检查当前线程是否是主线程

Question

有没有办法检查当前线程是否是Objective-C中的主线程？

我想做这样的事情.

  - (void)someMethod
  {
    if (IS_THIS_MAIN_THREAD?) {
      NSLog(@"ok. this is main thread.");
    } else {
      NSLog(@"don't call this method from other thread!");
    }
  }

Answer 1

看看NSThreadAPI文档.

有像这样的方法

- (BOOL)isMainThread

+ (BOOL)isMainThread

和 + (NSThread *)mainThread

Answer 2

如果要在主线程上执行方法,可以:

- (void)someMethod
{
    dispatch_block_t block = ^{
        // Code for the method goes here
    };

    if ([NSThread isMainThread])
    {
        block();
    }
    else
    {
        dispatch_async(dispatch_get_main_queue(), block);
    }
}

Answer 3

在Swift3中

if Thread.isMainThread {
    print("Main Thread")
}

Answer 4

如果你想知道你是否在主线程上,你可以简单地使用调试器.在您感兴趣的行设置断点,当程序到达时,请调用:

(lldb) thread info

这将显示有关您所在线程的信息:

(lldb) thread info thread #1: tid = 0xe8ad0, 0x00000001083515a0 MyApp`MyApp.ViewController.sliderMoved (sender=0x00007fd221486340, self=0x00007fd22161c1a0)(ObjectiveC.UISlider) -> () + 112 at ViewController.swift:20, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1

如果是的值queue是com.apple.main-thread,那么你在主线程上.

Answer 5

以下模式将确保在主线程上执行方法:

- (void)yourMethod {
    // make sure this runs on the main thread 
    if (![NSThread isMainThread]) {
        [self performSelectorOnMainThread:_cmd/*@selector(yourMethod)*/
                               withObject:nil
                            waitUntilDone:YES];
        return;
    }
    // put your code for yourMethod here
}