Apple development of iOS verification code countdown

The first step, drag two space textfiled and button to the storyboard on the Viewcontroller.

The second step, drag the line, link to the. h file in the following code:

@property (Weak, nonatomic) Iboutlet UIButton *l_timebutton;

In the third step, set the listener for L_timebutton in the M file and listen for the Click event.

-(void) Viewdidload {
[Super Viewdidload];
[_l_timebutton addtarget:self Action: @selector (StartTime) forcontrolevents:uicontroleventtouchupinside];
}

The fourth step, in the method "StartTime" to achieve the countdown function

-(void) starttime{
__block int timeout=30; Countdown time
dispatch_queue_t queue = Dispatch_get_global_queue (Dispatch_queue_priority_default, 0);
dispatch_source_t _timer = dispatch_source_create (dispatch_source_type_timer, 0, 0,queue);
Dispatch_source_set_timer (_timer,dispatch_walltime (NULL, 0), 1.0*nsec_per_sec, 0); Execute per second
Dispatch_source_set_event_handler (_timer, ^{
if (timeout<=0) {//countdown ended, off
Dispatch_source_cancel (_timer);
Dispatch_async (Dispatch_get_main_queue (), ^{
Set the button of the interface to display according to your own needs
[_l_timebutton settitle:@ "Send authentication Code" Forstate:uicontrolstatenormal];
_l_timebutton.userinteractionenabled = YES;
});
}else{
int seconds = timeout% 60;
NSString *strtime = [NSString stringwithformat:@ "%.2d", seconds];
Dispatch_async (Dispatch_get_main_queue (), ^{
Set the button of the interface to display according to your own needs
NSLog (@ "____%@", strtime);
[UIView Beginanimations:nil Context:nil];
[UIView Setanimationduration:1];
[_l_timebutton settitle:[nsstring stringwithformat:@ "%@ seconds later Resend", Strtime] forstate:uicontrolstatenormal];
[UIView commitanimations];
_l_timebutton.userinteractionenabled = NO;
});
timeout--;
}
});
Dispatch_resume (_timer);
}
Well, a verification code countdown function is written. Also, another method, later when I study well, in the introduction to everyone. Attach the running picture as follows: