NSTimer用法小结-阿里云开发者社区

Timers的替代方法

如果只是要延迟消息的发送，可以使用NSObject的方法

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget

创建Timer的三种方法

１.scheduling a timer with the current run loop　

２.creating a timer that you later register with a run loop

３.initializing a timer with a given fire date

Scheduled Timers

以下两个方法自动注册新创建的timer到当前NSRunLoop对象，NSRunLoop的模式为默认的NSDefaultRunLoopMode

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds invocation:(NSInvocation *)invocation repeats:(BOOL)repeats
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats

只发送一次

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 - (IBAction)startOneOffTimer:sender {   
     
     [NSTimer scheduledTimerWithTimeInterval:2.0   
              target:self   
              selector:@selector(targetMethod:)   
              userInfo:[self userInfo]   
              repeats:NO];   
 }   

重复发送消息

注：创建重复发送消息的timer一般需要保存一个引用，因为需要在某个时刻停止发送消息

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 - (IBAction)startRepeatingTimer:sender {   
     
     NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.5   
                               target:self selector:@selector(timerFireMethod:)   
                               userInfo:[self userInfo] repeats:YES];   
     self.repeatingTimer = timer;   
 }   

Unscheduled Timers

创建未注册的timer，使用时调用addTimer：forMode注册到NSRunLoop对象

timerWithTimeInterval:target:selector:userInfo:repeats:
timerWithTimeInterval:invocation:repeats:

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 - (IBAction)createUnregisteredTimer:sender {   
     
     NSMethodSignature *methodSignature = [self methodSignatureForSelector:@selector(invocationMethod:)];   
     NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];   
     [invocation setTarget:self];   
     [invocation setSelector:@selector(invocationMethod:)];   
     NSDate *startDate = [NSDate date];   
     [invocation setArgument:&startDate atIndex:2];   
     
     NSTimer *timer = [NSTimer timerWithTimeInterval:0.5 invocation:invocation repeats:YES];   
     self.unregisteredTimer = timer;   
 }   

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 - (IBAction)startUnregisteredTimer:sender {   
     if (unregisteredTimer != nil) {   
         NSRunLoop *runLoop = [NSRunLoop currentRunLoop];   
         [runLoop addTimer:unregisteredTimer forMode:NSDefaultRunLoopMode];   
     }   
 }   

Initializing a Timer with a Fire Date

创建一个拥有指定发送日期的timer

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 - (IBAction)startFireDateTimer:sender {   
     NSDate *fireDate = [NSDate dateWithTimeIntervalSinceNow:1.0];   
     NSTimer *timer = [[NSTimer alloc] initWithFireDate:fireDate   
                                       interval:0.5   
                                       target:self   
                                       selector:@selector(countedtargetMethod:)   
                                       userInfo:[self userInfo]   
                                       repeats:YES];   
     
     timerCount = 1;   
     NSRunLoop *runLoop = [NSRunLoop currentRunLoop];   
     [runLoop addTimer:timer forMode:NSDefaultRunLoopMode];   
     [timer release];   
 }   

Stopping a Timer

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 - (IBAction)stopRepeatingTimer:sender {   
     [repeatingTimer invalidate];   
     self.repeatingTimer = nil;   
 }   
     

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 也可以从timer发送的消息中停止timer   

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 - (void)countedtargetMethod:(NSTimer*)theTimer {   
     
     NSDate *startDate = [[theTimer userInfo] objectForKey:@"StartDate"];   
     NSLog(@"Timer started on %@; fire count %d", startDate, timerCount);   
     
     timerCount++;   
     if (timerCount > 3) {   
         [theTimer invalidate];   
     }   
 }   

Memory Management

1. The run loop maintains the timer that is registered to it.

2. The timer is passed as an argument when you specify its method as a selector

3. You should maintain a strong reference to the unscheduled timer, in order to ensure that it's not deallocated before you use it.

4. A timer maintains a strong reference to its user info dictionary,

5. A timer maintains a strong reference to its target, so you should make sure that your timer's target survive longer than the timer itself.