Objective-C完成区块问题

Question

我试图在异步任务中获取通讯簿的JSON (NSString *) ，但是我希望它是异步的并带有完成块。

我已经设法在没有完成块的情况下轻松地检索到了，但是当我添加完成块时，出现以下编译器错误：

不兼容的块指针类型将NSString *(^)(bool, CFErrorRef)' to parameter of type 'ABAddressBookRequestAccessCompletionHandler' (aka '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模块之内，但是我找不到适合我具体问题的良好示例/教程，如果有1个可以帮助我，我将非常高兴。

Answer 1

您的问题是您要像这样声明getAddressBook（如果我们剥离代码块）

-(id)block

您正在尝试将其作为类型的函数传递：

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

块很难与语法一起使用（迅速改进了语法），但是当我不确定时，我总是引用该站点：

块语法参考

更新：

您实际上必须等待异步方法完成。 您也可以参考官方文档

+ (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);
                                                 });
    }
}

并像这样使用它：

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