主题：自定义用户管理例子中的这个情况怎么解决？

1、没必要允许直接输入

2、如果你一定要允许直接输入，可以在确定按钮，判断输入的用户是否存在：

Dim UserName As String = e.Form.Controls("UserName").Value
Dim cmd As New SQLCommand
Dim dt As DataTable
Dim dr As DataRow
cmd.ConnectionName = "User"
If UserName = "" Then
    Messagebox.show("请选择用户!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
    Return
End If
cmd.CommandText = "Select * From {Users} Where [Name] = '" & UserName & "'"
dt = cmd.ExecuteReader

If dt.Datarows.Count = 0 Then

      Messagebox.show("用户不存在!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

      Return
End If
dr = dt.DataRows(0)
If e.Form.Controls("PassWord").Value = dr("Password") Then
    _UserName = UserName
    _UserGroup = dr("Group")
    e.Form.Close
Else
    Messagebox.show("密码错误!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
End If