iOS: 常驻线程

Posted 2020-12-11 walsh

如何开启

首先开启一个线程：

 1 @property (nonatomic, strong) NSThread *thread;
 2 
 3 - (IBAction)startAction:(id)sender {
 4     NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(start) object:nil];
 5     thread.name = @"com.live.thread";
 6     // 开启子线程
 7     [thread start];
 8     self.thread = thread;
 9 }
10 
11 - (void)start {
12     NSLog(@"start----%@",[NSThread currentThread]);
13 }
14 
15 - (IBAction)taskAction:(id)sender {
16     /*
17      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；
18      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。
19      如果，当前线程就是主线程，那么aSelector方法会马上执行。
20      */
21     [self performSelector:@selector(task) onThread:self.thread withObject:nil waitUntilDone:YES];
22     
23 }
24 
25 - (void)task {
26     NSLog(@"task----%@",[NSThread currentThread]);
27 }

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：

1 - (void)start {
2     NSLog(@"start----%@",[NSThread currentThread]);
3     @autoreleasepool {
4         do {
5             [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
6         } while (YES);
7     }
8 }

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：

 1 @property (nonatomic, assign) BOOL cancelled;
 2 
 3 - (IBAction)stopAction:(id)sender {
 4     [self performSelector:@selector(stop) onThread:self.thread withObject:nil waitUntilDone:NO];
 5 
 6     NSLog(@"退出runLoop");
 7 }
 8 
 9 - (void)start {
10     NSLog(@"start----%@",[NSThread currentThread]);
11     @autoreleasepool {
12         do {
13             [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
14         } while (!self.cancelled);
15     }
16 }
17 
18 - (void)stop {
19     self.cancelled = YES;
20 }

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