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我正在尝试学习使用dispatch_get_global_queue异步执行网络调用。基本上，我需要根据用户的位置更新用户界面。我开始使用dispatch_get_global_queue是因为在执行网络呼叫时用户界面没有响应。

现在，我的问题是调用 buttonUpdate 时按钮显示不正确。一个按钮应该是黑色的，另一个是绿色的。但是，现在它们都显示为默认的蓝色。此外，在我单击其中一个之前，不会出现按钮的单词/标题。有谁知道为什么？谢谢！

我preButtonUpdate调用了这个方法，它异步调用 buttonUpdate 方法：

-(void)preButtonUpdate { 
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{
            [self buttonUpdate];
        });   
    }

在 viewDidAppear 和 appReturnsActive 中调用 preButtonUpdate 方法：

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [self preButtonUpdate];
    //other code
}

- (void)appReturnsActive {

    [myTimer invalidate];
    myTimer = nil;

    //ONLY WANT TO PERFORM THE UPDATE IF VIEWING THE PROFILE VIEW CONTROLLER
    UIViewController *currentVC = self.navigationController.visibleViewController;
    NSString * name = NSStringFromClass([currentVC class]);
    if ([name isEqualToString:@"ProfileViewController"]) { 

        [self preButtonUpdate];    
    }
}

然后，preButtonUpdate 调用 buttonUpdate 方法，该方法执行 Web 查询并更新用户界面：

-(void) buttonUpdate {
    [locationManagerProfile stopUpdatingLocation];
    NSString *userLatitude =[(PDCAppDelegate *)[UIApplication sharedApplication].delegate 
    getUserLatitude];
    NSString *userLongitude =[(PDCAppDelegate *)[UIApplication sharedApplication].delegate 
    getUserLongitude];

    NSString *placeLatitude = [[NSUserDefaults standardUserDefaults]
    stringForKey:@"savedLatitude"];

    NSString *placeLongitude = [[NSUserDefaults standardUserDefaults]
    stringForKey:@"savedLongitude"];

    NSString *distanceURL = [NSString stringWithFormat:@"http://www.website.com/page.php?
    lat1=%@&lon1=%@&lat2=%@&lon2=%@",userLatitude, userLongitude, placeLatitude, 
    placeLongitude];

    NSData *distanceURLResult = [NSData dataWithContentsOfURL:[NSURL 
    URLWithString:distanceURL]];

    NSString *distanceInFeet = [[NSString alloc] initWithData:distanceURLResult 
    encoding:NSUTF8StringEncoding];

    if ([distanceInFeet isEqualToString:@"1"]) {

        UIBarButtonItem *btnGo = [[UIBarButtonItem alloc] initWithTitle:@"Button A" 
        style:UIBarButtonItemStyleBordered target:self action:@selector(actionA)];
        self.navigationItem.rightBarButtonItem = btnGo;
        [self.navigationItem.rightBarButtonItem setTintColor:[UIColor 
        colorWithRed:44.0/255.0 green:160.0/255.0 blue:65.0/255.0 alpha:1.0]];  
        UIBarButtonItem *btnGoTwo = [[UIBarButtonItem alloc] initWithTitle:@"Button B" 
        style:UIBarButtonItemStyleBordered target:self action:@selector(actionB)];
        self.navigationItem.rightBarButtonItem = btnGoTwo; 
        self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:btnGo, 
        btnGoTwo, nil];
    }
    if ([distanceInFeet isEqualToString:@"0"]) {
        UIBarButtonItem *btnGo = [[UIBarButtonItem alloc] initWithTitle:@"Button C" 
        style:UIBarButtonItemStyleBordered target:self action:@selector(actionC)];
        self.navigationItem.rightBarButtonItem = btnGo;
        [self.navigationItem.rightBarButtonItem setTintColor:[UIColor 
        colorWithRed:44.0/255.0 green:160.0/255.0 blue:65.0/255.0 alpha:1.0]];        
        UIBarButtonItem *btnGoTwo = [[UIBarButtonItem alloc] initWithTitle:@"Button B" 
        style:UIBarButtonItemStyleBordered target:self action:@selector(actionB)];
        self.navigationItem.rightBarButtonItem = btnGoTwo;   
        self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:btnGo, 
        btnGoTwo, nil];
    }       
}
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1 回答 1

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UI Update总是在主线程上完成。所以不要让你的 UI 更新代码despatch queue

远离街区[self buttonUpdate];_dispatch_async

-(void)preButtonUpdate { 
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{
            [self buttonUpdate];
        });   
    }

解锁您的用户界面 - Apple Developer

编辑：

将 if 条件代码放在dispatch_async块外

于 2013-06-24T08:12:48.830 回答