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 = [NSTimer timerWithTimeInterval:3.0 target:selfselector:@selector(timerFired:)userInfo:nilrepeats:NO];
[[NSRunLoop currentRunLoop] 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.
延时函数和Timer的使用
//延时函数： [NSThread sleepForTimeInterval:5.0]； //暂停5s. //Timer的使用： NSTimer *connectionTimer; //timer对象 //实例化timer self.connectionTimer=[NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(timerFired:) userInfo:nil repeats:NO];[[NSRunLoop currentRunLoop]addTimer:self.connectionTimer forMode:NSDefaultRunLoopMode]; //用timer作为延时的一种方法 do{[[NSRunLoopcurrentRunLoop]runUntilDate:[NSDatedateWithTimeIntervalSinceNow:1.0]];}while(!done); //timer调用函数 -(void)timerFired:(NSTimer *)timer{done =YES;}
转自：http://magicalboy.com/objective_c_nstimer_usage/#comment-45
创建 NSTimer
- Scheduled Timers & Using Selector
- ( IBAction ) startOneOffTimer: sender {
[ NSTimer scheduledTimerWithTimeInterval: 2.0
target: self
selector: @selector ( targetMethod: )
userInfo: [ self userInfo ]
repeats: NO ];
}
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如上，如果没有重复执行的timer相当于
[self performSelector:@selector(targetMethod:) withObject:nil afterDelay:2.0];
// declcare
@property ( assign ) NSTimer * repeatingTimer ;
// implements
- ( IBAction ) startRepeatingTimer: sender {
NSTimer * timer = [ NSTimer scheduledTimerWithTimeInterval: 0.5
target: self selector: @selector ( timerFireMethod: )
userInfo: [ self userInfo ] repeats: YES ];
self . repeatingTimer = timer ;
}
- ( IBAction ) stopRepeatingTimer: sender {
[ repeatingTimer invalidate ];
self . repeatingTimer = nil ;
}
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- Unscheduled Timers & Using Invocation
// declare
@property (retain) NSTimer *unregisteredTimer;
// implements
- (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];
}
}
- (IBAction)stopUnregisteredTimer:sender {
[unregisteredTimer invalidate];
self.unregisteredTimer = nil;
}
