iOS子線程更新UI到主線程的三種方法

2019-11-09 16:37:43

字體：大中小

來源：轉載

供稿：網友

以下代碼有什么問題？如何修復？

@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;}

這段代碼是想提醒用戶等待10s，10s后在標簽上顯示“Thanks”，但多線程代碼部分NSOperationQueue的addOperationWithBlock函數不能保證block里面的語句是在主線程中運行的，UILabel顯示文字屬于UI更新，必須要在主線程進行，否則會有未知的操作，無法在界面上及時正常顯示。

解決方法是將UI更新的代碼寫在主線程上即可，代碼同步到主線程上主要有三種方法：NSThread、NSOperationQueue和GCD，三個層次的多線程都可以獲取主線程并同步。

NSThread級主線程同步：performSelectorOnMainThread

NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];[waitQueue addOperationWithBlock:^{ [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:10]]; // 同步到主線程 [self performSelectorOnMainThread:@selector(updateUI) withObject:nil waitUntilDone:NO];}];/** * UI更新函數 */- (void)updateUI { self.alert.text = @"Thanks!";}

NSOperationQueue級主線程同步：[NSOperationQueue mainQueue]

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

GCD級主線程同步：dispatch_get_main_queue

NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];[waitQueue addOperationWithBlock:^{ [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:3]]; // 同步到主線程 dispatch_async(dispatch_get_main_queue(), ^{ self.alert.text = @"Thanks!"; });}];

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