@interface UIButton (CountDown)

/**
 *
 *  倒計時按鈕
 *
 *  @param startTime 倒計時時間
 *  @param title     倒計時結束按鈕上顯示的文字
 *  @param unitTitle 倒計時的時間單位（默認為s）
 *  @param mColor    按鈕的背景色
 *  @param color     倒計時中按鈕的背景色
 */
- (void)countDownFromTime:(NSInteger)startTime title:(NSString *)title unitTitle:(NSString *)unitTitle mainColor:(UIColor *)mColor countColor:(UIColor *)color;
@end

@implementation UIButton (CountDown)
- (void)countDownFromTime:(NSInteger)startTime title:(NSString *)title unitTitle:(NSString *)unitTitle mainColor:(UIColor *)mColor countColor:(UIColor *)color {
    
    __weak typeof(self) weakSelf = self;
    
    // 剩余的時間
    __block NSInteger remainTime = startTime;
    
    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);
    // 每秒執行一次
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
    
    // 子線程（queue）執行event_handler
    dispatch_source_set_event_handler(timer, ^{
        
        if (remainTime <= 0) { // 倒計時結束
            dispatch_source_cancel(timer);
            // 主線程更新UI
            dispatch_async(dispatch_get_main_queue(), ^{
                weakSelf.backgroundColor = mColor;
                [weakSelf setTitle:title forState:UIControlStateNormal];
                weakSelf.enabled = YES;
            });
        } else {
            NSString *timeStr = [NSString stringWithFormat:@"%ld", remainTime];
            dispatch_async(dispatch_get_main_queue(), ^{
                weakSelf.backgroundColor = color;
                [weakSelf setTitle:[NSString stringWithFormat:@"%@%@",timeStr,unitTitle] forState:UIControlStateDisabled];
                weakSelf.enabled = NO;
            });
            remainTime--;
        }
    });
    dispatch_resume(timer);
}
@end