写在前面

封装，是因为下次懒得再写！一生只爱一个。

分析

倒计时，肯定是要用到计时器了。我们会想到这个NSTimer和dispatch_source_set_timer。二者的区别点这里。

关于定时器

1、首先声明一个本地对象：

dispatch_source_t verifyTimer;//验证码定时器

2、创建一个队列，用来装载这个定时器

dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

3、创建这个定时器对象

verifyTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

4、设置定时器从现在起执行，执行的频率为每秒执行一次。

dispatch_source_set_timer(verifyTimer, dispatch_walltime(NULL, 0), 1.0*NSEC_PER_SEC, 0);//每秒执行

5、监听每次执行

__weak typeof(self)weakSelf = self;
dispatch_source_set_event_handler(verifyTimer, ^{
        if (timeout <=  0) {
            
        //倒计时结束
        dispatch_async(dispatch_get_main_queue(), ^{
             //执行一些UI上的代码

            //并释放定时器
            [weakSelf stopCountDown];
        });
}else{
       //倒计时中    
       dispatch_async(dispatch_get_main_queue(), ^{
               if (_countDownChanging) {
                    //设置按钮文字，外部返回title
                    [weakSelf setTitle:_countDownChanging(weakSelf,timeout) forState:UIControlStateNormal];
                    [weakSelf setTitle:_countDownChanging(weakSelf,timeout) forState:UIControlStateDisabled];
                }else{
                    //设置按钮文字，外部不放回，设置默认的
                    NSString *title = [NSString stringWithFormat:@"%zd秒",timeout];
                    [weakSelf setTitle:title forState:UIControlStateNormal];
                    [weakSelf setTitle:title forState:UIControlStateDisabled];
                }
                
       });
            //每次执行减1秒
            timeout--;
        }
});

6、开启定时器

dispatch_resume(verifyTimer);

7、结束定时器

dispatch_source_cancel(verifyTimer);

以上是关于整个定时器的创建、开启和结束。

全部代码

.h文件

#import <UIKit/UIKit.h>
@class WxxCountDownButton;

typedef void (^TouchedCountDownButtonHandler)(WxxCountDownButton  *countDownButton,NSInteger tag);
typedef NSString* (^CountDownChanging)(WxxCountDownButton  *countDownButton,NSUInteger second);
typedef NSString* (^CountDownFinished)(WxxCountDownButton  *countDownButton,NSUInteger second);

@interface WxxCountDownButton : UIButton

///带圆角边框的按钮
-(instancetype)initHasBorderWithNormalColor:(UIColor*)normalColor
                                changeColor:(UIColor*)changeColor;
///监听按钮事件
-(void)countButtonHandler:(TouchedCountDownButtonHandler)touchedCountDownButtonHandler;
///开始倒计时
- (void)startCountDownWithSecond:(NSUInteger)totalSecond;
///停止倒计时
- (void)stopCountDown;
///倒计时中
- (void)countDownChanging:(CountDownChanging)countDownChanging;
///倒计时结束(需要在切换页面的时候调用，以便释放定时对象)
- (void)countDownFinished:(CountDownFinished)countDownFinished;

@end

.m文件

#import "WxxCountDownButton.h"

@interface WxxCountDownButton(){
    NSInteger _second;
    NSUInteger _totalSecond;
    
    UIColor *_normalColor;
    UIColor *_changeColor;
    
    CountDownChanging _countDownChanging;
    CountDownFinished _countDownFinished;
    TouchedCountDownButtonHandler _touchedCountDownButtonHandler;
    
    dispatch_source_t verifyTimer;//定时器
    BOOL isHasBorder;//是否带边框
}

@end

@implementation WxxCountDownButton

-(instancetype)initHasBorderWithNormalColor:(UIColor*)normalColor
                                changeColor:(UIColor*)changeColor{
    self = [super init];
    if (self) {
        _normalColor = normalColor;
        _changeColor = changeColor;
        
        isHasBorder = YES;
        //边框
        self.layer.borderWidth = 1;
        self.layer.masksToBounds = YES;
        self.layer.cornerRadius = 4;
        self.layer.borderColor = normalColor.CGColor;
        //字体颜色
        [self setTitleColor:normalColor forState:UIControlStateNormal];
        [self setTitleColor:changeColor forState:UIControlStateDisabled];
    }
    return self;
}

-(void)countButtonHandler:(TouchedCountDownButtonHandler)touchedCountDownButtonHandler{
    _touchedCountDownButtonHandler = [touchedCountDownButtonHandler copy];
    [self addTarget:self action:@selector(touched:) forControlEvents:UIControlEventTouchUpInside];
}

