NSTimer 用法小结

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
1 - (IBAction)startTimer:sender {  
2    
3     [NSTimer scheduledTimerWithTimeInterval:2.0  
4              target:self  
5              selector:@selector(targetMethod:)  
6              userInfo:[self userInfo]  
7              repeats:NO];  //需要重复调用目标方法时，repeats设置为YES
8 }

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　　[timer　invalidate];

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:
 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 }  
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

 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

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

也可以从timer发送的消息中停止timer 

 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.
posted @ 2013-03-26 21:47  ubersexual  阅读(488)  评论(0)  编辑  收藏  举报