如何从 objective c 中的块中 return 布尔值？

Question

大家好，在用户选择允许或不允许访问照片库的选项后，尝试对我从块中调用的方法 return 一个布尔值。我怎样才能 return 来自这个特定块的布尔值？

(BOOL)checkIfUserHasAccessToPhotosLibrary{
    PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];
   
        if (status == PHAuthorizationStatusNotDetermined) {

        NSLog(@"Access has not been determined check again");
            __block BOOL boolean=false;
        [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
            
             if (status == PHAuthorizationStatusAuthorized) {
               
                 NSLog(@"User responded has access to photos library");
                 boolean=true;
  
             }

             else {
                 
                 NSLog(@"User responded does has access to photos library");
                 boolean=false;
                 
             }

         }];
    }

}

Answer 1

您问的是：

How to return boolean from a block in objective c?

你没有。

您在方法中使用了完成处理程序块参数，可能像这样：

- (void)checkPhotosLibraryAccessWithCompletion:(void (^ _Nonnull)(BOOL))completion {
    PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];

    if (status == PHAuthorizationStatusNotDetermined) {
        [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
            completion(status == PHAuthorizationStatusAuthorized);
        }];
    } else {
        completion(status == PHAuthorizationStatusAuthorized);
    }
}

然后你会像这样使用它：

[self checkPhotosLibraryAccessWithCompletion:^(BOOL success) {
    // use success here

    if (success) {
        ...
    } else {
        ...
    }
}];

// but not here, because the above runs asynchronously (i.e. later)

如何从 objective c 中的块中 return 布尔值？

How to return boolean from a block in objective c?

objective-c

ios