扩展上面mVck的答案，下面的逻辑确定是否“Never ask again”已经为给定的权限请求进行了检查:

bool bStorage = grantResults[0] == Permission.Granted;
bool bNeverAskForStorage =
    !bStorage && (
        _bStorageRationaleBefore == true  && _bStorageRationaleAfter == false ||
        _bStorageRationaleBefore == false && _bStorageRationaleAfter == false
    );

摘自下面(完整的例子见这个答案)

private bool _bStorageRationaleBefore;
private bool _bStorageRationaleAfter;        
private const int ANDROID_PERMISSION_REQUEST_CODE__SDCARD = 2;
//private const int ANDROID_PERMISSION_REQUEST_CODE__CAMERA = 1;
private const int ANDROID_PERMISSION_REQUEST_CODE__NONE = 0;

public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)
{
    base.OnRequestPermissionsResult(requestCode, permissions, grantResults);

    switch (requestCode)
    {
        case ANDROID_PERMISSION_REQUEST_CODE__SDCARD:               
            _bStorageRationaleAfter = ShouldShowRequestPermissionRationale(Android.Manifest.Permission.WriteExternalStorage);
            bool bStorage = grantResults[0] == Permission.Granted;
            bool bNeverAskForStorage =
                !bStorage && (
                    _bStorageRationaleBefore == true  && _bStorageRationaleAfter == false ||
                    _bStorageRationaleBefore == false && _bStorageRationaleAfter == false
                );      
            break;                
    }
}

private List<string> GetRequiredPermissions(out int requestCode)
{
    // Android v6 requires explicit permission granting from user at runtime for security reasons            
    requestCode = ANDROID_PERMISSION_REQUEST_CODE__NONE; // 0
    List<string> requiredPermissions = new List<string>();

    _bStorageRationaleBefore = ShouldShowRequestPermissionRationale(Android.Manifest.Permission.WriteExternalStorage);
    Permission writeExternalStoragePerm = ApplicationContext.CheckSelfPermission(Android.Manifest.Permission.WriteExternalStorage);
    //if(extStoragePerm == Permission.Denied)
    if (writeExternalStoragePerm != Permission.Granted)
    {
        requestCode |= ANDROID_PERMISSION_REQUEST_CODE__SDCARD;
        requiredPermissions.Add(Android.Manifest.Permission.WriteExternalStorage);
    }

    return requiredPermissions;
}

protected override void OnCreate(Bundle savedInstanceState)
{
    base.OnCreate(savedInstanceState);

        // Android v6 requires explicit permission granting from user at runtime for security reasons
        int requestCode;
        List<string> requiredPermissions = GetRequiredPermissions(out requestCode);
        if (requiredPermissions != null && requiredPermissions.Count > 0)
        {
            if (requestCode >= ANDROID_PERMISSION_REQUEST_CODE__SDCARD)                    
            {
                _savedInstanceState = savedInstanceState;
                RequestPermissions(requiredPermissions.ToArray(), requestCode);
                return;
            }
        }
    }            

    OnCreate2(savedInstanceState);
}

请不要为这个解决办法向我扔石头。

这是可行的，但有点“俗气”。

当调用requestPermissions时，注册当前时间。

        mAskedPermissionTime = System.currentTimeMillis();

然后在onRequestPermissionsResult中

如果结果不允许，请再次检查时间。

 if (System.currentTimeMillis() - mAskedPermissionTime < 100)

由于用户不可能那么快地点击拒绝按钮，我们知道他选择了“永不再问”，因为回调是即时的。

使用风险自负。

我有点晚了，我也遇到过类似的问题。解决此问题如下

假设您需要位置权限

请求权限启动器

private final ActivityResultLauncher<String> requestPermissionLauncher =
      registerForActivityResult(
          new RequestPermission(),
          isGranted -> {
            if (isGranted) {
              // Permission is granted go ahead
            } else {
              shouldShowRequestPermissionRationale();
            }
          });

权限检查

  private boolean hasPermissions() {
        if (checkSelfPermission(requireActivity(), ACCESS_FINE_LOCATION) == PERMISSION_GRANTED) {
          // Permission is granted go ahead
        } else {
          requestPermissionLauncher.launch(ACCESS_FINE_LOCATION);
        }
      }

检查是否需要显示权限理性/自定义对话来教育用户

private void shouldShowRequestPermissionRationale() {
        if (!shouldShowRequestPermissionRationale(ACCESS_FINE_LOCATION)) {
          // need to show permission rational custom dialog.
        } 
    }

shouldShowRequestPermissionRationale()方法可以用来检查用户是否选择了“never asked again”选项并拒绝了权限。 有很多代码示例，所以我宁愿解释如何将它用于这样的目的，因为我认为它的名称和实现使它比实际情况更加复杂。

正如在运行时请求权限中解释的那样，如果选项“never ask again”可见，该方法返回true，否则返回false;因此，它在第一次显示对话框时返回false，然后从第二次开始返回true，只有当用户拒绝选择该选项的权限时，它才会再次返回false。

要检测这种情况，您可以检测序列false-true-false，或者(更简单)您可以使用一个标记来跟踪对话框显示的初始时间。在此之后，该方法返回true或false，其中false将允许您检测何时选择该选项。

相反，你会收到回调onRequestPermissionsResult()作为PERMISSION_DENIED当你再次请求权限时，而落在shouldShowRequestPermissionRationale()的错误条件下

来自Android文档:

When the system asks the user to grant a permission, the user has the option of telling the system not to ask for that permission again. In that case, any time an app uses requestPermissions() to ask for that permission again, the system immediately denies the request. The system calls your onRequestPermissionsResult() callback method and passes PERMISSION_DENIED, the same way it would if the user had explicitly rejected your request again. This means that when you call requestPermissions(), you cannot assume that any direct interaction with the user has taken place.

我在Android m中写了一个权限请求的简写，这段代码还处理了对旧Android版本的向后兼容性。

所有丑陋的代码都被提取到一个片段中，该片段将自己附加到请求权限的活动上。PermissionRequestManager的使用方法如下:

new PermissionRequestManager()
        // We need a AppCompatActivity here, if you are not using support libraries you will have to slightly change 
        // the PermissionReuqestManager class
        .withActivity(this)

        // List all permissions you need
        .withPermissions(android.Manifest.permission.CALL_PHONE, android.Manifest.permission.READ_CALENDAR)

        // This Runnable is called whenever the request was successfull
        .withSuccessHandler(new Runnable() {
            @Override
            public void run() {
                // Do something with your permissions!
                // This is called after the user has granted all 
                // permissions, we are one a older platform where 
                // the user does not need to grant permissions 
                // manually, or all permissions are already granted

            }
        })

        // Optional, called when the user did not grant all permissions
        .withFailureHandler(new Runnable() {
            @Override
            public void run() {
                // This is called if the user has rejected one or all of the requested permissions
                L.e(this.getClass().getSimpleName(), "Unable to request permission");

            }
        })

        // After calling this, the user is prompted to grant the rights
        .request();

来看看:https://gist.github.com/crysxd/385b57d74045a8bd67c4110c34ab74aa