6.18 Exiting Threads and Timers

停止线程，停止定时器

NSThread *thread = /* Get the reference to your thread here */; 

[thread cancel];

NSTimer *timer = /* Get the reference to your timer here */; 

[timer invalidate];

请注意在退出线程时不要用exit，因为用exit的话，线程没机会清理现场，会造成内存泄露。

不过，我还真不知道如何来调用exit，因为他是类方法，一调用就报错：No visible @interface for 'NSThread' declares the selector 'exit'

看个例子

- (void) threadEntryPoint{

    @autoreleasepool {

        NSLog(@"Thread Entry Point");

        while ([[NSThread currentThread] isCancelled] == NO){

            [NSThread sleepForTimeInterval:4];

//            if ([[NSThread currentThread] isCancelled] == NO){

                NSLog(@"Thread Loop");

//            }

        }

        NSLog(@"Thread Finished");

    }

}

- (void) stopThread{

    NSLog(@"Cancelling the Thread");

    [self.myThread cancel];

    NSLog(@"Releasing the thread");

    self.myThread = nil;

}

-(void)test6_18

{

    self.myThread = [[NSThread alloc] initWithTarget:self

                                            selector:@selector(threadEntryPoint)

                                              object:nil];

    [self performSelector:@selector(stopThread)

               withObject:nil

               afterDelay:6.0f];

    [self.myThread start];

}

输出：

2014-03-13 15:57:32.305 cookbook[811:360b] Thread Entry Point

2014-03-13 15:57:36.307 cookbook[811:360b] Thread Loop

2014-03-13 15:57:38.306 cookbook[811:a0b] Cancelling the Thread

2014-03-13 15:57:38.308 cookbook[811:a0b] Releasing the thread

2014-03-13 15:57:40.309 cookbook[811:360b] Thread Loop

2014-03-13 15:57:40.310 cookbook[811:360b] Thread Finished

从打印的结果可以看出，虽然线程cancel了，但是它在睡醒之后却仍然执行了一次。比较好的做法是在睡醒之后再去判断下线程是否取消了，然后在执行，如上被注释掉得那部分。