iOS子线程更新UI到主线程的三种方法

2019-11-09 15:22:11

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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!"; });}];

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