1 private void textBox3_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
 2 {
 3     //阻止从键盘输入键
 4     e.Handled = true;
 5     if(e.KeyChar>='0' && e.KeyChar <='9')
 6     {
 7         e.Handled = false;
 8     }
 9 
10 }
11 或者
12 private void tbID_KeyPress(object sender, KeyPressEventArgs e)
13         {
14             if (!((e.KeyChar >= '0' && e.KeyChar <= '9') || e.KeyChar == ' '))//不输入输入除了数字之外的所有非法字符的判断
15             {
16                 e.Handled = true;
17             }
18         }
19 
20 
21 多条件的：
22 
23 private void TxtUser_KeyPress(object sender, KeyPressEventArgs e)
24         {
25             //阻止从键盘输入键
26            e.Handled = true;
27 
28             if ((e.KeyChar >= '0' && e.KeyChar <= '9') || (e.KeyChar == (char)8))
29             {
30 
31                 if ((e.KeyChar == (char)8)) { e.Handled = false; return; }
32                 else
33                 {
34                     int len = TxtUser.Text.Length;
35                     if (len < 5)
36                     {
37                         if (len == 0 && e.KeyChar != '0')
38                         {
39                             e.Handled = false; return;
40                         }
41                         else if(len == 0)
42                         {
43                             MessageBox.Show("编号不能以0开头！"); return;
44                         }
45                         e.Handled = false; return;
46                     }
47                     else
48                     {
49                         MessageBox.Show("编号最多只能输入5位数字！");
50                     }
51                 }
52             }
53             else
54             {
55                 MessageBox.Show("编号只能输入数字！");
56             }
57            
58 
59         }