想要做一個計時器 (Timer)，可以怎麼做？使用NSTimer，每隔一秒鐘更新一次秒數，就這麼簡單！
- (void)viewDidLoad{ [super viewDidLoad]; // 設定Timer，每過1秒執行方法 self.accumulatedTime = 0; self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(updateTime:) userInfo:nil repeats:YES];}-(void)updateTime:(NSTimer *)timer{ self. accumulatedTime++; NSLog(@"accumulatedTime:%f",self. accumulatedTime);}上面是有傳Timer 為參數的寫法，如果沒有要傳 Timer 進去，就拿掉 : 即可，我正使用的中的範例：
@property (weak, nonatomic) NSTimer *checkCameraStatusTimer;//页面将要进入前台，开启定时器 -(void)viewWillAppear:(BOOL)animated { //开启定时器 self.checkCameraStatusTimer=[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(checkcamerastates) userInfo:nil repeats:YES]; [self.checkCameraStatusTimer fire]; } //页面消失，进入后台不显示该页面，关闭定时器 -(void)viewDidDisappear:(BOOL)animated { //关闭定时器 [self.checkCameraStatusTimer invalidate]; } -(void)checkcamerastates { // TODO: here.. }
Swift 範例：
[iOS] Swift how to use NSTimer background?
https://stackoverflow.max-everyday.com/2018/01/ios-swift-how-to-use-nstimer-background/