Label with static text and binding

Question

I am trying to get a label to show specific text while also being bound to a variable in the VB.Net code. I can make a binding but I cant get it to add the static text.

What I have so far:

<Label x:Name="TestLabel" Content="{Binding Path=Row, StringFormat='Row #{0}'}" 
                          HorizontalAlignment="Left" 
                          Height="35" 
                          Margin="203,21,0,0" 
                          VerticalAlignment="Top" 
                          Width="83" 
                          FontSize="18">

with

Public Class Row
    Implements INotifyPropertyChanged

    Private _Row As Byte
    Public Property Row() As Byte
        Get
            Return _Row
        End Get
        Set(ByVal value As Byte)
            _Row = value

            OnPropertyChanged(New PropertyChangedEventArgs("Row"))
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Public Sub OnPropertyChanged(ByVal e As PropertyChangedEventArgs)
        If Not PropertyChangedEvent Is Nothing Then
            RaiseEvent PropertyChanged(Me, e)
        End If
    End Sub
End Class

and

Private Rows As New Row

Public Sub New()
    InitializeComponent()
    TestLabel.DataContext = Rows
    Rows.Row = MyTextBox.Text.HandledStringtoSByte
End Sub

The extension code (since I have a custom extension):

''' <summary>
''' Handles conversion of string variable to Tiny Integer
''' </summary>
''' <param name="s"></param>
''' <param name="I">Returned if conversion fails.</param>
''' <returns>Signed 8bit Integer</returns>
''' <remarks></remarks>
<Runtime.CompilerServices.Extension()> _
Public Function HandledStringtoSByte(ByRef S As String, Optional I As SByte = 0) As SByte
    Try
        If S = String.Empty Then
            Return I
        Else
            Return SByte.Parse(S)
        End If
    Catch
        Dim result As String = String.Empty
        Dim ReturnByte As SByte
        Dim Parsed As Byte
        For Each Character In S.ToCharArray
            If Character = "-" Then
                If S.Substring(0, 1).ToString <> "-" Then
                    Exit For
                End If
            End If
            If Character = "." Then
                Exit For
            End If
            If Byte.TryParse(Character, Parsed) Then
                result = result + Parsed.ToString
            End If
        Next
        If result <> String.Empty Then
            If SByte.TryParse(result, ReturnByte) Then
                Return SByte.Parse(ReturnByte)
            Else
                If Short.Parse(result) > Short.Parse(SByte.MaxValue.ToString) Then
                    Return SByte.MaxValue
                ElseIf Short.Parse(result) < Short.Parse(SByte.MinValue.ToString) Then
                    Return SByte.MinValue
                Else
                    Return SByte.Parse(ReturnByte)
                End If
            End If
        Else
            Return I
        End If
    End Try
End Function

Now I thought that using the stringformat in binding would add the static text and place the bound variable into the {0} spot but all is gives me is the bound variable in the label.

What am i doing wrong?

Answer 1

Binding target is Content property which is Object type, that is why you cannot use StringFormat with binding.

Instead use ContentStringFormat property

<Label Content="{Binding Path=Row}"  
       ContentStringFormat="Row #{0}" />

Another approach: create readonly property in the ViewModel which will represent value in wanted format

Private _Row As Byte
Public Property Row() As Byte
    Get
        Return _Row
    End Get
    Set(ByVal value As Byte)
        _Row = value
        OnPropertyChanged(New PropertyChangedEventArgs("Row"))
        OnPropertyChanged(New PropertyChangedEventArgs("RowText"))
    End Set
End Property

Public ReadOnly Property RowText As String
    Get
        Return String.Format("Row #{0}", Me.Row)
    End Get
End Property

Then bind this property to the View

<Label Content="{Binding Path=RowText}"/>

Answer 2

The problem is that Binding.StringFormat is "a string that specifies how to format the binding if it displays the bound value as a string". In practice it seems to work only if the target property is of type string - as you pointed out it's working for TextBlock.Text (which is of type string) and not for Label.Content (which is of type object). There are several ways to approach this problem, one of them would be to nest a TextBlock in the Content property:

<Label>
    <TextBlock Text="{Binding Path=Row, StringFormat='Row #{0}'}" />
</Label>

This doesn't really introduce any additional complexity to the visual tree since strings are by default presented by TextBlocks.

Otherwise you could create your own converter, or you could go with Fabio's solution and utilize Label.ContentStringFormat property.