如何允许用户只在vb.net的文本框中输入数字？

Question

How can I prevent the user to enter characters but only numbers and '.' in a textbox in vb.net 2005?

Answer 1

The following will allow you to test for specific key values (from http://www.daniweb.com/forums/thread127299.html ):

Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
    If (Microsoft.VisualBasic.Asc(e.KeyChar) < 48) _
              Or (Microsoft.VisualBasic.Asc(e.KeyChar) > 57) Then
            e.Handled = True
    End If
    If (Microsoft.VisualBasic.Asc(e.KeyChar) = 8) Then
            e.Handled = False
    End If
End Sub

If this isn't what you are looking for, try the isNumeric() function.

Answer 2

Just to help, I had a snippet which I was making for a calculator which may help, it allows Delete, Backspace, Digits and the '.' char. You can also add in a call to a function to process the text box on the pressing of the Enter key.

  Private Sub Box_Input_KeyDown(ByVal sender As Object, _
                                ByVal e As System.Windows.Forms.KeyEventArgs) _
                                Handles Box_Input.KeyDown



    If Char.IsDigit(Chr(e.KeyValue)) Or _
       Chr(e.KeyValue) = "¾"c Or _
       e.KeyData = Keys.Delete Or _
       e.KeyData = Keys.Back Then

        If Chr(e.KeyValue) = "¾"c Then
            If Box_Input.Text.Contains(".") Then
                e.SuppressKeyPress = True
            Else
                e.SuppressKeyPress = False
            End If
        End If
    ElseIf e.KeyData = Keys.Enter Then
         `State a call to function for when Enter is pressed`
    Else
        e.SuppressKeyPress = True
    End If

End Sub

This code allows entry of all numbers, the back space and delete keys as well as only allowing one '.' in the text. An idea might be to add the TAB function to allow Tab stops.

Answer 3

Dim num1 As Integer

Try   

   num1 = Cint(TextBox1.Text)

Catch ex As Exception

   TextBox1.Clear()    
   TextBox1.Focus()

End Try

For Single Numbers you may use num1 = Csng(textbox1.text)

Answer 4

try this;

 Dim Validinputchar = "0123456789." + vbBack

    If Not Validinputchar.Contains(e.KeyChar) Then

        e.KeyChar = Nothing

    End If

The Validinputchar variable contains only the characters you want a user to enter in a textbox.

Note: the code should be placed under the textbox_keypress event

Answer 5

Try this:

Sub TB_Press(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
    If Not Char.IsDigit(e.KeyChar) AndAlso Not Char.IsControl(e.KeyChar) Then
        e.Handled = True
    End If
End Sub

But this allow only numbers, and you may what to admit decimal digits adding this condition:

If e.KeyChar <> decSeparator AndAlso _
                     Not CType(sender, TextBox).Text.Contains(decSeparator) Then

You can get the decimal separator with:

Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSepar‌​ator

---

Another simple option is to do this:

Sub TB_Press(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
    Dim text As String = Ctype(sender, TextBox).Text
    e.Handled = Double.TryParse(text, New Double)
End Sub

Answer 6

I wrote a fool proof routine that eliminates the Alpha characters and allows all of the others.

You could technically put any character you want in the string to prevent it from being entered like punctuation marks.

    Private Sub checkIfNumber(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles tbReOrderAmount.KeyDown

    Dim disallowedKeys As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
    If Boolean.Parse(disallowedKeys.Contains(e.KeyCode.ToString)) Then
        e.SuppressKeyPress = True
    End If
End Sub

This is a nice clean simple way of preventing any character in the disallowedKeys string from being entered in any textbox or field you choose, just have the KeyDown event of the control reference this method.

Answer 7

Here is the Better Answer in My Opinion:

   Private Sub txtScale_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtScale.KeyPress
          If IsNumeric(txtScale.Text + e.KeyChar) = False Then e.Handled = True
   End Sub

Cheers,Sach

Answer 8

After searching through several results here on stackoverflow and elsewhere I wasn't satisfied with the solutions I found: they all had drawbacks of some sort, mostly keyboard layout issues or incorrect handling of control keys, eg Ctrl+C wasn't possible anymore.

The solutions I tried all went for the KeyDown/Up approach; I decided to try the TextChanged event and implementing the simple logic: if the current input doesn't validate, then replace it with the old value; else: update the old value.

Of course - as always - implementing the feature details turned out to be a bit more complex :o| ...but in the end I now have a TextBox that can be limited to integer or double values within a specified range and that has a new event, ApplyValue, that can be listened to - instead of TextChanged or Validated - which is fired depending on the chosen style, ie numeric values shouldn't fire events while typing, but for some text values it may be desirable.

'nuff said, here's the full code of the control that I'd like to share with the absolutely amazing stackoverflow community - my first contribution ;o) I hope it can be of some use to someone!

Imports System.ComponentModel

Public Class RestrictedTextbox
    Inherits Windows.Forms.TextBox

#Region "Constructor, StyleEnum, ApplyValue event"
    Public Sub New()
        MyBase.New()
    End Sub

    'use enum instead of flags because of the overhead for creating a UiTypeEditor
    Public Enum StyleEnum
        [Integer]
        IntegerZero
        [Double]
        DoubleZero
        TextOnChange
        TextOnValidate
    End Enum

    Public Event ApplyValue(sender As Object, e As System.EventArgs)
#End Region

#Region "New Properties"
    Private _style As StyleEnum = StyleEnum.TextOnValidate
    <Category("Restrictions"), _
     Description("Determines input validation, alignment and when the ApplyValue event is raised"), _
     Browsable(True), DefaultValue(StyleEnum.TextOnValidate)> _
    Public Shadows Property Style As StyleEnum
        Get
            Return _style
        End Get
        Set(value As StyleEnum)
            _style = value

            initializeText()
        End Set
    End Property

    Private _min As Integer = 0
    <Category("Restrictions"), _
     Description("Minimum value (for numeric styles)"), _
     Browsable(True), DefaultValue(0)> _
    Public Property Minimum As Integer
        Get
            Return _min
        End Get
        Set(value As Integer)
            _min = value

            initializeText()
        End Set
    End Property

    Private _max As Integer = 2147483647
    <Category("Restrictions"), _
     Description("Maximum value (for numeric styles)"), _
     Browsable(True), DefaultValue(2147483647)> _
    Public Property Maximum As Integer
        Get
            Return _max
        End Get
        Set(value As Integer)
            _max = value

            initializeText()
        End Set
    End Property
#End Region

#Region "Shadow properties"
    'hide and do not allow changing
    <Browsable(False), EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
    Public Shadows Property TextAlign As Windows.Forms.HorizontalAlignment
        Get
            Return MyBase.TextAlign
        End Get
        Set(value As Windows.Forms.HorizontalAlignment)
            'do nothing
        End Set
    End Property

    'hide and always use false
    <Browsable(False), EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
    Public Shadows Property Multiline As Boolean
        Get
            Return False
        End Get
        Set(value As Boolean)
            MyBase.Multiline = False
        End Set
    End Property

    'hide and always use true
    <Browsable(False), EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
    Public Shadows Property CausesValidation As Boolean
        Get
            Return True
        End Get
        Set(value As Boolean)
            MyBase.CausesValidation = True
        End Set
    End Property

    'hide, but emulate default
    <Browsable(False), EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
    Public Shadows Property Lines As String()
        Get
            Return MyBase.Lines
        End Get
        Set(value As String())
            MyBase.Lines = value
        End Set
    End Property
#End Region

#Region "validateText, initializeText"
    Private _oldText As String = ""
    Private nfi As System.Globalization.NumberFormatInfo = New System.Globalization.NumberFormatInfo With {.CurrencyDecimalSeparator = "."}

    Private Sub initializeText()
        Dim def As String = ""

        Select Case _style
            Case StyleEnum.TextOnChange, StyleEnum.TextOnValidate
                MyBase.TextAlign = HorizontalAlignment.Left
                def = ""

            Case StyleEnum.Double, StyleEnum.Integer
                MyBase.TextAlign = HorizontalAlignment.Right
                def = ""

            Case StyleEnum.DoubleZero, StyleEnum.IntegerZero
                MyBase.TextAlign = HorizontalAlignment.Right
                If _min < 0 And _max > 0 Then
                    def = "0"
                Else
                    def = _min.ToString
                End If

        End Select

        If Me.Text = "" Or Me.Text = "0" Or Not Me.validateText Then
            Me.Text = def
        End If
    End Sub


    Private Function validateText() As Boolean
        Dim negativeOk As Boolean = False
        Dim checkDouble As Boolean = False
        Dim checkInteger As Boolean = False
        Dim valueOk As Boolean = False

