iOS开发 Block内部如何实现弹框等待输入结果

[daniel_xing]

- (void)doSomethingWithBlock:(NSString *(^)())block {
    NSLog(@"callback:%@", block());
}
- (void)callMethod {
    
    __weak typeof(self) weakSelf = self;
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_semaphore_t sema = dispatch_semaphore_create(0);
    
    dispatch_async(queue, ^{
        [self doSomethingWithBlock:^NSString *{
            __block NSString *resultString = nil;
            __strong typeof(weakSelf) strongSelf = weakSelf;
            // 信号量
            
            UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"message..." preferredStyle:UIAlertControllerStyleAlert];
            
            [alertController addTextFieldWithConfigurationHandler:nil];
            [alertController addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil]];
            [alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                // 获取弹框输入值
                resultString = [[alertController.textFields objectAtIndex:0] text];
            }]];
            
            [strongSelf presentViewController:alertController animated:YES completion:^{
                // 完成信号
                dispatch_semaphore_signal(sema);
            }];
            // 等待
            dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
            return resultString;
        }];
    });
}

这段代码感觉上是没有问题的~ 但是触发callMethod就立即会弹出弹框并输出callback:(null)，无奈不知道如何解决，求大神

[daniel_xing]

我自己已经得到答案，信号量放错了地方，应该放在点击OK的响应下