231) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

当应用程序在后台运行时，我们无法给出权限，这就是应用程序崩溃的原因。当应用程序在后台运行时，系统已经为它占用了一些资源，所以当app在后台运行时我们无法获得它的权限。

Answer 2

private Context mContext;
 private HomeTab mActivity;

 mActivity = ((HomeTab) getActivity());
 mContext = ((HomeTab) getContext());

检查片段中的权限，如下所示，传递您的活动和上下文

if (ActivityCompat.checkSelfPermission(getContext(),
            android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
            ActivityCompat.checkSelfPermission(getContext(),
                    android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(getActivity(),
                new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION,
                        android.Manifest.permission.ACCESS_FINE_LOCATION},
                REQUEST_LOCATION);
    } else {
        Log.e("DB", "PERMISSION GRANTED");
    }

更改权限时崩溃

2 个答案: