Question

我正在尝试请求相机权限以在我的Android应用中使用Google OCR，但是在大多数设备上，它在安装时崩溃。

我读过类似的文章，说这是由于将空上下文传递到ContextCompat.checkSelfPermission()中引起的，但是我看不到上下文将如何为空。

这是我的代码：

    @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实现了SurfaceHolder.Callback，这是实际初始化相机的地方。

这是例外：

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)

Answer 1

通过查看源代码，我最大的猜测是您最终将null作为要传递给String[]的{{1}}中的条目之一。

那可能是由于您如何在数组和列表之间进行转换。特别是，ActivityCompat.requestPermissions()有点吓人，因为您正试图重用作为参数传入的permissionsToRequest.toArray(permissions)。另外，as Andy pointed out，String[]将未使用的数组元素设置为toArray()。

我将像here一样分配一个新的null：

String[]

请求摄影机权限会导致String.equals

1 个答案: