系統默認注冊了5個Mode:
kCFRunLoopDefaultMode：App的默認Mode，通常主線程是在這個Mode下運行

UITrackingRunLoopMode：界面跟蹤 Mode，用于 ScrollView 追蹤觸摸滑動，保證界面滑動時不受其他 Mode 影響

UIInitializationRunLoopMode: 在剛啟動 App 時第進入的第一個 Mode，啟動完成后就不再使用

GSEventReceiveRunLoopMode: 接受系統事件的內部 Mode，通常用不到

kCFRunLoopCommonModes: 這是一個占位用的Mode，不是一種真正的Mode

CFRunLoopModeRef代表RunLoop的運行模式
一個 RunLoop 包含若干個 Mode，每個Mode又包含若干個Source/Timer/Observer

每次RunLoop啟動時，只能指定其中一個 Mode，這個Mode被稱作 CurrentMode

如果需要切換Mode，只能退出Loop，再重新指定一個Mode進入

這樣做主要是為了分隔開不同組的Source/Timer/Observer，讓其互不影響

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
//         定時器可以運行
        NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(run) userInfo:nil repeats:YES];
        
        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
    });
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//         定時器無法運行
        NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(run) userInfo:nil repeats:YES];
        
        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
    });
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(run) userInfo:nil repeats:YES];
//         定時器無法運行
        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
    });
    
    dispatch_async(dispatch_get_main_queue(), ^{
        NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(run) userInfo:nil repeats:YES];
//         定時器可以運行
        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
        
    });
    

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.thread = [[HJThread alloc] initWithTarget:self selector:@selector(invoke) object:nil];
    [self.thread start];
}

- (void)invoke
{
　　@autoreleasepool{
    NSLog(@"******invoke*****%@", [NSThread currentThread]);
　　　// 添加一個port讓runloop可以運行循環
    [[NSRunLoop currentRunLoop] addPort:[NSPort port] forMode:NSDefaultRunLoopMode];
    [[NSRunLoop currentRunLoop] run];
　　}
    NSLog(@"************");
}

- (void)touchInvoke
{
    NSLog(@"*********touchInvoke*********%@", [NSThread currentThread]);
    
    NSLog(@"%@", [NSRunLoop currentRunLoop]);
}

// 屏幕點擊
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self performSelector:@selector(touchInvoke) onThread:self.thread withObject:nil waitUntilDone:NO];
}

#import "ViewController.h"

@interface ViewController () <NSURLConnectionDataDelegate>
/** runLoop */
@property (nonatomic, assign) CFRunLoopRef runLoop;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 如果在子線程中使用NSURLConnection發送請求是不會有效果,因為子線程的runloop沒有啟動,子線程runloop默認是不啟動的
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSURLConnection *conn = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.baidu.com/images/234234324limgAB/2342lkjasdf3kkkkk.jpg"]] delegate:self];
        // 決定代理方法在哪個隊列中執行
        [conn setDelegateQueue:[[NSOperationQueue alloc] init]];
        
        // 啟動子線程的runLoop
//        [[NSRunLoop currentRunLoop] run];
        
        // 保存當前runloop
        self.runLoop = CFRunLoopGetCurrent();
        
        // 啟動runLoop
        CFRunLoopRun();
    });
}

#pragma mark - <NSURLConnectionDataDelegate>
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSLog(@"didReceiveResponse******%@", [NSThread currentThread]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    
    NSLog(@"didReceiveData******%@", [NSThread currentThread]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"connectionDidFinishLoading******%@", [NSThread currentThread]);
    
    // 停止RunLoop
    CFRunLoopStop(self.runLoop);
}

@end

//     任務自動調度,無需手動fire
    [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(run) userInfo:nil repeats:YES];
    
    ------------------2種方式等價------------------
    
//    任務自動調度,無需手動fire
    NSTimer *timer = [NSTimer timerWithTimeInterval:3 target:self selector:@selector(run) userInfo:nil repeats:YES];
    //         定時器可以運行
    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];

typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
    kCFRunLoopEntry = (1UL << 0),        // : 即將到 runloop
    kCFRunLoopBeforeTimers = (1UL << 1), // : 即將處理 timer 之前
    kCFRunLoopBeforeSources = (1UL << 2),// : 即將處理 source 之前
    kCFRunLoopBeforeWaiting = (1UL << 5),// : 即將休眠
    kCFRunLoopAfterWaiting = (1UL << 6), // : 休眠之后
    kCFRunLoopExit = (1UL << 7),         // : 退出
    kCFRunLoopAllActivities = 0x0FFFFFFFU// : 所有的活動
};

- (IBAction)btnClick:(id)sender {
    NSLog(@"btnDidClick*****");
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
　　// 監聽runloop狀態變化
    [self observer];
}

- (void)observer
{
    // 創建observer
    CFRunLoopObserverRef observer = CFRunLoopObserverCreateWithHandler(CFAllocatorGetDefault(), kCFRunLoopAllActivities, YES, 0, ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
        NSLog(@"****監聽到RunLoop狀態發生改變**%zd", activity);
    });

    // 添加觀察者：監聽RunLoop的狀態
    CFRunLoopAddObserver(CFRunLoopGetCurrent(), observer, kCFRunLoopDefaultMode);
    
    // 釋放Observer
    CFRelease(observer);
}