NSTimer用法

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)userInforepeats:(BOOL)repeats

 

只发送一次

- (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

- (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:

- (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;
}

- (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

- (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

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

也可以从timer发送的消息中停止timer

- (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.