Event 事件

当一个事件注册多个 Handler 时，事件的触发顺序是不确定的。这取决于编译器的实现，以及 Handler 的执行时间。

public class Program
{
    public static void Main()
    {
        var eventExample = new EventExample();
        eventExample.MyEvent += EventExample_FirstHandler;
        eventExample.MyEvent += EventExample_SecondHandler;
        eventExample.MyEvent += EventExample_ThirdHandler;
        eventExample.RaiseEvent();
    }

    private static void EventExample_FirstHandler(object sender, EventArgs e)
    {
        Console.WriteLine($"First handler called, {DateTime.Now}");
    }

    private static void EventExample_SecondHandler(object sender, EventArgs e)
    {
        Console.WriteLine($"Second handler called, {DateTime.Now}");
        Thread.Sleep(5000);
    }

    private static void EventExample_ThirdHandler(object sender, EventArgs e)
    {
        Console.WriteLine($"Third handler called, {DateTime.Now}");
    }
}

public class EventExample
{
    public event EventHandler MyEvent;

    public void RaiseEvent()
    {
        MyEvent?.Invoke(this, EventArgs.Empty);
    }
}

// Output
// First handler called, 2023/4/23 13:44:10
// Second handler called, 2023/4/23 13:44:10
// Third handler called, 2023/4/23 13:44:15