第一步，拖兩個空間textfiled和button到storyboard上的viewcontroller上。

第二步，拖線，鏈接到.h文件中代碼如下：

1	@property (weak, nonatomic) IBOutlet UIButton *l_timeButton;

第三步，在,m文件中為l_timeButton設置監聽器，監聽點擊事件。

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- (void)viewDidLoad { ????[super viewDidLoad]; ????[_l_timeButton addTarget:self action:@selector(startTime) forControlEvents:UIControlEventTouchUpInside]; }

第四步，在方法“startTime”中實現倒計時功能

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-(void)startTime{ ????__block int timeout=30; //倒計時時間 ????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); //每秒執行 ????dispatch_source_set_event_handler(_timer, ^{ ????????if(timeout<=0){ //倒計時結束，關閉 ????????????dispatch_source_cancel(_timer); ????????????dispatch_async(dispatch_get_main_queue(), ^{ ????????????????//設置界面的按鈕顯示 根據自己需求設置 ????????????????[_l_timeButton setTitle:@"發送驗證碼" forState:UIControlStateNormal]; ????????????????_l_timeButton.userInteractionEnabled = YES; ????????????}); ????????}else{ ????????????int seconds = timeout % 60; ????????????NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds]; ????????????dispatch_async(dispatch_get_main_queue(), ^{ ????????????????//設置界面的按鈕顯示 根據自己需求設置 ????????????????//NSLog(@"____%@",strTime); ????????????????[UIView beginAnimations:nil context:nil]; ????????????????[UIView setAnimationDuration:1]; ????????????????[_l_timeButton setTitle:[NSString stringWithFormat:@"%@秒后重新發送",strTime] forState:UIControlStateNormal]; ????????????????[UIView commitAnimations]; ????????????????_l_timeButton.userInteractionEnabled = NO; ????????????}); ????????????timeout--; ????????} ????}); ????dispatch_resume(_timer); }

一個驗證碼倒計時的功能就寫好了

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