Question

I am trying to set twoway binding on a UserControl that I have created.

When I use the control in Xaml is set the DataContext like so…

<uc:MyUserControl DataContext="{Binding Path=MyObject, Mode=TwoWay}" />

My user control is defined as the following….

<UserControl x:Class="SilverlightApplication1.XText"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBox x:Name="Text" Text="{Binding}"/>

    </Grid>
</UserControl>

The data is displayed correctly, however if I make I change I wanted it to update with TwoWay binding.

I have tried this below, but it errors at runtime since no Path is defined.

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBox x:Name="Text" Text="{Binding Mode=TwoWay}"/>

    </Grid>
</UserControl>

Any ideas on how to get the control inside the usercontrol to twoway bind to the DataContext?

Answer 1

I have found a solution that doesn’t require you to give a name to the base control.
When I defined a name for the base UserControl it was creating issues for me when I was adding multiple instances to my Grid, since they were defined as the same name.

This is a combination of my first answer and Doug’s answer.
Note the UserControl lacks the name property and the TextBox has no Binding declared in the XAML

XAML

<UserControl 
    x:Class="SilverlightApplication1.XText"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" 
    d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBox x:Name="MyText"/>    
    </Grid>
</UserControl>

CodeBehind

public partial class XText
{
    public XText()
    {
       InitializeComponent();
       MyText.SetBinding(TextBox.TextProperty, new Binding() 
       { 
          Source = this,  
          Path = new PropertyPath("Value"), 
          Mode = BindingMode.TwoWay
       });
    }


    public static DependencyProperty ValueProperty =
        DependencyProperty.Register(
            "Value",
            typeof(string),
            typeof(XText),
            new PropertyMetadata(null)
        );

    public string Value
    {
        get { return ((string)(GetValue(ValueProperty))); }
        set { SetValue(ValueProperty, value); }
    }

    ...
}

When you are ready to use it do the following

<uc:XText Value="{Binding Path=MyObject, Mode=TwoWay}" />