自定义计时器，通过dispatch_after()实现

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1、设计思路

1.1、系统类NSTimer做一次性计时使用还可以，如果需要暂停继续的话就不太灵活了；
1.2、通过dispatch_after延时执行函数，配套循环语句算法实现间隔n秒触发一次调用；
1.3、设计一个状态属性，对当前的状态进行管理，如准备、暂停、继续、开始、结束等；

2、相关属性与方法

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//
//  SATimer.h
//  Test
//
//  Created by 余西安 on 16/8/11.
//  Copyright ? 2016年 Sian. All rights reserved.
//
 
#import <foundation /Foundation.h>
// 定时器状态
typedef NS_ENUM(NSInteger, SATimerStatus){
    SATimerStatusReady = 0, // 准备
    SATimerStatusRunning,   // 正在运行
    SATimerStatusPaused,    // 已暂停，可继续计时
    SATimerStatusStoped     // 已停止，只能重新开始
};
 
typedef void (^SATimerBlock)(NSUInteger remainCount);
 
@interface SATimer : NSObject
// 间隔时间
@property (nonatomic, assign) NSTimeInterval interval;
// 重复次数
@property (nonatomic, assign) NSUInteger     repeatCount;
 
@property (nonatomic, assign) SATimerStatus  status;
 
+ (instancetype)timeWithInterval:(NSTimeInterval)ti repeatCount:(NSInteger)count block:(SATimerBlock)block;
 
- (instancetype)initWithInterval:(NSTimeInterval)ti repeatCount:(NSInteger)count block:(SATimerBlock)block;
// 开始（重新开始）
- (void)start;
// 暂停（可继续）
- (void)pause;
// 继续
- (void)continues;
// 停止（不可继续，只能重新开始）
- (void)stop;
 
@end
</foundation>

3、实现

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//
//  SATimer.m
//  Test
//
//  Created by 余西安 on 16/8/11.
//  Copyright ? 2016年 Sian. All rights reserved.
//
 
#import "SATimer.h"
 
@interface SATimer ()
 
@property (nonatomic, assign) NSInteger  currentCount;
 
@property (nonatomic, copy) SATimerBlock block;
 
@end
 
@implementation SATimer
 
+ (instancetype)timeWithInterval:(NSTimeInterval)ti repeatCount:(NSInteger)count block:(SATimerBlock)block
{
    return [[self alloc] initWithInterval:ti repeatCount:count block:block];
}
 
- (instancetype)initWithInterval:(NSTimeInterval)ti repeatCount:(NSInteger)count block:(SATimerBlock)block
{
    if (self = [super init]){
        self.interval = ti;
        self.repeatCount = count;
        self.currentCount = count;
        self.block = block;
    }
    return self;
}
 
- (void)repeatMethod
{
 
    if (self.currentCount <= 0 || self.status != SATimerStatusRunning) return;
    self.currentCount--;
    if (self.block) self.block(self.currentCount);
 
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (self.interval * NSEC_PER_SEC));
    dispatch_after(time, dispatch_get_main_queue(), ^{
 
 
        [self repeatMethod];
    });
 
}
 
- (void)start
{
    if (self.status == SATimerStatusRunning) return;
    self.currentCount = self.repeatCount;
    self.status = SATimerStatusRunning;
    [self repeatMethod];
}
 
- (void)continues
{
    if (self.status == SATimerStatusRunning || self.currentCount == 0) return;
    self.status = SATimerStatusRunning;
    [self repeatMethod];
}
 
- (void)pause
{
    self.status = SATimerStatusPaused;
}
 
- (void)stop
{
    self.status = SATimerStatusStoped;
    self.currentCount = 0;
}
 
- (void)setCurrentCount:(NSInteger)currentCount
{
    self->_currentCount = currentCount;
    if (currentCount == 0) self.status = SATimerStatusStoped;
}
 
- (void)dealloc
{
    NSLog(@"%@---dealloc", self);
}
 
@end

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