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I'm trying to request camera permissions to use Google OCR in my Android app, but on most devices it crashes on install.

I've read similar posts that say this is caused by a null context being passed into ContextCompat.checkSelfPermission(), but I can't see how the context would be null.

Here is my code:

    @Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);



    StrictMode.VmPolicy.Builder builder = new StrictMode.VmPolicy.Builder();

    StrictMode.setVmPolicy(builder.build());



    surfaceView = findViewById(R.id.surfaceView);



    if (checkForPermissions(Manifest.permission.CAMERA,

            Manifest.permission.READ_EXTERNAL_STORAGE,

            Manifest.permission.INTERNET)) {

        surfaceView.getHolder().addCallback(new SurfaceCallback());

    }

}

...

private boolean checkForPermissions(String ... permissions) {

    List<String> permissionsToRequest = new ArrayList<>(Arrays.asList(permissions));



    for (Iterator<String> it = permissionsToRequest.iterator(); it.hasNext();) {

        if (ContextCompat.checkSelfPermission(this, it.next()) == PackageManager.PERMISSION_GRANTED) {

            it.remove();

        }

    }

    if (permissionsToRequest.isEmpty()) {

        return true;

    }



    ActivityCompat.requestPermissions(MainActivity.this, permissionsToRequest.toArray(permissions), 0);

    return false;

}



@Override

public void onRequestPermissionsResult(int requestCode,

                                       @NonNull String permissions,

                                       @NonNull int results) {

    if (requestCode != 0) {

        return;

    }



    for (int i = 0; i < results.length; i++) {

        if (results[i] != PackageManager.PERMISSION_GRANTED && permissions[i] != null) {

            AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create();

            alertDialog.setTitle("Permissions needed");

            alertDialog.setMessage("This app requires camera permissions to function properly.");

            alertDialog.setButton(AlertDialog.BUTTON_POSITIVE, "OK",

                    new DialogInterface.OnClickListener() {

                        public void onClick(DialogInterface dialog, int which) {

                            dialog.dismiss();

                            ActivityCompat.requestPermissions(MainActivity.this,

                                    new String {

                                        Manifest.permission.CAMERA,

                                        Manifest.permission.READ_EXTERNAL_STORAGE,

                                        Manifest.permission.INTERNET

                                    },

                                    0);

                        }

                    });

            alertDialog.show();

            return;

        }

    }

    surfaceView.getHolder().addCallback(new SurfaceCallback());

}

SurfaceCallback implements SurfaceHolder.Callback and that's where the camera is actually initialized.

This is the exception:

4606/? E/AndroidRuntime: FATAL EXCEPTION: main

Process: com.google.android.packageinstaller, PID: 4606

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.google.android.packageinstaller/com.android.packageinstaller.permission.ui.GrantPermissionsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)

at android.app.ActivityThread.-wrap12(ActivityThread.java)

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)

at android.os.Handler.dispatchMessage(Handler.java:102)

at android.os.Looper.loop(Looper.java:154)

at android.app.ActivityThread.main(ActivityThread.java:6077)

at java.lang.reflect.Method.invoke(Native Method)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference

at com.android.packageinstaller.permission.ui.GrantPermissionsActivity.computePermissionGrantState(GrantPermissionsActivity.java:314)

at com.android.packageinstaller.permission.ui.GrantPermissionsActivity.updateDefaultResults(GrantPermissionsActivity.java:363)

at com.android.packageinstaller.permission.ui.GrantPermissionsActivity.onCreate(GrantPermissionsActivity.java:122)

at android.app.Activity.performCreate(Activity.java:6662)

at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 

at android.app.ActivityThread.-wrap12(ActivityThread.java) 

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 

at android.os.Handler.dispatchMessage(Handler.java:102) 

at android.os.Looper.loop(Looper.java:154) 

at android.app.ActivityThread.main(ActivityThread.java:6077) 

at java.lang.reflect.Method.invoke(Native Method) 

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756) 

By looking at the source code, my best guess is that you are winding up with null as one of the entries in the String that you are passing to ActivityCompat.requestPermissions().

That might be due to something with how you are converting between arrays and lists. In particular, permissionsToRequest.toArray(permissions) is kinda scary, as you are trying to reuse a String that is passed in as a parameter. Plus, as Andy pointed out, toArray() sets unused array elements to null.

I'd allocate a fresh String, as I do here:

  private boolean hasPermission(String perm) {

    return(ContextCompat.checkSelfPermission(this, perm)==

      PackageManager.PERMISSION_GRANTED);

  }



  private String netPermissions(String wanted) {

    ArrayList<String> result=new ArrayList<String>();



    for (String perm : wanted) {

      if (!hasPermission(perm)) {

        result.add(perm);

      }

    }



    return(result.toArray(new String[result.size()]));

  }