6.15 Creating Timers

定时器，循环执行某一任务

看下书上的例子

- (void) paint:(NSTimer *)paramTimer{

    /* Do something here */

    NSLog(@"Painting");

}

- (void) startPainting{

    self.paintingTimer = [NSTimer scheduledTimerWithTimeInterval:1.0

                                                          target:self

                                                        selector:@selector(paint:)

                                                        userInfo:nil

                                                         repeats:YES];

}

- (void) stopPainting{

    if (self.paintingTimer != nil){

        [self.paintingTimer invalidate];

    }

}

- (void)applicationWillResignActive:(UIApplication *)application

{

    [self stopPainting];

}

- (void)applicationDidBecomeActive:(UIApplication *)application

{

    [self startPainting];

}

输出：

2014-03-12 16:30:58.362 cookbook[710:a0b] Painting

2014-03-12 16:30:59.362 cookbook[710:a0b] Painting

2014-03-12 16:31:00.362 cookbook[710:a0b] Painting

2014-03-12 16:31:01.362 cookbook[710:a0b] Painting

。。。。。。

[self.paintingTimer invalidate]; invalidate方法会释放掉定时器，不需要再手动释放。它不仅会释放定时器本身，还会释放它retain的 userInfo参数对象。

如果repeats值是NO。则定时器在触发后会自己invalidate

还可以用NSInvocation来创建定时器

- (void) startPainting{

    /* Here is the selector that we want to call */

    SEL selectorToCall = @selector(paint:);

    /* Here we compose a method signature out of the selector.

     We know that the selector is in the current class so it is easy to construct the method signature */

    NSMethodSignature *methodSignature =[[self class] instanceMethodSignatureForSelector:selectorToCall];

    /* Now base the invocation on the method signature. We need this invocation to schedule a timer */

    NSInvocation *invocation =[NSInvocation invocationWithMethodSignature:methodSignature];

    [invocation setTarget:self];

    [invocation setSelector:selectorToCall];

    /* Start a scheduled timer now */

    self.paintingTimer = [NSTimer scheduledTimerWithTimeInterval:1.0

                                                      invocation:invocation

                                                         repeats:YES];

}

还可以先创建，需要的时候在手动加到Run loop里面去

- (void) startPainting{

    self.paintingTimer = [NSTimer timerWithTimeInterval:1.0 target:self

                                               selector:@selector(paint:)

                                               userInfo:nil

                                                repeats:YES];

    /* Do your processing here and, whenever you are ready,

     use the addTimer:forMode instance method of the NSRunLoop class in order to schedule the timer on that run loop */

    [[NSRunLoop currentRunLoop] addTimer:self.paintingTimer forMode:NSDefaultRunLoopMode];

}

   

当然了，也可以NSInvocation加手动

- (void) startPainting{

    /* Here is the selector that we want to call */

    SEL selectorToCall = @selector(paint:);

    /* Here we compose a method signature out of the selector. We

     know that the selector is in the current class so it is easy

     to construct the method signature */

    NSMethodSignature *methodSignature =[[self class] instanceMethodSignatureForSelector:selectorToCall];

    /* Now base the invocation on the method signature. We need this invocation to schedule a timer */

    NSInvocation *invocation =[NSInvocation invocationWithMethodSignature:methodSignature];

    [invocation setTarget:self];

    [invocation setSelector:selectorToCall];

    self.paintingTimer = [NSTimer timerWithTimeInterval:1.0

                                             invocation:invocation

                                                repeats:YES];;

    /* Do your processing here and, whenever you are ready,

     use the addTimer:forMode instance method of the NSRunLoop class in order to schedule the timer on that run loop */

    [[NSRunLoop currentRunLoop] addTimer:self.paintingTimer forMode:NSDefaultRunLoopMode];

}