iphone - 我想在 block 执行后返回值

Question

- (NSString *) BBB {
    __block NSString *returnValue;

    NSDictionary *queryParameters = @{ @"q" : @"SELECT uid FROM user WHERE uid = me()"};
    [FBRequestConnection startWithGraphPath:@"fql" parameters:queryParameters HTTPMethod:@"GET" completionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
        returnValue = result[@"data"][0][@"uid"];
        NSLog(@"inside block -> %@", returnValue);
    }];

    return returnValue;
}

我想返回正确的值，但 FBRequestConnection 是一个异步请求。returnValue 的 make 值为 (null)，因为它在执行 FBRequestConnection 的 completionBlock 之前返回。

Answer 1

如果您需要将该值返回给特定方法，一个简单的解决方案可能是将依赖该值的代码移至其他方法。您也可以考虑设置一个等待指示器。在这种情况下，用户将知道正在运行一个操作。

- (void)BBB {    

    __weak SelfType weakSelf = self; // to prevent possible memory leaks if you use ARC

    NSDictionary *queryParameters = @{ @"q" : @"SELECT uid FROM user WHERE uid = me()"};
    [FBRequestConnection startWithGraphPath:@"fql" parameters:queryParameters HTTPMethod:@"GET" completionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
        returnValue = result[@"data"][0][@"uid"];
        NSLog(@"inside block -> %@", returnValue);

        __strong SelfType safeSelf = weakSelf;
        if(safeSelf) {
            // notify that the operation is finished
            [safeSelf DDDWithReturnValue:returnValue];
        }
    }];
}

我提供的代码在 ARC 下工作。如果您的代码未启用 ARC，请使用

__block SelfType weakSelf = self; // for non-ARC code