iOS: 常驻线程

如何开启

首先开启一个线程：

@property (nonatomic, strong) NSThread *thread;

- (IBAction)startAction:(id)sender {
    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(start) object:nil];
    thread.name = @"com.live.thread";
    // 开启子线程
    [thread start];
    self.thread = thread;
}

- (void)start {
    NSLog(@"start----%@",[NSThread currentThread]);
}

- (IBAction)taskAction:(id)sender {
    /*
     如果设置wait为YES:等待当前线程执行完以后，主线程才会执行aSelector方法；
     设置为NO：不等待当前线程执行完，就在主线程上执行aSelector方法。
     如果，当前线程就是主线程，那么aSelector方法会马上执行。
     */
    [self performSelector:@selector(task) onThread:self.thread withObject:nil waitUntilDone:YES];
    
}

- (void)task {
    NSLog(@"task----%@",[NSThread currentThread]);
}

根据代码可知，执行startAction，打印

start----<NSThread: 0x280b84c40>{number = 6, name = com.live.thread}

我们知道一个线程执行完任务后就会自动销毁，再次调用此线程去执行任务即会报错：

所以我们一般启动Runloop来使线程常驻，修改代码如下：

- (void)start {
    NSLog(@"start----%@",[NSThread currentThread]);
    @autoreleasepool {
        do {
            [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
        } while (YES);
    }
}

便可成功执行task：

start----<NSThread: 0x2807d5300>{number = 7, name = com.live.thread}

task----<NSThread: 0x2807d5300>{number = 7, name = com.live.thread}

如何停止

代码如下：

@property (nonatomic, assign) BOOL cancelled;

- (IBAction)stopAction:(id)sender {
    [self performSelector:@selector(stop) onThread:self.thread withObject:nil waitUntilDone:NO];

    NSLog(@"退出runLoop");
}

- (void)start {
    NSLog(@"start----%@",[NSThread currentThread]);
    @autoreleasepool {
        do {
            [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
        } while (!self.cancelled);
    }
}

- (void)stop {
    self.cancelled = YES;
}

添加一个flag操控，执行stopAction后，再次操作task便又会报错，说明Runloop停止了