学生管理系统总结收获——限制字符
一.ASCII码——限制字符问题
在敲学生的时候需要设置很多限制条件，比如限制字符，显示数据类型，限制字符长度等等，其中有很多限制需要通过ASCII码来进行代码编写限制，数不胜数，小编至今还是有很多限制条件的ASCII 不知道，记是永远记不住的，未来用到的时候再多多补充啦。下面是小编在优化学生时经常用到的一些代码限制条件，分享给大家。
1.文本框只能输入汉字：
Private SubtxtDirector_KeyPress(KeyAscii As Integer)
If KeyAscii > 0 And KeyAscii <> 13And KeyAscii <> 8 Then KeyAscii = 0
End Sub
或者：
Private Sub txtusername_KeyPress(KeyAscii As Integer)
If KeyAscii < 0 Or KeyAscii = 8 Or KeyAscii = 13 Then Exit Sub
KeyAscii = 0
End Sub
或者：
Private Sub txtDirector_KeyPress(KeyAscii As Integer)
If KeyAscii < 0 Or KeyAscii = 8 Then Exit Sub
KeyAscii = 0 ‘不能输入
End Sub
2.只能输入文字及删除键：
Private Sub Text1_KeyPress(KeyAscii As Integer)
If KeyAscii >= -20319 And KeyAscii <= -3652 Or KeyAscii = 8 Then
Else
KeyAscii = 0
End If
End Sub
3.限制只能输入数字：
If KeyAscii = 8 Then Exit Sub
If KeyAscii < 48 Or KeyAscii > 57 Then KeyAscii = 04.限制只能输入数字和删除键：
If KeyAscii <> 8 And (KeyAscii < 48 Or KeyAscii > 57) Then
KeyAscii = 0
End if
5.只能输入数字和文字：
If ((KeyAscii <= 57 And KeyAscii >= 48) Or (KeyAscii <= -3652 And KeyAscii >= -20319) Or KeyAscii = 8) = False Then KeyAscii = 06.只能输入数字和英文字母：
Private Sub Text1_KeyPress(KeyAscii As Integer)
If ((KeyAscii >= 48 And KeyAscii <= 57) Or (KeyAscii >= 65 And KeyAscii <= 90) Or (KeyAscii >= 97 And KeyAscii <= 122)) = False Then KeyAscii = 0
End Sub
7.只输入数字、小数和删除键：
If KeyAscii <> Asc(".") And (KeyAscii <> 8) And (KeyAscii < Asc("0") Or KeyAscii > Asc("9")) Then
KeyAscii = 0
End If
'添加成绩窗体限制成绩：
(1)限制添加成绩窗体只能输入数字且大于0小于150且可以使用退格键
If KeyAscii = 8 Then Exit Sub
If KeyAscii < 48 Or KeyAscii > 57 Then
KeyAscii = 0
ElseIf CLng(txtResult.Text & Chr(KeyAscii)) > 100 Or CLng(txtResult.Text & Chr(KeyAscii)) < 0 Then
KeyAscii = 0
End If
(2)'限制文本框只能输入数字和小数点,但是不可以使用退格键
If KeyAscii < 48 Or KeyAscii > 57 Then
If KeyAscii = 46 Then
If txtResult.Text = "" Or InStr(1, txtResult.Text, ".") <> 0 Then
KeyAscii = 0
KeyAscii = 46
End If
Else
KeyAscii = 0
End If
End If
(3)既限制只输入数字、小数点、又可以限制数值大小，也可以使用退格键
If KeyAscii <> Asc(".") And (KeyAscii <> 8) And (KeyAscii < Asc("0") Or KeyAscii > Asc("9")) Then
KeyAscii = 0
ElseIf CLng(txtResult.Text & Chr(KeyAscii)) > 100 Or CLng(txtResult.Text & Chr(KeyAscii)) < 0 Then
KeyAscii = 0
End If
8.只能输入文字，英文和空格：
Private Sub txtName_Change()
txtName.MaxLength = 10 '限制长度为10
End Sub
Private Sub txtName_KeyPress(KeyAscii As Integer)
If ((KeyAscii <= -3652 And KeyAscii >= -20319) Or (KeyAscii >= 65 And KeyAscii <= 90) Or (KeyAscii >= 97 And KeyAscii <= 122) Or KeyAscii = 32 Or KeyAscii = 8) = False Then
KeyAscii = 0
End If
End Sub
9.限制只能输入英文字母、数字以及退格：
Private Sub txtUserName_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case 48 To 57 '只能输入数字
Case 65 To 90 '只能输入大写字母
Case 97 To 122 '只能输入小写字母
Case 8 '只能输入退格
Case Else '否则
KeyAscii = 0 '限制输入，使输入无效
End Select
End Sub
'限制了用户名只能输入数字，大小写字母和删除键，其他输入均被视为无效输入。10.限制特殊字符、数字、空格，只能输入汉字和字母
Private Sub txtCoursename_KeyPress(KeyAscii As Integer)
If KeyAscii < 0 Or KeyAscii = 8 Or KeyAscii = 13 Then
ElseIf Not Chr(KeyAscii) Like "[a-zA-Z]" Then
KeyAscii = 0
End If
End Sub
11.文本框限制特殊字符不可输入：
Private SubtxtClassroom_KeyPress(KeyAscii As Integer)
If ((KeyAscii >= 48 And KeyAscii <=57) Or (KeyAscii >= 65 And KeyAscii <= 90) Or _
(KeyAscii >= 97 And KeyAscii <=122) Or (KeyAscii = 8)) = flase Then KeyAscii = 0
End Sub12.限制出生日期晚于入学日期：
Dim borndate As Date
Dim getdate As Date'定义变量
borndate =Trim(txtBorndate.Text)
getdate =Trim(txtRudate.Text)
If getdate<=borndate then'进行比较
MsgBox"入学时间不能早于出生时间，请重新输入",vbOKOnly + vbInformation,"警告"
txtRudate.SetFocus
Exit Sub
End If 13.限制文本框输入内容的长度
txtClassno.MaxLength = 1014.限制文本框输入内容的数值范围
If Val(txtClassno.Text) > 2147483647 Or Val(txtClassno.Text) < 1Then
MsgBox "输入数值在1到2147483647范围内"
txtClassno.SetFocus
Exit Sub
End If以上内容是小编站在巨人的肩膀上学习和收获到的，感谢走在前边的大佬们，默默无言的给我提供了太多太多的帮助，让我可以走的更加的稳重，善于学习和应用并且不断总结和整理，把知识慢慢积累起来，一点一点的成长吧！