Question

我正在使用Timer在相当长的间隔（2分钟）内定期运行事件。这工作正常。但是我希望在创建计时器时立即触发事件（而不是等待2分钟）。

请注意，我不能仅通过调用该方法来执行此操作，因为它需要一些时间来运行并会阻止应用程序。我需要正常启动计时器并在单独的线程中运行事件。

我现在想到这样做的最好方法是对计时器进行子类化并创建一个TriggerManually方法来做类似这样的事情：

关闭自动重置
将间隔设置为1毫秒
启用计时器

这会立即触发已发生的事件，我可以将所有设置恢复正常。

虽然看起来有点迂回。有没有更好的方法呢？

Answer 1

你不能手动调用已发生事件的事件处理程序吗？

即使您希望它在线程池线程上执行，也可以调用它。

class Blah
{
    private Timer mTimer;

    public Blah()
    {
        mTimer = new Timer(120000);

        ElapsedEventHandler handler = new ElapsedEventHandler(Timer_Elapsed);
        mTimer.Elapsed += handler;
        mTimer.Enabled = true;

        //Manually execute the event handler on a threadpool thread.
        handler.BeginInvoke(this, null, new AsyncCallback(Timer_ElapsedCallback), handler);
    }

    private static void Timer_Elapsed(object source, ElapsedEventArgs e)
    {
        //Do stuff...
    }

    private void Timer_ElapsedCallback(IAsyncResult result)
    {
        ElapsedEventHandler handler = result.AsyncState as ElapsedEventHandler;
        if (handler != null)
        {
            handler.EndInvoke(result);
        }
    }
}

Answer 2

您可以使用System.Threading.Timer吗？它有一个构造函数，允许您选择间隔和延迟（可以设置为0立即开始）。 http://msdn.microsoft.com/en-us/library/2x96zfy7.aspx

Answer 3

我喜欢Rob Cooke的答案，因此我构建了一个小EagerTimer类，其子类System.Timers.Timer并添加了此功能。（来自these articles）

的提示

我知道我可以使用System.Threading.Timer代替，但这很简单，在我的应用程序中效果很好。

<强> EagerTimer

/// <summary>
// EagerTimer is a simple wrapper around System.Timers.Timer that
// provides "set up and immediately execute" functionality by adding a
// new AutoStart property, and also provides the ability to manually
// raise the Elapsed event with RaiseElapsed.
/// </summary>
public class EagerTimer : Timer
{
    public EagerTimer()
        : base() { }

    public EagerTimer(double interval)
        : base(interval) { }

    // Need to hide this so we can use Elapsed.Invoke below
    // (otherwise the compiler complains)
    private event ElapsedEventHandler _elapsedHandler;
    public new event ElapsedEventHandler Elapsed
    {
        add { _elapsedHandler += value; base.Elapsed += value; }
        remove { _elapsedHandler -= value; base.Elapsed -= value; }
    }

    public new void Start()
    {
        // If AutoStart is enabled, we need to invoke the timer event manually
        if (AutoStart)
        {
            this._elapsedHandler.BeginInvoke(this, null, new AsyncCallback(AutoStartCallback), _elapsedHandler); // fire immediately
        }

        // Proceed as normal
        base.Start();
    }

    private void AutoStartCallback(IAsyncResult result)
    {
        ElapsedEventHandler handler = result.AsyncState as ElapsedEventHandler;
        if (handler != null) handler.EndInvoke(result);
    }

    // Summary:
    //     Gets or sets a value indicating whether the EagerTimer should raise
    //     the System.Timers.Timer.Elapsed event immediately when Start() is called,
    //     or only after the first time it elapses. If AutoStart is false, EagerTimer behaves
    //     identically to System.Timers.Timer.
    //
    // Returns:
    //     true if the EagerTimer should raise the System.Timers.Timer.Elapsed
    //     event immediately when Start() is called; false if it should raise the System.Timers.Timer.Elapsed
    //     event only after the first time the interval elapses. The default is true.
    [Category("Behavior")]
    [DefaultValue(true)]
    [TimersDescription("TimerAutoStart")]
    public bool AutoStart { get; set; }

    /// <summary>
    /// Manually raises the Elapsed event of the System.Timers.Timer.
    /// </summary>
    public void RaiseElapsed()
    {
        if (_elapsedHandler != null)
            _elapsedHandler(this, null);
    }
}

单元测试

[TestClass]
public class Objects_EagerTimer_Tests
{
    private const int TimerInterval = 10; // ms

    private List<DateTime> _timerFires = new List<DateTime>();
    private DateTime _testStart;

    [TestInitialize]
    public void TestSetup()
    {
        _timerFires.Clear();
        _testStart = DateTime.Now;
    }

    [TestMethod]
    public void Objects_EagerTimer_WithAutoStartDisabled()
    {
        // EagerTimer should behave as a normal System.Timers.Timer object
        var timer = new EagerTimer(TimerInterval);
        timer.AutoReset = false;
        timer.Elapsed += timerElapsed;
        timer.Start();

        // Wait (not enough time for first interval)
        Thread.Sleep(5);
        Assert.IsFalse(_timerFires.Any());

        // Wait a little longer
        Thread.Sleep(TimerInterval);
        Assert.AreEqual(1, _timerFires.Count);
    }

    [TestMethod]
    public void Objects_EagerTimer_WithAutoStartEnabled()
    {
        // EagerTimer should fire immediately on Start()
        var timer = new EagerTimer(TimerInterval);
        timer.AutoReset = false;
        timer.AutoStart = true;
        timer.Elapsed += timerElapsed;
        timer.Start();

        // Wait (not enough time for first interval)
        Thread.Sleep(5);
        Assert.IsTrue(_timerFires.Any());

        // Wait a little longer, now it will have fired twice
        Thread.Sleep(TimerInterval);
        Assert.AreEqual(2, _timerFires.Count);
    }

    [TestMethod]
    public void Objects_EagerTimer_WhenRaisingManually()
    {
        // EagerTimer should fire immediately on Start()
        var timer = new EagerTimer(TimerInterval);
        timer.AutoReset = false;
        timer.AutoStart = false;
        timer.Elapsed += timerElapsed;

        Assert.IsFalse(_timerFires.Any());
        timer.RaiseElapsed();
        Assert.IsTrue(_timerFires.Any());
    }

    private void timerElapsed(object sender, ElapsedEventArgs e) {
        _timerFires.Add(DateTime.Now);
    }
}

立即激活.net System.Timers.Timer

3 个答案: