编制计算类程序时文本框一般都用于输入数字数据，此时可以通过以下步骤来确保用户输入数据的正确性：
首先添加好文本框控件TextBox后把属性IMEMode的值改成Disable，这样在该文本框中就不能使用中文输入法了。然后对文本框的KeyPress事件添加以下代码
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
If Char.IsDigit(e.KeyChar) Or e.KeyChar = Chr(8) Then
e.Handled = False
Else
e.Handled = True
End If
End Sub
其中e.KeyChar是键盘输入的键对应的字符，IsDigit函数可以判断是否为0到9的数字，Chr(8)为退格键，当e.Handled为True时，程序认为该KeyPress事件已经被处理过了，文本框的内容也就不会发生变化了。从以上程序中不难看出，此时文本框只能接受数字和退格键，也就是说这个文本框是用来输入整数的。
如果文本需要输入小数的话，就要能够输入小数点"."，而且小数点只能输入一次，此时可以将上面的函数改为下面的格式：
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
If Char.IsDigit(e.KeyChar) Or e.KeyChar = Chr(8) Or e.KeyChar = "." Then
If e.KeyChar = "." And InStr(TextBox1.Text, ".") > 0 Then
e.Handled = True
Else
e.Handled = False
End If
Else
e.Handled = True
End If
End Sub
其中函数InStr返回指定字符在字符串中的位置，当字符串中不含此字符时，返回一个负数。这时文本框可以用来输入正整数及小数。
如果文本需要输入负数的话，就要能够输入负号"-"，而且只能是文本框输入的第一个字符，此时又可以将上面的函数改为下面的格式：
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
If Char.IsDigit(e.KeyChar) Or e.KeyChar = "." Or e.KeyChar = Chr(8) Then
If e.KeyChar = "." And InStr(TextBox1.Text, ".") > 0 Then
e.Handled = True
Else
e.Handled = False
End If
ElseIf e.KeyChar = "-" And TextBox1.Text = "" Then
e.Handled = False
Else
e.Handled = True
End If
End Sub
这时文本框可以用来输入正的或负的整数及小数。
当有多个文本框需要做输入限制时，可以在以上代码Handles后面加上多个文本框的KeyPress事件，各事件之间用逗号隔开，例如
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress, Textbox2.KeyPress, Textbox3.KeyPress
对于要判断文本框内容的函数, 就要把代码进行修改, 使其能够同时处理多个文本框, 也就是把上面后两段程序中的TextBox1.Text改为CType(sender, TextBox).Text, 这样一来就能够对号入座了, 比如上面能够输入负号的代码就可以改成
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress, Textbox2.KeyPress, Textbox3.KeyPress
If Char.IsDigit(e.KeyChar) Or e.KeyChar = "." Or e.KeyChar = Chr(8) Then
If e.KeyChar = "." And InStr(CType(sender, TextBox).Text, ".") > 0 Then
e.Handled = True
Else
e.Handled = False
End If
ElseIf e.KeyChar = "-" And CType(sender, TextBox).Text = "" Then
e.Handled = False
Else
e.Handled = True
End If
End Sub
这样一来四个文本框就都只能输入正的或负的整数及小数了。
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Private Sub text1_keypress(ByVal keyascii As Integer)
Select Case keyascii
Case 8, 9, 13, &H30 To &H39, asc("A") To asc("Z"), asc("a") To asc("z")
Case Else
keyascii = 0
End Select
End Sub
Keypress是当键盘按下时触发，Change是在文本框中的字符串变化时触发
Keypress要比change先触发
而且keypress可以用来判断一些非可见字符，如:回车 ch(13)
Private Sub txtSource_KeyPress(ByVal KeyAscii As Integer)
if keyascii=13 then ..........(判断在textbox里是否按下回车键)
End Sub
keypress在调试的时候比较麻烦，注意一下
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Private Sub ButtonItem15_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonItem15.Click
If Me.fDate.TextBox.Text.ToString = "" Then
Me.ErrorProvider1.SetError(Me.fDate.TextBox, "输入天数")
Else
Dim sqlDate As Date
Dim intDate As Integer = "-" + Me.fDate.TextBox.Text.ToString
sqlDate = DateAdd("d", intDate, Now.Date)
'MsgBox(sqlDate)
strSql = "select * from business where shijian <= #" + sqlDate + "#"
MsgBox(strSql)
bindv2(strSql)
End If
End Sub