        Select Case _style
            Case StyleEnum.Double, StyleEnum.DoubleZero
                checkDouble = True

            Case StyleEnum.Integer, StyleEnum.IntegerZero
                checkInteger = True

            Case StyleEnum.TextOnChange, StyleEnum.TextOnValidate
                valueOk = True
        End Select

        If Not valueOk Then
            Dim txt As String = Me.Text
            If String.IsNullOrEmpty(txt) Then
                valueOk = True
            ElseIf _min < 0 And txt = "-" Then
                valueOk = True
            Else
                Dim tmp As Double = 0
                If checkDouble Then
                    valueOk = Double.TryParse(txt, Globalization.NumberStyles.Float, nfi, tmp)
                ElseIf checkInteger Then
                    valueOk = Integer.TryParse(txt, Globalization.NumberStyles.Float, nfi, tmp)
                End If

                If valueOk And ((tmp > _max) Or ((tmp < _min) And (tmp.ToString.Length >= _min.ToString.Length))) Then
                    'if value could be parsed, but
                    'value is too large or
                    'value is too small, even though the length is sufficient (to allow entering incomplete numbers, e.g. "2", if _min=10)
                    'NOTE: too small numbers will be caught in validation event
                    valueOk = False
                End If
            End If
        End If

        Return valueOk
    End Function
#End Region

#Region "Events"
    Private Sub WdTextbox_TextChanged(sender As Object, e As EventArgs) Handles Me.TextChanged
        Dim valueOk As Boolean = Me.validateText

        If Not valueOk Then
            Dim oldPos As Integer = Me.SelectionStart
            Me.Text = _oldText
            If (oldPos > 0) Then
                Me.SelectionStart = oldPos - 1
            End If
        Else
            Me._oldText = Text

            If Me._style = StyleEnum.TextOnChange Then
                RaiseEvent ApplyValue(Me, New System.EventArgs)
            End If
        End If
    End Sub

    Private Sub WdTextbox_Validating(sender As Object, e As CancelEventArgs) Handles Me.Validating
        Dim txt As String = Me.Text
        Dim raise As Boolean
        Select Case _style
            Case StyleEnum.Double, StyleEnum.Integer
                Dim tmp As Double = 0
                If Double.TryParse(txt, Globalization.NumberStyles.Float, nfi, tmp) Then
                    If tmp < _min Then
                        tmp = _min
                    ElseIf tmp > _max Then
                        tmp = _max
                    End If

                    Me.Text = IIf(tmp <> 0, tmp.ToString, "")
                Else
                    Me.Text = ""
                End If
                raise = True

            Case StyleEnum.DoubleZero, StyleEnum.IntegerZero
                Dim tmp As Double = 0
                If Double.TryParse(txt, Globalization.NumberStyles.Float, nfi, tmp) Then
                    If tmp < _min Then
                        tmp = _min
                    ElseIf tmp > _max Then
                        tmp = _max
                    End If

                    Me.Text = tmp.ToString
                Else
                    Me.Text = "0"
                End If
                raise = True

            Case StyleEnum.TextOnChange
                raise = False

            Case StyleEnum.TextOnValidate
                raise = True
        End Select

        If raise Then
            RaiseEvent ApplyValue(Me, New System.EventArgs)
        End If
    End Sub
#End Region

End Class

Answer 9

• First, add a TextBox.
• Second, Change the event from TextChanged to KeyPress .
• You see it at the upper right of your field codes, then click the small arrow.

• Populate this codes between your TextBox1_KeyPress

    If Char.IsDigit(e.KeyChar) = False And Char.IsControl(e.KeyChar) = False Then e.Handled = true MsgBox("Please enter a valid number") End If 

• I hope it can help you this simple codes
• for more information http://audzkie.barsalote@gmail.com

Answer 10

You could use the KeyDown event to check if the value of the key pressed is numeric or '.' and set the event property handled to true whenever the input is numeric or '.'. (I might be wrong with the value of the handled property since i don't remember if it was true or false that discarded the event and hindered the key to be input into the textbox)

Answer 11

Look at the ErrorProvider . Using that you can prevent focus from leaving control until correct value is entered, at the same time allowing user to press cancel or dialog close buttons.

Answer 12

This works

Private Sub txt1_PreviewTextInput(sender As Object, e As TextCompositionEventArgs) Handles txt1.PreviewTextInput
   e.Handled = Not IsNumeric(e.Text)
End Sub