ios - objective-c 完成 block 问题

Question

我试图在异步任务中获取地址簿的 JSON (NSString *)，但我希望它是异步的并带有一个完成 block 。

我已经设法在没有完成 block 的情况下轻松检索，但是当我添加完成 block 时出现以下编译器错误:

不兼容的 block 指针类型将 NSString *(^)(bool, CFErrorRef)' 传递给 'ABAddressBookRequestAccessCompletionHandler' 类型的参数(又名 'void (^)(bool, CFErrorRef)')

这是我的代码

+ (NSString *) getAddressBook:(id (^)())block {
ABAuthorizationStatus status = ABAddressBookGetAuthorizationStatus();

if (status == kABAuthorizationStatusDenied)
{
    // if you got here, user had previously denied/revoked permission for your
    // app to access the contacts, and all you can do is handle this gracefully,
    // perhaps telling the user that they have to go to settings to grant access
    // to contacts
    [[[UIAlertView alloc] initWithTitle:nil message:@"This app requires access to your contacts to function properly. Please visit to the \"Privacy\" section in the iPhone Settings app." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
    return nil;
}
CFErrorRef error = NULL;
ABAddressBookRef addressBook = ABAddressBookCreateWithOptions(NULL, &error);

if (error)
{
    NSLog(@"ABAddressBookCreateWithOptions error: %@", CFBridgingRelease(error));
    if (addressBook) CFRelease(addressBook);
    return nil;
}

if (status == kABAuthorizationStatusNotDetermined)
{
    // present the user the UI that requests permission to contacts ...
    ABAddressBookRequestAccessWithCompletion(addressBook, ^(bool granted, CFErrorRef error) -> THE ERROR OCCURS HERE !
                                             {...

我认为问题出在我的完成 block 中，但我找不到针对我的特定问题的一些好的示例/教程，如果有人能帮助我，我会非常高兴。

Answer 1

你的问题是你像这样声明 getAddressBook(如果我们剥离 block )

-(id)block

并且您正在尝试将其作为类型函数传递:

-(void)block:(BOOL)aBool error:(CFErrorRef*)error

block 很难与语法一起使用(这在 swift 中得到了改进)但是我总是在不确定时引用这个网站:

block syntax reference

更新:

您实际上必须等待您的异步方法完成。您也可以引用official documentation

+ (void) getAddressBook:((^)(NSString* result))block {
    ABAuthorizationStatus status = ABAddressBookGetAuthorizationStatus();

    if (status == kABAuthorizationStatusDenied)
    {
        // if you got here, user had previously denied/revoked permission for your
        // app to access the contacts, and all you can do is handle this gracefully,
        // perhaps telling the user that they have to go to settings to grant access
        // to contacts
        [[[UIAlertView alloc] initWithTitle:nil message:@"This app requires access to your contacts to function properly. Please visit to the \"Privacy\" section in the iPhone Settings app." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
        block(nil);
    }
    CFErrorRef error = NULL;
    ABAddressBookRef addressBook = ABAddressBookCreateWithOptions(NULL, &error);

    if (error)
    {
        NSLog(@"ABAddressBookCreateWithOptions error: %@", CFBridgingRelease(error));
        if (addressBook) CFRelease(addressBook);
        block(nil);
    }

    if (status == kABAuthorizationStatusNotDetermined)
    {


        // present the user the UI that requests permission to contacts ...
        ABAddressBookRequestAccessWithCompletion(addressBook, ^(bool granted, CFErrorRef error) -> THE ERROR OCCURS HERE !
                                                 {
                                                     NSString* result = whatever

                                                     block(result);
                                                 });
    }
}

然后像这样使用它:

[YourClass getAddressBook:^(NSString* result)
 {
     //now you really have result
 }];