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iOS子线程更新UI到主线程的三种方法

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以下代码有什么问题?如何修复?

@interface TTWaitController : UIViewController

@property (strong, nonatomic) UILabel *alert;

@end

@implementation TTWaitController

- (void)viewDidLoad
{
    CGRect frame = CGRectMake(20, 200, 200, 20);
    self.alert = [[UILabel alloc] initWithFrame:frame];
    self.alert.text = @"Please wait 10 seconds...";
    self.alert.textColor = [UIColor whiteColor];
    [self.view addSubview:self.alert];

    NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];
    [waitQueue addOperationWithBlock:^{
        [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:10]];
        self.alert.text = @"Thanks!";
    }];
}

@end

@implementation TTAppDelegate

- (BOOL)application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = [[TTWaitController alloc] init];
    [self.window makeKeyAndVisible];
    return YES;
}

这段代码是想提醒用户等待10s,10s后在标签上显示“Thanks”,但多线程代码部分NSOperationQueue的addOperationWithBlock函数不能保证block里面的语句是在主线程中运行的,UILabel显示文字属于UI更新,必须要在主线程进行,否则会有未知的操作,无法在界面上及时正常显示。

解决方法是将UI更新的代码写在主线程上即可,代码同步到主线程上主要有三种方法:NSThread、NSOperationQueue和GCD,三个层次的多线程都可以获取主线程并同步。

NSThread级主线程同步:performSelectorOnMainThread

NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];
[waitQueue addOperationWithBlock:^{
    [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:10]];
    // 同步到主线程
    [self performSelectorOnMainThread:@selector(updateUI) withObject:nil waitUntilDone:NO];
}];

/**
 * UI更新函数
 */
- (void)updateUI {
    self.alert.text = @"Thanks!";
}

NSOperationQueue级主线程同步:[NSOperationQueue mainQueue]

NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];
[waitQueue addOperationWithBlock:^{
    [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:10]];
    // 同步到主线程
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        self.alert.text = @"Thanks!";
    }];
}];

GCD级主线程同步:dispatch_get_main_queue

NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];
[waitQueue addOperationWithBlock:^{
    [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:3]];
    // 同步到主线程
    dispatch_async(dispatch_get_main_queue(), ^{
        self.alert.text = @"Thanks!";
    });
}];
作者:cordova 发表于2017/2/8 22:03:53 原文链接
阅读:15 评论:0 查看评论

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