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
- scheduling a timer with the current run loop
- creating a timer that you later register with a run loop
- 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
- The run loop maintains the timer that is registered to it.
- The timer is passed as an argument when you specify its method as a selector
- You should maintain a strong reference to the unscheduled timer, in order to ensure that it's not deallocated before you use it.
- A timer maintains a strong reference to its user info dictionary,
- 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.