NSTimer 用法总结

1、初始化

+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;

注：不用scheduled方式初始化的，需要手动addTimer:forMode: 将timer添加到一个runloop中。

　　而scheduled的初始化方法将以默认mode直接添加到当前的runloop中.

举例：

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:@selector(timerFired:) userInfo:nil repeats:NO];

或

NSTimer *myTimer = [NSTimertimerWithTimeInterval:3.0 target:selfselector:@selector(timerFired:) userInfo:nilrepeats:NO];

[[NSRunLoopcurrentRunLoop] addTimer:myTimerforMode:NSDefaultRunLoopMode];

 

2、触发（启动）

当定时器创建完（不用scheduled的，添加到runloop中后，该定时器将在初始化时指定的timeInterval秒后自动触发。

可以使用-(void)fire;方法来立即触发该定时器；

注：You can use this method to fire a repeating timer without interrupting its regular firing schedule. If the timer is non-repeating, it is automatically invalidated after firing, even if its scheduled fire date has not arrived.

在重复执行的定时器中调用此方法后立即触发该定时器，但不会中断其之前的执行计划；

在不重复执行的定时器中调用此方法，立即触发后，就会使这个定时器失效。

 

3、停止

- (void)invalidate;

这个是唯一一个可以将计时器从runloop中移出的方法。

 

注：

NSTimer可以精确到50-100毫秒.

NSTimer不是绝对准确的,而且中间耗时或阻塞错过下一个点,那么下一个点就pass过去了.

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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1. - (IBAction)startOneOffTimer:sender {  
2.    
3.     [NSTimer scheduledTimerWithTimeInterval:2.0  
4.              target:self  
5.              selector:@selector(targetMethod:)  
6.              userInfo:[self userInfo]  
7.              repeats:NO];  
8. }  

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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1. - (IBAction)startRepeatingTimer:sender {  
2.    
3.     NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.5  
4.                               target:self selector:@selector(timerFireMethod:)  
5.                               userInfo:[self userInfo] repeats:YES];  
6.     self.repeatingTimer = timer;  
7. }  

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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1. - (IBAction)createUnregisteredTimer:sender {  
2.    
3.     NSMethodSignature *methodSignature = [self methodSignatureForSelector:@selector(invocationMethod:)];  
4.     NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];  
5.     [invocation setTarget:self];  
6.     [invocation setSelector:@selector(invocationMethod:)];  
7.     NSDate *startDate = [NSDate date];  
8.     [invocation setArgument:&startDate atIndex:2];  
9.    
10.     NSTimer *timer = [NSTimer timerWithTimeInterval:0.5 invocation:invocation repeats:YES];  
11.     self.unregisteredTimer = timer;  
12. }  

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1. - (IBAction)startUnregisteredTimer:sender {  
2.     if (unregisteredTimer != nil) {  
3.         NSRunLoop *runLoop = [NSRunLoop currentRunLoop];  
4.         [runLoop addTimer:unregisteredTimer forMode:NSDefaultRunLoopMode];  
5.     }  
6. }  

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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1. - (IBAction)startFireDateTimer:sender {  
2.     NSDate *fireDate = [NSDate dateWithTimeIntervalSinceNow:1.0];  
3.     NSTimer *timer = [[NSTimer alloc] initWithFireDate:fireDate  
4.                                       interval:0.5  
5.                                       target:self  
6.                                       selector:@selector(countedtargetMethod:)  
7.                                       userInfo:[self userInfo]  
8.                                       repeats:YES];  
9.    
10.     timerCount = 1;  
11.     NSRunLoop *runLoop = [NSRunLoop currentRunLoop];  
12.     [runLoop addTimer:timer forMode:NSDefaultRunLoopMode];  
13.     [timer release];  
14. }  

Stopping a Timer

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1. - (IBAction)stopRepeatingTimer:sender {  
2.     [repeatingTimer invalidate];  
3.     self.repeatingTimer = nil;  
4. }  
5.    

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1. 也可以从timer发送的消息中停止timer  

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1. - (void)countedtargetMethod:(NSTimer*)theTimer {  
2.    
3.     NSDate *startDate = [[theTimer userInfo] objectForKey:@"StartDate"];  
4.     NSLog(@"Timer started on %@; fire count %d", startDate, timerCount);  
5.    
6.     timerCount++;  
7.     if (timerCount > 3) {  
8.         [theTimer invalidate];  
9.     }  
10. }  

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.