PerformSelecter

當調(diào)用 NSObject 的 performSelecter:afterDelay: 后包归，實際上其內(nèi)部會創(chuàng)建一個 Timer 并添加到當前線程的 RunLoop 中回怜。所以如果當前線程沒有 RunLoop翘紊，則這個方法會失效。

當調(diào)用 performSelector:onThread: 時暮刃，實際上其會創(chuàng)建一個 Timer 加到對應的線程去跨算，同樣的，如果對應線程沒有 RunLoop 該方法也會失效椭懊。

其他的performSelector系列方法是類似的

直接上代碼

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self tryPerformSelectorOnMianThread];
    
    __weak typeof(self) weakSelf = self;
    //backGroundThread并不會被調(diào)用到,這是因為诸蚕，在調(diào)用performSelector:onThread: withObject: waitUntilDone的時候，系統(tǒng)會給我們創(chuàng)建一個Timer的source氧猬，加到對應的RunLoop上去背犯，然而這個時候我們沒有RunLoop
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [weakSelf tryPerformSelectorOnbackGroundThread1];
    });
    
    //在tryPerformSelectorOnbackGroundThread1上我們添加個RunLoop,此時backGroundThread2就可以被調(diào)用到
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [weakSelf tryPerformSelectorOnbackGroundThread2];
    });
    
    //那么為什么主線程中的perfom selector卻能夠正常調(diào)用呢？通過上面的例子相信你已經(jīng)猜到了盅抚，主線程的RunLoop是一直存在的漠魏，所以我們在主線程中執(zhí)行的時候，無需再添加RunLoop妄均。
    //小結(jié):當perform selector在后臺線程中執(zhí)行的時候柱锹，這個線程必須有一個開啟的runLoop
}

- (void)tryPerformSelectorOnMianThread{
    [self performSelector:@selector(mainThreadMethod) withObject:nil];
}

- (void)tryPerformSelectorOnbackGroundThread1{
    //backGroundThread并不會被調(diào)用到,這是因為哪自，在調(diào)用performSelector:onThread: withObject: waitUntilDone的時候，系統(tǒng)會給我們創(chuàng)建一個Timer的source禁熏，加到對應的RunLoop上去壤巷，然而這個時候我們沒有RunLoop
    [self performSelector:@selector(backGroundThread1) onThread:[NSThread currentThread] withObject:nil waitUntilDone:NO];
    //默認是會在MainRunLoop中去執(zhí)行,故他可以調(diào)用到backGroundThread
//    [self performSelector:@selector(backGroundThread1) withObject:nil];
    [self tryPerformSelectorOnbackGroundThread2];
}

- (void)tryPerformSelectorOnbackGroundThread2{
    //在tryPerformSelectorOnbackGroundThread1上我們添加個RunLoop,此時backGroundThread2就可以被調(diào)用到
    [self performSelector:@selector(backGroundThread2) onThread:[NSThread currentThread] withObject:nil waitUntilDone:NO];
    [[NSRunLoop currentRunLoop] run];
}

- (void)mainThreadMethod{
    NSLog(@"execute %s",__func__);
}

- (void)backGroundThread1{
    NSLog(@"currentThread:%@",[NSThread currentThread]);
    NSLog(@"backGroundThread1 --> execute %s",__FUNCTION__);
}

- (void)backGroundThread2{
    NSLog(@"currentThread:%@",[NSThread currentThread]);
    NSLog(@"backGroundThread2 --> execute %s",__FUNCTION__);
}