Android RunTime Berechtigungen

Question

Ich versuche Laufzeitberechtigungen hinzuzufügen, um eine App für API 23+ kompatibel zu machen. Ich ging durch die documentation aber als ich zählen nur die folgende Zeile

private final int hasWriteFilePermission = ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.WRITE_EXTERNAL_STORAGE);,

meine App stürzt ab und ich bekomme die folgende Fehlermeldung:

07-10 20:54:15.571 31479-31479/com.ibm.watson.developer_cloud.android.examples E/AndroidRuntime: FATAL EXCEPTION: main 
                          Process: com.ibm.watson.developer_cloud.android.examples, PID: 31479 
                          java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ibm.watson.developer_cloud.android.examples/com.ibm.watson.developer_cloud.android.examples.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference 
                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254) 
                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350) 
                           at android.app.ActivityThread.access$1100(ActivityThread.java:222) 
                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795) 
                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                           at android.os.Looper.loop(Looper.java:158) 
                           at android.app.ActivityThread.main(ActivityThread.java:7229) 
                           at java.lang.reflect.Method.invoke(Native Method) 
                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
                           Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference 
                           at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:337) 
                           at android.widget.AbsSpinner.setAdapter(AbsSpinner.java:115) 
                           at android.widget.Spinner.setAdapter(Spinner.java:554) 
                           at com.ibm.watson.developer_cloud.android.examples.MainActivity$FragmentTabSTT.addItemsOnSpinnerModels(MainActivity.java:566) 
                           at com.ibm.watson.developer_cloud.android.examples.MainActivity$FragmentTabSTT.onCreateView(MainActivity.java:190) 
                           at android.app.Fragment.performCreateView(Fragment.java:2281) 
                           at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:983) 
                           at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1163) 
                           at android.app.BackStackRecord.run(BackStackRecord.java:793) 
                           at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1552) 
                           at android.app.FragmentController.execPendingActions(FragmentController.java:325) 
                           at android.app.Activity.performStart(Activity.java:6914) 
                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3217) 
                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)  
                           at android.app.ActivityThread.access$1100(ActivityThread.java:222)  
                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)  
                           at android.os.Handler.dispatchMessage(Handler.java:102)  
                           at android.os.Looper.loop(Looper.java:158)  
                           at android.app.ActivityThread.main(ActivityThread.java:7229)  
                           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)  

Mein Code ist wie folgt:

public static class FragmentTabSTT extends Fragment implements ISpeechToTextDelegate { 
    . 
    . 
    . 
@Override 
    public void onAttach(Context context) { 
     super.onAttach(context); 

     Activity a; 

     if (context instanceof Activity){ 
      a = (Activity) context; 
     } 

    } 



    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
            Bundle savedInstanceState) { 
    . 
    . 
    . 
    } 
    . 
    . 
    . 
     // One method that requires permission 
public ArrayList<String> GetFiles(String DirectoryPath) { 

     int hasReadFilesPermission = ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.READ_EXTERNAL_STORAGE); 

     if (hasReadFilesPermission != PackageManager.PERMISSION_GRANTED) { 
      if (!shouldShowRequestPermissionRationale(permission.READ_EXTERNAL_STORAGE)) { 
       showMessageOKCancel("You must give permission to read from storage.", 
         new DialogInterface.OnClickListener() { 
          @Override 
          public void onClick(DialogInterface dialog, int which) { 
           requestPermissions(new String[] {permission.READ_EXTERNAL_STORAGE}, 
             REQUEST_CODE_ASK_PERMISSIONS); 
          } 
         }); 
       return null; 
      } 

      requestPermissions(new String[] {permission.READ_EXTERNAL_STORAGE}, 
        REQUEST_CODE_ASK_PERMISSIONS); 
      return null; 
     } 
     ArrayList<String> MyFiles = new ArrayList<String>(); 
     File f = new File(DirectoryPath); 

     f.mkdirs(); 
     File[] files = f.listFiles(); 
     if (files.length == 0) 
      return null; 
     else { 
      for (int i=0; i<files.length; i++) 
       MyFiles.add(files[i].getName()); 
     } 

     return MyFiles; 
    } 
} 

Wie sollte? d Ich überprüfe innerhalb des Fragments die Berechtigung? Was verursacht diesen Fehler? Wie löse ich dieses Problem? Vielen Dank!

Answer 1

getActivity() gibt null zurück, wenn ein Fragment zuerst erstellt wird (d. H. Bevor onAttach() aufgerufen wird).

Sie sollten nach Berechtigungen suchen, bevor Sie sie benötigen, anstatt sie in einer letzten Klassenvariablen zu speichern.

Answer 2

Sie es nicht in einer statischen Variablen nennen:

@Override 
onViewCreated(Bundle savedInstanceState) { 
    String[] permissions = new String[]{Manifest.permission.SEND_SMS}; 
    ActivityCompat.requestPermissions(getActivity(), permissions, PERMISSIONS_CODE); 
} 

einen Listener für Berechtigungen hinzufügen:

@Override 
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) { 
    super.onRequestPermissionsResult(requestCode, permissions, grantResults); 
    // do stuff 
} 

Und Sie werden von AppCompatFragment erben müssen.