方法一：

-(void) viewDidLoad{
[self performSelectorInBackground:@selector(call1) withObject:nil]; 
}

-(void) call1{
timer1 = [NSTimer scheduledTimerWithTimeInterval:3.0 target:self selector:@selector(doSomething) userInfo:nil repeats:NO];

[[NSRunLoop currentRunLoop] addTimer:timer1 forMode:NSRunLoopCommonModes];

}

-(void) call2{
// do something
timer1 invalidate];
timer1 = nil;
}

方法二：

-(void)viewDidAppear:(BOOL)animated {
    NSThread* timerThread =[[NSThread alloc] initWithTarget:self selector:@selector(timerStart)object:nil];
    [timerThread start];}-(void)timerStart
{
    NSAutoreleasePool*pool =[[NSAutoreleasePool alloc] init];
    NSRunLoop* runLoop =[NSRunLoop currentRunLoop];
    timer =[[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(method) userInfo:nil repeats:YES] retain];//一定要retain，不然timerStart执行完后，NSTimer就被释放了。
    [runLoop run];
    [pool release];}-(void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [timer invalidate];}

方法三：

timer = [NSTimer timerWithTimeInterval:5.0 target:self selector:@selector(SendHeartBeat) userInfo:nil repeats:YES];

 [[NSRunLoop mainRunLoop] addTimer:heartTimer forMode:NSDefaultRunLoopMode];