- (void)touched:(WxxCountDownButton *)sender{
    if (_touchedCountDownButtonHandler) {
        _touchedCountDownButtonHandler(sender,sender.tag);
    }
}

#pragma -mark count down method
- (void)startCountDownWithSecond:(NSUInteger)totalSecond
{
    self.enabled = NO;
    _totalSecond = totalSecond;
    _second = totalSecond;
    
    __block NSInteger timeout = totalSecond;
    dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    verifyTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    
    dispatch_source_set_timer(verifyTimer, dispatch_walltime(NULL, 0), 1.0*NSEC_PER_SEC, 0);//每秒执行
    __weak typeof(self)weakSelf = self;
    dispatch_source_set_event_handler(verifyTimer, ^{
        if (timeout <=  0) {
            
            //倒计时结束
            dispatch_async(dispatch_get_main_queue(), ^{
//                [weakSelf setBackgroundColor:_normalColor];
                if (isHasBorder) {
                    self.layer.borderColor = _normalColor.CGColor;
                }
                [weakSelf stopCountDown];
            });
        }else{
            //倒计时中
            
            dispatch_async(dispatch_get_main_queue(), ^{
//               [weakSelf  setBackgroundColor:_changeColor];
                if (isHasBorder) {
                    self.layer.borderColor = _changeColor.CGColor;
                }
                if (_countDownChanging) {
                    [weakSelf setTitle:_countDownChanging(weakSelf,timeout) forState:UIControlStateNormal];
                    [weakSelf setTitle:_countDownChanging(weakSelf,timeout) forState:UIControlStateDisabled];
                }else{
                    NSString *title = [NSString stringWithFormat:@"%zd秒",timeout];
                    [weakSelf setTitle:title forState:UIControlStateNormal];
                    [weakSelf setTitle:title forState:UIControlStateDisabled];
                }
            });
            timeout--;
        }
    });
    dispatch_resume(verifyTimer);
}


- (void)stopCountDown{
    //停止计时线程
    if (verifyTimer) {
        dispatch_source_cancel(verifyTimer);
        verifyTimer = nil;
    }
    //按钮可用
    self.enabled = YES;
    //设置正常颜色
    if (isHasBorder) {
        self.layer.borderColor = _normalColor.CGColor;
    }
    _second = _totalSecond;
    if (_countDownFinished) {
        [self setTitle:_countDownFinished(self,_totalSecond)forState:UIControlStateNormal];
        [self setTitle:_countDownFinished(self,_totalSecond)forState:UIControlStateDisabled];
    }else{
        [self setTitle:@"重新获取" forState:UIControlStateNormal];
        [self setTitle:@"重新获取" forState:UIControlStateDisabled];
    }
}

- (void)countDownChanging:(CountDownChanging)countDownChanging{
    _countDownChanging = [countDownChanging copy];
}
- (void)countDownFinished:(CountDownFinished)countDownFinished{
    _countDownFinished = [countDownFinished copy];
}

@end

具体的按钮样式，可以自己根据需要去做修改。本demo的按钮样式是：带圆角边框，文字颜色同边框，无背景颜色

具体的使用方式如下：

 button = [[WxxCountDownButton alloc]initHasBorderWithNormalColor:[UIColor blueColor] changeColor:[UIColor lightGrayColor]];
[self.view addSubview:button];
button.frame = CGRectMake(120, 150, 80, 30);
button.titleLabel.font = [UIFont systemFontOfSize:12];
[button setTitle:@"发送验证码" forState:UIControlStateNormal];

[button countButtonHandler:^(WxxCountDownButton *countDownButton, NSInteger tag) {
    [countDownButton startCountDownWithSecond:59];
    [countDownButton countDownChanging:^NSString *(WxxCountDownButton *countDownButton, NSUInteger second) {
        NSString *title = [NSString stringWithFormat:@"(%lu)正在发送",(unsigned long)second];
        return title;
    }];
    [countDownButton countDownFinished:^NSString *(WxxCountDownButton *countDownButton, NSUInteger second) {
        return @"发送验证码";
    }];
}];

切换页面的时候，记得停止和释放：

-(void)viewWillDisappear:(BOOL)animated{
    [button stopCountDown];
}

小结

• NSTimer的话，如果是主线程的RunLoop，需要设置NSRunLoopCommonModes模式，以防止UI等操作对计时器的影响。如果是开启新的线程的话，虽然不受UI影响，但是需要手动开启RunLoop。
• 如果是dispatch_source_set_timer，计时准确，写起来也是挺方便的。
• 计时过程和计时结束对外暴露方法，可以由用户自定义显示文字，做相关UI修改。
• 自定义UIButton对外暴露的方法，用block来写，外部调用可以写到一起，简洁！