使iOS块同步执行 [英] Make iOS blocks execute synchronously

问题描述

如何使块同步执行，或使函数在返回语句之前等待处理程序，因此可以从块中传回数据？

How can I make a block execute synchronously, or make the function wait for the handler before the return statement, so the data can be passed back from the block?

-(id)performRequest:(id)args
{
__block NSData *data = nil;   

    [xyzclass requestAccessToAccountsWithType:accountType withCompletionHandler:^(BOOL granted, NSError *error) {
        data = [NSData dataWithData:responseData];
    }];

    return data;
}

推荐答案

-(id)performRequest:(id)args
{
    __block NSData *data = nil;   
     dispatch_semaphore_t sem = dispatch_semaphore_create(0);
     [xyzclass requestAccessToAccountsWithType:accountType withCompletionHandler:^(BOOL granted, NSError *error) {
       data = [NSData dataWithData:responseData];
       dispatch_semaphore_signal(sem);
     }];
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
    return data;
}

信号量将阻止执行进一步的语句，直到接收到信号，你的函数不会过早返回。

semaphore will block execution of further statements until signal is received, this will make sure that your function does not return prematurely.

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