draggingStartedBlock didn't work when UIView dragged fast enough

In Demo, FPViewController.m , I use draggingStartedBlock

``` objc
- (IBAction)actionSwitch:(UISwitch*)sender {
[self.draggableViews enumerateObjectsUsingBlock:^(UIView* obj, NSUInteger idx, BOOL *stop) {
[obj setDraggable:sender.isOn];
obj.draggingStartedBlock= ^(){
NSLog(@"dragging!~!~!~!");
};
}];
}
```

when I drag UIView slowly, it works well, but when I drag UIView fast enough, draggingStartedBlock doesn't work.

I think the problem is , when `- (void)handlePan:(UIPanGestureRecognizer*)sender` is called, `sender.state` is alreay 'UIGestureRecognizerStateChanged' .
I'm not sure and I wonder whether there are some good solutions.

THANK YOU.