1 class Program
2 {
3 static void Main(string[] args)
4 {
5 EventDemo();
6 Console.ReadLine();
7 }
8
9 static void EventDemo()
10 {
11 MathClass mc = new MathClass();
12 mc.Age = 10;
13 mc.ChangedEvent += Mc_ChangedEvent;
14 mc.Age = 20;
15 }
16
17 private static void Mc_ChangedEvent(object sender, ChangedEventArgs e)
18 {
19 Console.WriteLine($"The old value is {e.OldValue},new value is {e.NewValue}");
20 }
21 }
22
23 interface IMath
24 {
25 void Add(int x, int y);
26
27 int Age { get; set; }
28
29 event EventHandler<ChangedEventArgs> ChangedEvent;
30 }
31
32 public class MathClass : IMath
33 {
34 private int age;
35 public int Age
36 {
37 get
38 {
39 return age;
40 }
41 set
42 {
43 if(value!=age)
44 {
45 int oldValue = age;
46 age = value;
47 int newValue = value;
48 OnChanged(oldValue, newValue);
49 }
50 }
51 }
52
53 public event EventHandler<ChangedEventArgs> ChangedEvent;
54
55 protected virtual void OnChanged(int oldValue,int newValue)
56 {
57 var handler = ChangedEvent;
58 handler?.Invoke(this, new ChangedEventArgs(oldValue, newValue));
59 }
60
61 public void Add(int x, int y)
62 {
63 Console.WriteLine($"x+y={x + y}");
64 }
65 }
66
67 public class ChangedEventArgs:EventArgs
68 {
69 public int OldValue { get; set; }
70 public int NewValue { get; set; }
71
72 public ChangedEventArgs(int oldValue,int newValue)
73 {
74 OldValue = oldValue;
75 NewValue = newValue;
76 }
77 }
