在代码块中设置UILabel文本 [英] Set UILabel text within code block

问题描述

我的NSURLConnection sendAsynchronousRequest有一个代码块，当我尝试设置UILabel的文本时，即使值存在，也永远不会设置文本。这是我的代码：

I have a code block for my NSURLConnection sendAsynchronousRequest, and when I try to set a UILabel's text, the text is never set, even though the values are there. Here's my code:

    NSString *address = [addresses objectAtIndex:indexPath.row];
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://myurl.com/%@", address]]];
    [NSURLConnection sendAsynchronousRequest:urlRequest queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        if ([data length] > 0 && error == nil)
        {
            NSString *dataOfData = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            if(![dataOfData isEqualToString:@"ERROR: address invalid"]) {
                [balanceLabel setText:[NSString stringWithFormat:@"Balance: %@", dataOfData]];
                if(data) {
                    qrCodeButton.alpha = 1;
                }
            } else {
                errorLabel.text = @"This address is invalid.";
            }
        }
        else if ([data length] == 0 && error == nil)
        {
            NSLog(@"Nothing was downloaded.");
            [balanceLabel setText:@"Server Error, Please Try Again"];
        }
        else if (error != nil){
            NSLog(@"Error = %@", error);
        }
    }];

为什么UILabel的文字从未设定？代码块有限制吗？如果是这样，我将如何解决我的问题？干杯！

Why is the UILabel's text never set? Is there a limitation to code blocks? If so, how would I fix my problem? Cheers!

推荐答案

这是因为NSOperationQueue不是主线程。你在做什么是非法的。令人遗憾的是，没有必要！只需说：

It is because an NSOperationQueue is not the main thread. What you're doing is illegal. And the sad thing is that there is no need for it! Just say:

[NSURLConnection sendAsynchronousRequest:urlRequest 
     queue:[NSOperationQueue mainQueue]
     completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        // ... and the rest exactly as you have it now

全部修复。您的请求在后台线程上是异步的，但是当它在完成处理程序上返回给您时，您将在主线程上并且能够与接口等通信。

All fixed. Your request is asynchronous on a background thread, but when it comes back to you on the completion handler, you'll be on the main thread and able to talk to the interface etc.

这篇关于在代码块中设置UILabel文本的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！