TextBox in UserControl, can't edit Text dependency property from code behind

Question

My UserControl contains a TextBox and a Button. The TextBox's Text is correctly populated by a dependency property called X.

My Goal: Change the value of X (e.g. Text of the TextBox) when I press the Button.

I have defined the UserControl as follows:

<StackPanel Orientation="Horizontal" >
    <TextBox Name="Xbox" Text="{Binding Path=X}" Width="50"/>
    <Button Content="Current" Click="InsertCurrentBtnClick" />
</StackPanel>

With codebehind:

    public double X
    {
        get { return (double)GetValue(XProperty); }
        set { SetValue(XProperty, value); }
    }

    public static readonly DependencyProperty XProperty =
        DependencyProperty.Register("X", typeof(double), typeof(MyUserControl), new PropertyMetadata(0.0));


    private void InsertCurrentBtnClick(object sender, RoutedEventArgs e)
    {
        X = 0.7;

        //BindingOperations.GetBindingExpression(this, XProperty).UpdateTarget();
        //BindingOperations.GetBindingExpression(Xbox, TextBox.TextProperty).UpdateTarget();
        //BindingOperations.GetBindingExpression(Xbox, XProperty).UpdateTarget();
        //Xbox.GetBindingExpression(TextBox.TextProperty).UpdateTarget();
        //GetBindingExpression(XProperty).UpdateTarget();
    }

I have tried several things - one at a time - (see below X=0.7;) to force the update to the TextBox Text but nothing has helped so far.

Thanks in advance.

laszlokiss88 · Accepted Answer · 2012-07-11 08:06:07Z

2

I'd write it in this way:

    public double X
    {
        get { return (double)GetValue(XProperty); }
        set { SetValue(XProperty, value); }
    }

    public static readonly DependencyProperty XProperty =
        DependencyProperty.Register("X", typeof(double), typeof(MainPage), new PropertyMetadata(new PropertyChangedCallback(Callback)));


    public static void Callback(DependencyObject o, DependencyPropertyChangedEventArgs e)
    {
        (o as MainPage).Xbox.Text = e.NewValue.ToString();
    }

    private void InsertCurrentBtnClick(object sender, RoutedEventArgs e)
    {
        X = 0.7;
    }

And the xaml code:

    <StackPanel Orientation="Horizontal" >
        <TextBox Name="Xbox" Width="50"/>
        <Button Content="Current" Click="InsertCurrentBtnClick" />
    </StackPanel>

answered Jul 11, 2012 at 8:06

laszlokiss88

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Comments

MBen · Accepted Answer · 2012-07-11 08:13:27Z

1

You need to set the DataContext for you Control. As I see X defined in your control, you need to do this :

    public MyUserControl()
    {
        InitializeComponent();

        // add this line
        this.DataContext = this;
    }

answered Jul 11, 2012 at 8:13

MBen

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2 Comments

MBen Over a year ago

welcome. DataContext and DataBinding are made to work together :)

Caroline Over a year ago

Oops, it seems I assessed this answer quickly. If I use this, my X gets no longer populated as a dependency property. It doesn't get whatever value is passed to it with <MyUserControl X={Binding Value} />

laszlokiss88 · Accepted Answer · 2012-07-11 08:13:34Z

1

Although, you can bind it as well, just change the xaml:

<UserControl x:Class="SilverlightApplication1.MainPage"
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"
Name="myWidnow"
d:DesignHeight="300" d:DesignWidth="400">

<Grid x:Name="LayoutRoot" Background="White">
    <StackPanel Orientation="Horizontal" >
        <TextBox Name="Xbox" Width="50" Text="{Binding ElementName=myWidnow, Path=X}" />
        <Button Content="Current" Click="InsertCurrentBtnClick" />
    </StackPanel>
</Grid>

Notice that I've added the Name proeprty to the UserControl. In this case, you don't have to change anything in the code behid.

answered Jul 11, 2012 at 8:13

laszlokiss88

4,0793 gold badges22 silver badges26 bronze badges

2 Comments

Caroline Over a year ago

Oops, it seems I assessed this answer quickly. If I use this, my X gets no longer populated as a dependency property. It doesn't get whatever value is passed to it with <MyUserControl X={Binding Value} />

MBen Over a year ago

Well you need to implement Value also as a dependencyProperty or implement INotigyPropertyChanged. The one using your UserConyrol needs to use DataContext as well.

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