C # differences between Action, delegate, and EventHandler,

C # differences between Action, delegate, and EventHandler,

Action is a generic delegate, which is implemented using delegate internally. When the parameters defined by a common delegate are the same as the number and type of actions, the two functions are the same. The Action method is more concise and standardized. As follows:

1 public delegate void DoDelegate (object parm); 2 public DoDelegate DoMethod; 3 4 public Action <object> doAction4OneParm; 5 public Action <object, object> doAction4TwoParm; 6 7 private void Form1_Load (object sender, EventArgs e) 8 {9 DoMethod + = DoTestMetohd; // common delegate (because a parameter is specified during the delegate definition, therefore, the method that matches a parameter) 10 doAction4OneParm + = DoTestMetohd; // Action delegate (the method that matches a parameter here) 11 doAction4TwoParm + = DoTestMetohd; // Action delegate (the method that matches two parameters here) 12} 13 14 private void DoTestMetohd (object parm) 15 {16 MessageBox. show (Convert. toString (parm); 17} 18 19 private void DoTestMetohd (object parm1, object parm2) 20 {21 MessageBox. show (Convert. toString (parm1 + "" + parm2); 22}

One of the more important differences between Action and delegate is the generics. That is, Action uses generic + delegation internally, and the number of parameters of generic methods can be expanded to 16, Microsoft. the internal code of the Action defined in. net corefx is as follows:

 1 namespace System 2 { 3     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")] 4     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9); 5  6     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")] 7     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10); 8  9     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]10     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11);11 12     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]13     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12);14 15     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]16     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13);17 18     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]19     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14);20 21     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]22     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15);23 24     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]25     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15, T16 arg16);26 }

EventHandler is an event Delegate, that is, it is also implemented internally, but it is more often defined as an event, that is, the event method.

The above is my personal opinion in use. Thank you for your correction and criticism !!!