触发事件，检查是否注册过事件的方法下面的代码，会发现事件没有被注册
class PRogram { static void Main(string[] args) { EventCheck check = new EventCheck(); check.OnDataArrived(new DataArrivedEventArgs() { data="Hello World!"}); Console.ReadKey(); } static void check_DataArrived(object sender, DataArrivedEventArgs e) { Console.WriteLine(e.data); } } class EventCheck { //第三步 use the delegate type to declare a variable that can refer to any method with the same signature as the delegate. //To associate the event with the method that will handle the event, add an instance of the delegate to the event. //The event handler is called whenever the event occurs, unless you remove the delegate. internal event DataArrivedEventHandler DataArrived; //第四步 internal void OnDataArrived(DataArrivedEventArgs e) { try { //DataArrivedEventHandler handler = DataArrived; //if (handler != null) //{ // handler(this, e); //} DataArrived += EventCheck_DataArrived; if (DataArrived != null) { DataArrived -= EventCheck_DataArrived; DataArrived(this, e); } } catch (Exception ex) { Console.WriteLine("遇到异常{0}", ex.Message); } } void EventCheck_DataArrived(object sender, DataArrivedEventArgs e) { Console.WriteLine(e.data); } } //第二步 Represents the method that will handle an event when the event provides data. //This method's first parameter is of type Object and refers to the instance that raises the event. //Its second parameter is derived from type EventArgs and holds the event data. //If the event does not generate event data, the second parameter is simply the value of the EventArgs.Empty field. //Otherwise, the second parameter is a type derived from EventArgs and supplies any fields or properties needed to hold the event data. delegate void DataArrivedEventHandler(object sender,DataArrivedEventArgs e); //正式写代码的时候，可以使用EventHandler<TEventArgs>泛型委托 //第一步 //create a custom event data class, create a class that derives from the EventArgs class and provide the properties to store the necessary data. //The name of your custom event data class should end with EventArgs. class DataArrivedEventArgs : EventArgs { internal string data; }
修改第四步的代码，先将事件复制到临时变量里面，然后通过这个临时变量来处理，就不会有问题
//第四步 internal void OnDataArrived(DataArrivedEventArgs e) { try { //DataArrivedEventHandler handler = DataArrived; //if (handler != null) //{ // handler(this, e); //} DataArrived += EventCheck_DataArrived; DataArrivedEventHandler handler = DataArrived; if (handler != null) { DataArrived -= EventCheck_DataArrived; handler(this, e); } } catch (Exception ex) { Console.WriteLine("遇到异常{0}", ex.Message); } }