Flutter中的Timer

Posted 2022-02-05 GY-93

Flutter中的Timer

• 1.单次运行的定时器
• 2. 重复运行定时器

Timer的官方文档资料

1.单次运行的定时器

• 源码：

factory Timer(Duration duration, void Function() callback) 
    if (Zone.current == Zone.root) 
      // No need to bind the callback. We know that the root's timer will
      // be invoked in the root zone.
      return Zone.current.createTimer(duration, callback);
    
    return Zone.current
        .createTimer(duration, Zone.current.bindCallbackGuarded(callback));
  

• 示例代码：

 void countDown() 
    //创建一个单次的定时器
    print("当前时间=======$DateTime.now()");
    Timer timer = Timer(const Duration(seconds: 5), ()
      print("5秒后执行定时器======$DateTime.now()");
      setState(() 
        _counter++;
      );
    );
  

如果你立刻执行一个定时器，可以调用run方法：

/// Runs the given [callback] asynchronously as soon as possible.
  ///
  /// This function is equivalent to `new Timer(Duration.zero, callback)`.
  static void run(void Function() callback) 
    new Timer(Duration.zero, callback);
  
  
static const Duration zero = Duration(seconds: 0);

• run()：方法的实质是创建一个时间为0的定时器
  创建定时器的时候， 如果传入的时间是负数或则0，这两种情况都当成时间是0，会立刻执行定时器，这一点官方文档是有说明的

2. 重复运行定时器

• 源码：

factory Timer.periodic(Duration duration, void callback(Timer timer)) 
    if (Zone.current == Zone.root) 
      // No need to bind the callback. We know that the root's timer will
      // be invoked in the root zone.
      return Zone.current.createPeriodicTimer(duration, callback);
    
    var boundCallback = Zone.current.bindUnaryCallbackGuarded<Timer>(callback);
    return Zone.current.createPeriodicTimer(duration, boundCallback);
  

• 示例代码：

void countDown2() 
    //创建一个多次重复运行的定时器
    print("当前时间=======$DateTime.now()");
    Timer timer = Timer.periodic(const Duration(seconds: 3), (timer) 
      setState(() 
        print("3秒后执行定时器======$DateTime.now()");
        _counter ++;
      );

      if (_counter == 5) 
        //循环5次之后停止定时器
        timer.cancel();
        print("执行5次之后停止定时器");
      
    );
  

• bool get isActive;判断定时器，是否处于活跃状态