XCode - 块完成时执行代码

Question

所以我试图使用ACAccountStore登录/注册用户。这发生在使用模态呈现的视图控制器上。它工作得很好，但是，当我关闭视图控制器时，底层/呈现视图控制器仍然是黑色窗口。我想这会发生，因为我不等待完成块完成。

所以我的问题：如何在致电[self dismissViewControllerAnimated:YES completion:nil];之前等待完成块完成？

-(void)loginWithTwitter{ 

ACAccountStore *account = [[ACAccountStore alloc] init]; 
ACAccountType *accountType = [account accountTypeWithAccountTypeIdentifier: 
           ACAccountTypeIdentifierTwitter]; 

[account requestAccessToAccountsWithType:accountType options:nil 
           completion:^(BOOL granted, NSError *error) 
{ 
    if (granted) { 
     //do something -> call function to handle the data and dismiss the modal controller. 
    } 
    else{ 
     //fail and put our error message. 
    } 
}]; 
} 

Answer 1

完成块是结束，将后（在此情况下帐户访问请求）来执行主处理该事情。所以你可以放入[self dismissViewControllerAnimated:YES completion:nil]。

另一件事：由于保留周期，在块中引用self是不好的。你会修改你的代码，看起来像这样：

ACAccountStore *account = [[ACAccountStore alloc] init]; 
ACAccountType *accountType = [account accountTypeWithAccountTypeIdentifier: 
     ACAccountTypeIdentifierTwitter]; 

__weak UIViewController *weakSelf = self; 
[account requestAccessToAccountsWithType:accountType options:nil 
           completion:^(BOOL granted, NSError *error) { 
    [weakSelf dismissViewControllerAnimated:YES completion:nil]; 

    if (granted) { 
     //do something -> call function to handle the data and dismiss the modal controller. 
    } 
    else { 
     //fail and put our error message. 
    } 

}];