最近工作比较忙，然后最近也在尝试着翻译一篇关于CALayer非常详解的一篇文章，文章还是比较好也比较长的，等整理完了再发布出来吧。所以也没啥多余的时间写些东西，就先来分享一下开发中的一些小Tips吧。

一、倒计时问题
在开发中经常遇到倒计时倒计时问题，写一个Button，然后各种判断各种状态，好多代码感觉很乱，下面就分享一下，一句话解决倒计时问题的例子（当然不是万能的，只适合大部分普通的倒计时^_）！
先看效果
https://img.haomeiwen.com/i571495/92c1547f64ea24f6.gif?imageMogr2/auto-orient/strip

再看看我们的代码
<pre>
//
// ViewController.m
// HWCountdownDemo
//
// Created by HenryCheng on 16/1/4.
// Copyright © 2016年 www.igancao.com. All rights reserved.
//

import "ViewController.h"

import "UIButton+countDown.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIButton *countdownBtn;

@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];

}

• (IBAction)countdownBtnClick:(UIButton *)sender {
  [_countdownBtn startWithTime:5 title:@"获取验证码" countDownTitle:@"s" mainColor:[UIColor colorWithRed:84/255.0 green:180/255.0 blue:98/255.0 alpha:1.0f] countColor:[UIColor lightGrayColor]];
  }

• (void)didReceiveMemoryWarning {
  [super didReceiveMemoryWarning];
  // Dispose of any resources that can be recreated.
  }

@end
</pre>
这里主要的就是xib拉了一个button然后连接了它的属性和方法，我们可以看到就调用了
<pre>[_countdownBtn startWithTime:5 title:@"获取验证码" countDownTitle:@"s" mainColor:[UIColor colorWithRed:84/255.0 green:180/255.0 blue:98/255.0 alpha:1.0f] countColor:[UIColor lightGrayColor]];}</pre>

这一句代码，就完成了倒计时功能。
这里我写了一个category，里面代码是这样的
<pre>
//
// UIButton+countDown.m
// LiquoriceDoctorProject
//
// Created by HenryCheng on 15/12/4.
// Copyright © 2015年 iMac. All rights reserved.
//

import "UIButton+countDown.h"

@implementation UIButton (countDown)

• (void)startWithTime:(NSInteger)timeLine title:(NSString *)title countDownTitle:(NSString *)subTitle mainColor:(UIColor *)mColor countColor:(UIColor *)color {

  //倒计时时间
  __block NSInteger timeOut = timeLine;
  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);
  //每秒执行一次
  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 (timeOut <= 0) {
        dispatch_source_cancel(_timer);
        dispatch_async(dispatch_get_main_queue(), ^{
            self.backgroundColor = mColor;
            [self setTitle:title forState:UIControlStateNormal];
            self.userInteractionEnabled = YES;
        });
    } else {
        int seconds = timeOut % 60;
        NSString *timeStr = [NSString stringWithFormat:@"%0.2d", seconds];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.backgroundColor = color;
            [self setTitle:[NSString stringWithFormat:@"%@%@",timeStr,subTitle] forState:UIControlStateNormal];
            self.userInteractionEnabled = NO;
        });
        timeOut--;
    }
  

  });
  dispatch_resume(_timer);
  }

@end
</pre>
关于这个方法的定义
<pre>
//
// UIButton+countDown.h
// LiquoriceDoctorProject
//
// Created by HenryCheng on 15/12/4.
// Copyright © 2015年 iMac. All rights reserved.
//

import <UIKit/UIKit.h>

@interface UIButton (countDown)

/**

• 倒计时按钮
• @param timeLine 倒计时总时间
• @param title 还没倒计时的title
• @param subTitle 倒计时中的子名字，如时、分
• @param mColor 还没倒计时的颜色
• @param color 倒计时中的颜色
  */

• (void)startWithTime:(NSInteger)timeLine title:(NSString *)title countDownTitle:(NSString *)subTitle mainColor:(UIColor *)mColor countColor:(UIColor *)color;

@end
</pre>