Binding, Converter, ConverterParameter, and DoubleAnimation

Question

I have a Binding to which I want to pass the value from a DoubleAnimation. Because ConverterParameter is not a Property, how can I use the value from a DoubleAnimation as a ConverterParameter?

Answer 1

Hi,
the ConverterParameter property can not be bound because it is not a dependency property.

Since Binding is not derived from DependencyObject none of its properties can be dependency properties. As a consequence, a Binding can never be the target object of another Binding.

There is however an alternative solution. You could use a MultiBinding with a multi-value converter instead of a normal Binding (you need implement IMultiValueConverter in yours resource "Substring").

  <TextBox>
    <TextBox.Text>
      <MultiBinding Converter="{StaticResource Substring}">
        <Binding Path="Text" ElementName="txtMessage"/>
        <Binding Path="Tag" ElementName="txtMessageOut"/>
      </MultiBinding>
    </TextBox.Text>
  </TextBox>

Answer 2

Hi,
excuse me, here is another approach for UWP.

<Page  
    x:Class="App1.Page15"  
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
    xmlns:local="using:App15"  
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
    mc:Ignorable="d"  
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">  
  <StackPanel>  
    <StackPanel.Resources>  
      <local:MySubstringConverter x:Key="Substring" ConverterParameter="{Binding Tag, ElementName=txtMessageOut}" />  
    </StackPanel.Resources>  
    <TextBox x:Name="txtMessage"/>  
    <TextBox x:Name="txtMessageOut" Tag="end"/>  
    <TextBlock Text="{Binding Text, ElementName=txtMessage, Converter={StaticResource Substring}}"/>  
  </StackPanel>  
</Page>  

And converter:

  public class MySubstringConverter : DependencyObject, IValueConverter  
  {  
    public static readonly DependencyProperty ConverterParameterProperty =  
      DependencyProperty.RegisterAttached("ConverterParameter", typeof(string),  
      typeof(MySubstringConverter), new PropertyMetadata(string.Empty));  
    public static string GetConverterParameter(DependencyObject obj) => obj.GetValue(ConverterParameterProperty) as string;  
    public static void SetConverterParameter(DependencyObject obj, string value) => obj.SetValue(ConverterParameterProperty, value);  
  
    public object ConverterParameter  
    {  
      get { return GetValue(ConverterParameterProperty); }  
      set { SetValue(ConverterParameterProperty, value); }  
    }  
  
    public object Convert(object value, Type targetType, object parameter, string language)  
    {  
      // Converter functionality  
      return (value ?? "").ToString() + " - " + (this.ConverterParameter ?? "").ToString();  
    }  
  
    public object ConvertBack(object value, Type targetType, object parameter, string language)  
    {  
      throw new NotImplementedException();  
    }  
  }  

Result:

Answer 3

That doesn't seem to be working for me. Here is my code:

Public Class SubstringConverter : Inherits DependencyObject : Implements IValueConverter
    Public Shared ReadOnly ConverterParameterProperty As DependencyProperty = DependencyProperty.Register("ConverterParameter", GetType(Integer), GetType(SubstringConverter), New PropertyMetadata(0))

    Public Property ConverterParameter As Object
        Get
            Return GetValue(ConverterParameterProperty)
        End Get
        Set(ByVal value As Object)
            SetValue(ConverterParameterProperty, value)
        End Set
    End Property

    Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
        Return value.ToString().Substring(0, If(Me.ConverterParameter Is Nothing, value.ToString().Length, Math.Min(CInt(Me.ConverterParameter), value.ToString().Length)))
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
        Return String.Empty
    End Function
End Class

<ctrl:SubstringConverter x:Key="Substring" ConverterParameter="{Binding Tag,ElementName=txtMessageOut}"/>

<TextBlock x:Name="txtMessageOut" Tag="3" Text="{Binding Text,ElementName=txtMessage,Converter={StaticResource Substring}}"/>

If I use a literal for ConverterParameter it works. I used a regular DependencyProperty because it didn't look like an Attached one (is there a reason for an attached property?). Am I doing something wrong?

Answer 4

Hi,
try this code. Your code doesn't work. Check this code:

PropertyMetadata(String.Empty)

Return value.ToString().Substring(0, If(Me.ConverterParameter Is Nothing, value.ToString().Length, Math.Min(CInt(Me.ConverterParameter), value.ToString().Length)))

  Public Class MySubstringConverter
    Inherits DependencyObject
    Implements IValueConverter

    Public Shared ReadOnly ConverterParameterProperty As DependencyProperty =
      DependencyProperty.RegisterAttached("ConverterParameter", GetType(String),
      GetType(MySubstringConverter), New PropertyMetadata(String.Empty))
    Public Shared Function GetConverterParameter(obj As DependencyObject) As String
      obj.GetValue(ConverterParameterProperty).ToString()
    End Function
    Public Shared Sub SetConverterParameter(obj As DependencyObject, value As String)
      obj.SetValue(ConverterParameterProperty, value)
    End Sub

    Public Property ConverterParameter As Object
      Get
        Return GetValue(ConverterParameterProperty)
      End Get
      Set(value As Object)
        SetValue(ConverterParameterProperty, value)
      End Set
    End Property

    Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
      Return If(value Is Nothing, "", value.ToString()) & " - " & If(Me.ConverterParameter Is Nothing, "", Me.ConverterParameter.ToString())
      'Return value.ToString().Substring(0, If(Me.ConverterParameter Is Nothing, value.ToString().Length, Math.Min(CInt(Me.ConverterParameter), value.ToString().Length)))
    End Function

    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.ConvertBack
      Throw New NotImplementedException()
    End Function
  End Class

Try this Convert function:

Public Function Convert(value As Object, targetType As Type, parameter As Object, language As String) As Object Implements IValueConverter.Convert
  Dim v = value.ToString
  Dim l1 = v.Length
  Dim l2 As Integer = 0
  If Me.ConverterParameter IsNot Nothing AndAlso Integer.TryParse(Me.ConverterParameter.ToString, l2) Then
    l1 = Math.Min(l2, l1)
  End If
  Return v.Substring(0, l1)
End Function