OC经验-定时器

CADisplayLink

开启定时器

self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(linkTest)];
[self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

结束定时器

[self.displayLink invalidate];

开启后定时器的调用频率跟屏幕刷新频率一样，依赖runloop不精准。

NSTimer

开启定时器

//开启1
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:proxy selector:@selector(timerTest) userInfo:nil repeats:YES];
//开启2
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        
}];
//开启3
self.timer = [NSTimer timerWithTimeInterval:1 target:self selector:@selector(timerTest) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    
//开启4
self.timer = [NSTimer timerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        
}];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];

依赖runloop不精准。

结束定时器

[self.timer invalidate];

使用scheduledTimerWithTimeInterval创建的timer会被添加到当前线程的runloop的NSDefaultRunLoopMode模式下

• CADisplayLink、NSTimer会对target产生强引用，如果target有对它们产生强引用，那么就会引发循环引用。

• 解决方法

  • 使用block 这种只能用于timer

  __weak typeof(self) weakSelf = self;
  self.timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        __strong typeof(self) strongSelf = weakSelf;
        [strongSelf timeTest];
  }];
  

  • 使用代理对象

  MyProxy2 *proxy = [MyProxy2 proxyWithTarget:self];
  self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:proxy selector:@selector(test) userInfo:nil repeats:YES];
  

  @interface MyProxy : NSObject
  +(instancetype)proxyWithTarget:(id)target;
  @property(nonatomic,weak)id target;
  @end
  
  @implementation MyProxy
  +(instancetype)proxyWithTarget:(id)target{
    MyProxy *proxy = [[MyProxy alloc] init];
    proxy.target = target;
    return proxy;
  }
  
  -(id)forwardingTargetForSelector:(SEL)aSelector{
    return self.target;
  }
  @end
  

  @interface MyProxy2 : NSProxy
  +(instancetype)proxyWithTarget:(id)target;
  @property(nonatomic,weak)id target;
  @end
  
  @implementation MyProxy2
  +(instancetype)proxyWithTarget:(id)target{
      MyProxy2 *proxy = [MyProxy2 alloc];
      proxy.target = target;
      return proxy;
  }
  
  - (nullable NSMethodSignature *)methodSignatureForSelector:(SEL)sel{
      return [self.target methodSignatureForSelector:sel];
  }
  
  - (void)forwardInvocation:(NSInvocation *)invocation{
      [invocation invokeWithTarget:self.target];
  }
  @end
  

NSProxy是专门用来做转发的类，效率更高，没有方法查找阶段，直接进入methodSignatureForSelector转发阶段。

GCD定时器

通过上面我们发现CADisplayLink、NSTimer不精准，要对计时器要求精准就得用到GCD. 开启定时器

-(void)test{
// dispatch_queue_t queue = dispatch_get_main_queue();
    //创建队列
    dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL);
    //创建计时器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    //一定要用强引用保留住timer 要不启动不了
    self.timer = timer;
    //开始时间 可以去设置
    dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, 3.0 * NSEC_PER_SEC);
    //设置开始时间，和间隔时间
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0);
    //通过block回调
// dispatch_source_set_event_handler(timer, ^{
// NSLog(@"aa");
// });
    //通过函数回调
    dispatch_source_set_event_handler_f(timer,timerFire);
    //启动定时器
    dispatch_resume(timer);
}
void timerFire(void *param){
    NSLog(@"bb，%@",[NSThread currentThread]);
}

结束定时器

dispatch_source_cancel(self.timer);