IOS scrollView添加Timer后不响应scrollViewWillBeginDragging事件，这是为什么啊？

Question

添加Timer代码

- (void) createTimer
{
    NSTimer *timer = [NSTimer timerWithTimeInterval:3.0 target:self selector:@selector(increaseCurrentPage) userInfo:nil repeats:YES];
    self.timer = timer;
    //消息循环
    NSRunLoop *runloop = [NSRunLoop currentRunLoop];
    [runloop addTimer:timer forMode:NSDefaultRunLoopMode];}

[self createTimer]在viewDidLoad中调用，当不注释掉[self createTimer]的时候，

- (void) scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    [self.timer invalidate];
    NSLog(@"draggged");
}

这段代码没有响应，不响应断点，只有当[self createTimer]注释掉之后，才会响应，这是为什么呢

Answer 1

 [runloop addTimer:timer forMode:NSDefaultRunLoopMode];

Changed to:

 [runloop addTimer:timer forMode:NSRunLoopCommonModes];

Try it!

Answer 2

I would like to ask【NSTImer sch. . . 】What is the difference from init?