Access named item inside ItemTemplate

Question

I have the following scenario:

<Button Click="ClickHandler">Click Me</Button>
<TextBox x:Name="MyInputTextBox" />
<ItemsControl ItemsSource="{Binding}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <TextBox x:Name="MyRepeatTextBox" Text="{Binding}" />
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

If MyRepeatTextBox.Text == MyInputTextBox.Text I want to change the color of MyRepeatTextBox.Background to Green. If MyRepeatTextBox.Text is blank I want to change the color to red. How would I implement the button click handler?

Answer 1

Not sure a button event would be the best for this.

As DataTriggers are again not brought outside the WPF world, those are out. There's no IMultiValueConverter either. Behaviours are currently out, but there is a nice codeplex project for them. I would use that

public class MatchTextForegroundBehaviour : Behavior<TextBox>
{
    private TextBox _attachedElement;

    public static readonly DependencyProperty MatchForegroundProperty =
        DependencyProperty.Register("MatchForeground", typeof(Brush),
        typeof(MatchTextForegroundBehaviour),
        new PropertyMetadata(new SolidColorBrush(Colors.Green), OnMatchForegroundChanged));

    public static readonly DependencyProperty FallbackForegroundProperty =
        DependencyProperty.Register("FallbackForeground", typeof(Brush),
        typeof(MatchTextForegroundBehaviour),
        new PropertyMetadata(new SolidColorBrush(Colors.Black), OnFallbackForegroundChanged));

    public static readonly DependencyProperty TextToMatchProperty =
        DependencyProperty.Register("TextToMatch", typeof(string),
        typeof(MatchTextForegroundBehaviour),
        new PropertyMetadata(null, OnTextToMatchChanged));

    public Brush MatchForeground
    {
        get { return (Brush)GetValue(MatchForegroundProperty); }
        set { SetValue(MatchForegroundProperty, value); }
    }

    public Brush FallbackForeground
    {
        get { return (Brush)GetValue(FallbackForegroundProperty); }
        set { SetValue(FallbackForegroundProperty, value); }
    }

    public string TextToMatch
    {
        get { return (string)GetValue(TextToMatchProperty); }
        set { SetValue(TextToMatchProperty, value); }
    }

    /// <summary>
    /// Event when the behavior is attached to a element.
    /// </summary>
    protected override void OnAttached()
    {
        base.OnAttached();
        _attachedElement = AssociatedObject;
        if(_attachedElement != null)
            _attachedElement.TextChanged += (s,e) => ChangeForeground();
    }

    private static void OnMatchForegroundChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var behavior = (MatchTextForegroundBehaviour)d;

        behavior.ChangeForeground();
    }

    private static void OnTextToMatchChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var behavior = (MatchTextForegroundBehaviour)d;

        behavior.ChangeForeground();
    }

    private static void OnFallbackForegroundChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var behavior = (MatchTextForegroundBehaviour)d;

        behavior.ChangeForeground();
    }


    private void ChangeForeground()
    {
        if (_attachedElement == null) return;
        if (string.IsNullOrEmpty(TextToMatch)) return; // change foreground to red?

        if (_attachedElement.Text == TextToMatch)
        {
            _attachedElement.Foreground = MatchForeground;
        }
        else
        {
            _attachedElement.Foreground = FallbackForeground;
        }
    }
}

And the xaml

<TextBox x:Name="MyRepeatTextBox" Text="{Binding}" 
         TextToMatch="{Binding Text, ElementName=MyInputTextBox}"
         FallbackForeground="Black" MatchForeground="Green" />

If a button click event is really how you want to do this, you can try the following. I have not compiled this against WinRT, but I think everything used is in WinRT.

Use the following ExtensionMethod

internal static class TreeExtensions
{
    public static T GetChildElement<T>(this DependencyObject element) where T :FrameworkElement
    {
        if (element == null) return null;
        if(element.GetType() == typeof(T)) return (T)element;

        T childAsT = null;
        int count = VisualTreeHelper.GetChildrenCount(element);
        for (int i = 0; i < count; i++)
        {
            var child = VisualTreeHelper.GetChild(element, i);
            childAsT = child.GetChildElement<T>();
            if (childAsT != null) break;
        }
        return childAsT;
    }
}

Inside the button click event you would do the following (assuming you gave the ItemsControl a name of itemsControl:

        foreach (var item in itemsControl.Items)
        {
            var element = itemsControl.ItemContainerGenerator.ContainerFromItem(item);
            var textblock = element.GetChildElement<TextBlock>();
            if (textblock != null)
            {
                if (textblock.Text == MyInputTextBox.Text)
                    textblock.Foreground = new SolidColorBrush(Colors.Green);
                else
                    textblock.Foreground = new SolidColorBrush(Colors.Black);
            }
        }