1. 该判断事件是TextBox的keypress 事件中进行判断的
2. 判断key（e.KeyChar）是不是数字、小数点、或者负号
3. 判断是否多次输入负号或者小数点
代码如下：
If IsNumeric(e.KeyChar) OrElse e.KeyChar = "." OrElse e.KeyChar = "-" Then
Dim strCash As String =TextBox1.Text
If strCash.Contains(".") Then
If strCash.Split(".").Length > 2 Then
e.Handled = True
End If
End If
If strCash.Contains("-") Then
If strCash.Split("-").Length > 2 Then
e.Handled = True
End If
If strCash.Substring(0,1) <> "-" Then
e.Handled = True
End If
If strCash.Length > 1 Then
If strCash.Substring(1,1) = "." Then
e.Handled = True
End If
End If
End If
ElseIf Not Asc(e.KeyChar) = Keys.Back Then
e.Handled = True
End If