iphone - 更新主线程上的标签不起作用

Question

我正在尝试在不同的任务进行时更新标签。我搜索并使用了不同的选项并最终使用这种方式，但它仍然不起作用:

[processStatusLable performSelectorOnMainThread:@selector(setText:) withObject:@"Creating your account..." waitUntilDone:NO];
DCConnector *dccon = [DCConnector new];
ContactsConnector *conCon = [ContactsConnector new];

if (![dccon existUsersData]) {
    [dccon saveUsersInformation:device :usDTO];
    //created account

    //get friends -> Server call
    [processStatusLable performSelectorOnMainThread:@selector(setText:) withObject:@"Checking for friends..." waitUntilDone:NO];
    NSMutableArray *array = [conCon getAllContactsOnPhone];
    // save friends
    [processStatusLable performSelectorOnMainThread:@selector(setText:) withObject:@"Saving friends.." waitUntilDone:NO];
    if ([dccon saveContacts:array]) {
        [processStatusLable performSelectorOnMainThread:@selector(setText:) withObject:@"Friends saved successfully.." waitUntilDone:NO];
    }
}

最后一个 performSelector 正在执行(至少我看到 View 上的标签文本发生了变化)，但所有其他选择器都不起作用。知道为什么吗？

编辑 1

- (void)updateLabelText:(NSString *)newText {
    processStatusLable.text = newText;
}

Answer 1

我们可以使用下面的代码在主线程上运行一些东西，

dispatch_async(dispatch_get_main_queue(), ^{
  //set text label
});

使用它我们可以编写这样的方法，

- (void)updateLabelText:(NSString *)newText {    
    dispatch_async(dispatch_get_main_queue(), ^{
       processStatusLable.text = newText;
    });   
}

最后，您可以使用这种方式更改您的代码，

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    [self updateLabelText:@"Creating your account..."];
    DCConnector *dccon = [DCConnector new];
    ContactsConnector *conCon = [ContactsConnector new];

    if (![dccon existUsersData]) {
        [dccon saveUsersInformation:device :usDTO];
        //created account

        //get friends -> Server call
        [self updateLabelText:@"Checking for friends..."];
        NSMutableArray *array = [conCon getAllContactsOnPhone];
        // save friends
        [self updateLabelText:@"Saving friends.."];
        if ([dccon saveContacts:array]) {
        [self updateLabelText:@"Friends saved successfully.."];
        }
    }
});