ios - dispatch_async 并非一直有效

Question

我有以下代码...

-(void) SetSerialNumber
{
    NSLog(@"SetSerialNumber");
    NSString *serialNum = textFieldSecond.text;
    if (textFieldSecond.text == nil) {
        [self performSelectorOnMainThread:@selector(display:) withObject:@"Please Enter the serial number" waitUntilDone:YES];
        return;
    }

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^(void){
        NSString* response;
        [self performSelectorOnMainThread:@selector(display:) withObject:@"Sending Set  Serial Num request" waitUntilDone:YES];
        [[testApp sharedClass] SetSerNumber:serialNum];

        [self performSelectorOnMainThread:@selector(display:) withObject:@"Waiting for Response..." waitUntilDone:YES];
        response = [[Process sharedProcess] readAndProcessData:ACK];
        [self performSelectorOnMainThread:@selector(display:) withObject:rpcresponse waitUntilDone:YES];
    });
}

display: 方法将消息放到 UITextView 上。

我在按下按钮时调用此函数。有时 dispatch_async block 没有被调用。它只是通过它。但是，我每次都能看到打印的日志消息。

任何人都可以分享可能导致此问题的原因吗？

Answer 1

“落空”是什么意思？该调用是异步的，因此不会立即发生。将日志添加到 block 本身并查看它是否被打印。

您确定当它“落空”时 serialNum 不是 nil 吗？