NumericTextBox class

I've been reading a number of topics recently where people were using text boxes for input of numeric values.
Everyone kept using CInt or CDbl to obtain values which is generally a bad form since a user can provide the wrong input (i.e. text instead of digits).

To help the beginners (or just lazy people) to properly validate user input I've extended a textbox control to provide such people with a ready-to-use solution.

This class can process input from any cultures (in my coutry, for example, we use comma as a delimeter between the integer and fractional parts of a number, in some countries they use dot and god knows who uses what elsewhere).

This class utilizes Globalization NumberFormatInfo to get the Format Provider, suitable for the current system.

Also, this control has properties to assign background colors separately for successfully validated and not validated values.

Also, there are properties that allow validation of Integer values only (if you don't need decimal values). Note: change the type from Decimal to Double if you like.

Also, there is a property that can prevent a user to change focus (to cancel the validation) if he or she made the wrong input.

And finally, there is a property that treats an empty string as zero (default value is true).

http://xmages.net/upload/14b3f6eb.jpg

Basically I would like you to try it out and give me some feedback if possible.

vb.net Code:

''' <summary>
''' Extends the texbox with the Decimal and / or Integer validation
''' And provides users with Value and ValueInt properties that return
''' validated decimal or integer values.
''' </summary>
''' <remarks>
''' * To turn off decimal validation turn ValidateIntOnly 
'''   property to True (default is false).
''' * To prevent user from changing focus with not validated input set 
'''   the CancelValidationOnFail property to True (default is false).
''' * To Get the decimal value use the Value property.
''' * To Get the integer value use the ValueInt property.
''' </remarks>
Class NumericTextbox
 
    Inherits TextBox
 
    'Private members
    Private _Validated As Boolean = False
    Private _IntOnly As Boolean = True
    Private _ShouldCancelValidattion As Boolean = False
    Private _TreatEmptyAsZero As Boolean = True
    Private _Value As Decimal
    Private _IntValue As Integer
 
 
    Private _NotValidatedBackColor As Color = Color.Pink
    Private _ValidatedBackColor As Color = Color.PaleGreen
 
    ''' <summary>
    ''' Occurs between Validating and Validated events if the validation failed.
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Public Event NotValidated(ByVal sender As Object, ByVal e As System.EventArgs)
 
    Public Sub New()
        MyBase.New()
        MyBase.CausesValidation = True
    End Sub
 
    Public Overrides Property Multiline() As Boolean
        Get
            Return MyBase.Multiline
        End Get
        Set(ByVal value As Boolean)
            If value Then
                Throw New NotSupportedException("Multiline mode is not supported")
            End If
        End Set
    End Property
 
 
 
    ''' <summary>
    ''' Gets or sets the setting indicating whether the control should treat an empty string as zero. Default is True.
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Property TreatEmptyAsZero() As Boolean
        Get
            Return _TreatEmptyAsZero
        End Get
        Set(ByVal v As Boolean)
            _TreatEmptyAsZero = v
            Call Me.OnTextChanged(Nothing)
        End Set
    End Property
 
    ''' <summary>
    ''' Gets or sets the background of the control when the value is not validated.
    ''' </summary>
    ''' <remarks>Overrides the BackGound property. the default value is Color.Pink</remarks>
    Public Property NotValidatedBackColor() As Color
        Get
            Return _NotValidatedBackColor
        End Get
        Set(ByVal v As Color)
            _NotValidatedBackColor = v
            MyBase.BackColor = v
            MyBase.Invalidate()
        End Set
    End Property
 
    ''' <summary>
    ''' Gets or sets the backgound of the control when the value has been validated.
    ''' </summary>
    ''' <remarks>The default value is Color.PaleGreen</remarks>
    Public Property ValidatedBackColor() As Color
        Get
            Return _ValidatedBackColor
        End Get
        Set(ByVal v As Color)
            _ValidatedBackColor = v
            MyBase.BackColor = v
            MyBase.Invalidate()
        End Set
    End Property
 
 
    ''' <summary>
    ''' Turns off Decimal validation and validates integers only.
    '''     ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks>Value property will return a rounded decimal.
    ''' To get an integer value use <see cref="ValueInt">ValueInt property</see>.</remarks>
    Public Property ValidateIntOnly() As Boolean
        Get
            Return _IntOnly
        End Get
        Set(ByVal v As Boolean)
            _IntOnly = v
        End Set
    End Property
 
    ''' <summary>
    ''' Gets a decimal value of the validated user input.
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks>Read only</remarks>
    Public ReadOnly Property Value() As Decimal
        Get
            Return _Value
        End Get
    End Property
 
    ''' <summary>
    ''' Gets an integer values of the valdated user input.
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks>To get the decimal value use <see cref="Value">Value property</see></remarks>
    Public ReadOnly Property ValueInt() As Integer
        Get
            If Not _IntOnly Then
                Throw New InvalidOperationException("ValidateIntOnly property is set to false. Set it to true to turn on the integer evaluation.")
                Exit Property
            End If
            Return _IntValue
        End Get
    End Property
 
    ''' <summary>
    ''' Gets or sets a setting indicating whether the control should cancel validation of a control.
    '''     ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks>When set the control won't allow to change focus if the input value is in the wrong formst.</remarks>
    Public Property CancelValidationOnFail() As Boolean
        Get
            Return _ShouldCancelValidattion
        End Get
        Set(ByVal v As Boolean)
            _ShouldCancelValidattion = v
        End Set
    End Property
 
 
    ''' <summary>
    ''' Raises Validating event or cancels Validation if CancelValidationOnFail property is set to true
    ''' </summary>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Protected Overrides Sub OnValidating(ByVal e As System.ComponentModel.CancelEventArgs)
        If ValidateValue() Then
            MyBase.OnValidating(e)
        Else
            e.Cancel = _ShouldCancelValidattion
            MyBase.OnValidating(e)
            RaiseEvent NotValidated(Me, New System.EventArgs)
        End If
    End Sub
 
    Protected Overrides Sub OnTextChanged(ByVal e As System.EventArgs)
        If ValidateValue() Then
            Me.BackColor = _ValidatedBackColor
        Else
            Me.BackColor = _NotValidatedBackColor
        End If
        MyBase.OnTextChanged(e)
        Me.Invalidate()
    End Sub
 
    Protected Overridable Function ValidateValue() As Boolean
        ' Allows any format to be converted to decimal
        Dim ValidationText As String = MyBase.Text
 
        ' Check whether we should trean an empty string as zero
        If MyBase.Text.Length = 0 AndAlso Me._TreatEmptyAsZero Then ValidationText = "0"
 
        Dim fp As IFormatProvider = System.Globalization.NumberFormatInfo.InvariantInfo
        If Not _IntOnly Then
            Return Decimal.TryParse(ValidationText, System.Globalization.NumberStyles.Any, fp, _Value)
        Else
            Return Integer.TryParse(ValidationText, System.Globalization.NumberStyles.Integer, fp, _IntValue)
            _Value = CDec(_IntValue)
        End If
    End Function
 
End Class