Looking to improve my custom web control textbox for percentages.

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VB

ASP.NET

Hello wonderful people of Code Project!

So here's my situation:

I have a custom textbox web control I've made that is designed to accept user input of a percentage and store them in its decimal equivalence (e.g. "13.5" => "0.135"). Simillarly, when the textbox is bound it will take the decimal value from the datasource and display it as its percentage equivalence (e.g. "0.135" => "13.5").

<DefaultProperty("Text"),
ToolboxData("<{0}:PercentageTextBox  runat="server"></{0}:PercentageTextBox>")> _
Public Class PercentageTextBox
    Inherits TextBox
    Implements IValidator

#Region "Properties"
    Public Property Editable As Boolean
    Private ReadOnly Property InputFormatType As PercentageType
        Get
            Return PercentageType.InPercent ''Can be InDecimal if required
        End Get
    End Property

    <Bindable(True),
    Category("Appearance"),
    DefaultValue(""),
    Description("The name of the percentage"),
    DesignerSerializationVisibility(DesignerSerializationVisibility.Content),
    PersistenceMode(PersistenceMode.InnerProperty)>
    Public Overridable Property Name As String

    <Bindable(True),
    Category("Appearance"),
    DefaultValue(""),
    Localizable(True)>
    Overrides Property Text() As String
        Get
            Dim s As String = CStr(ViewState("Text"))

            If s Is Nothing Then
                Return String.Empty
            Else
                Return s
            End If
        End Get

        Set(ByVal Value As String)
            Dim output As String = Value
            Try
                ''Convert percentage input to decimal.
                Dim TextVal = CDec(Value)
                Dim converted As New PercentageValue(TextVal, _
                                                     PercentageType.InDecimal)
                output = CStr(converted.Value)
            Catch ex As Exception
                output = Value
            Finally
                ViewState("Text") = output
            End Try
        End Set
    End Property
#End Region

    Protected Overrides Sub Render(writer As HtmlTextWriter)
        Try
            If Editable Then
                ''Convert decimal value to percentage
                Dim val = CDec(ViewState("Text"))
                val = System.Math.Round(val * 10000, 2)
                ViewState("Text") = val
            End If

        Catch ex As Exception
            ''Do something?
        Finally
            MyBase.Render(writer)
        End Try
    End Sub
End Class

N.B. I stripped out the validation code added to this control; also, you don't see the math in the control itself for converting the input as it uses the class PercentageValue to convert the value based upon the enumerator PercentageType. The idea behind this was that this could be interacted with to switch method based on the InputFormatType property in the future.

Now this is my first custom control I've made so I'm willing to try and improve how this works:

Firstly: I am not sure about where my conversion takes place in the control. Should I be doing the input conversion in the Text() method and the inverse in the Render() method. Reason I say this is that when the control is editing a stored value the Set property is called unnecessarily (resulting in my conversion in Render() having to x10000 to undo the previous set call).

Secondly: I've creating the property Editable which needs to be set manually when I use the control, such as in an EditItemTemplate in a DetailsView. This is to distinguish it from a user inputting a new value. Is there some property of the inherited textbox that I can infer this from instead of having to set it as such manually?

Any pointers or advice would be much appreciated.

Thanks,