iOS 使用 GCD 实现按钮的倒计时效果

在用户注册页面时，大部分需要用户输入手机号并获取验证码，而常见的处理方式是，点击了获取验证码按钮后，按钮会显示倒计时数字并且不可点击，当倒计时结束后按钮可以再次点击并再次获取验证码。接下来使用 GCD 实现这个小需求。

当用户点击获取验证码按钮后，调用以下方法

#pragma mark -- 开启倒计时效果
-(void)openCountdown{
    
    // 倒计时时间
    __block NSInteger time = 59;
    
    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);
    // 每秒执行
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0);
    
    dispatch_source_set_event_handler(_timer, ^{
        
        // 倒计时结束，关闭
        if(time <= 0){
            
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                
                // 设置按钮的样式
                self.YanzhengmaBtn.titleLabel.font = [UIFont systemFontOfSize:13];
                [self.YanzhengmaBtn setTitle:@"重新发送" forState:UIControlStateNormal];
                [self.YanzhengmaBtn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
                self.YanzhengmaBtn.backgroundColor = RGB(81, 183, 200);
                self.YanzhengmaBtn.userInteractionEnabled = YES;
            });
            
        }else{
            
            int seconds = time % 60;
            dispatch_async(dispatch_get_main_queue(), ^{
                
                // 设置按钮显示读秒效果
                self.YanzhengmaBtn.titleLabel.font = [UIFont systemFontOfSize:12];
                [self.YanzhengmaBtn setTitle:[NSString stringWithFormat:@"重新发送(%.2d)", seconds] forState:UIControlStateNormal];
                [self.YanzhengmaBtn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
                self.YanzhengmaBtn.backgroundColor = RGB(200, 200, 200);
                self.YanzhengmaBtn.userInteractionEnabled = NO;
            });
            time--;
        }
    });
    dispatch_resume(_timer);
}

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