Behaviour of ItemsControl

Question

I have a screen with several UserControls, but only one of them remains active. The other UserControls aren't shown, but the user can switch the active flag of any of those who are not active. One of the UserControl contains an ItemsControl.

I need to know all the controls in the view, including those generated by an ItemsControl, after loading the first UserControl that is active in the screen, when view is finally initialized.

For ItemsControl, wpf didn't instance any item until it was painted on the screen that contains the UserControl (so I've tried, until the Load event is launched), so that I can't found the controls contained by the view because it didn't exist.

Is there any way to change this behavior?

I try to change the value of property VirtualizingStackPanel.IsVirtualizing to false, to avoid the previous behaviour, with no success. To illustrate this, I write this view example:

<Window x:Class="ContenidoEnTabs.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <StackPanel x:Name="spContainer" Orientation="Vertical" VirtualizingStackPanel.IsVirtualizing="False">
        <Button Content="Push" Click="Button_Click" />
    </StackPanel>
</Window>

This view creates a second control not visible until the user press the button:

public partial class MainWindow : Window
{
    private NotPaintedOnInitUserControl controlExtra;

    public MainWindow()
    {
        InitializeComponent();
        controlExtra = new NotPaintedOnInitUserControl();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        spContainer.Children.Add(controlExtra);
    }
}

The control not visible initially is as follow:

<UserControl x:Class="ContenidoEnTabs.NotPaintedOnInitUserControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d"
         d:DesignHeight="300" d:DesignWidth="300">
    <ItemsControl ItemsSource="{Binding MyCollection}" x:Name="itemsControlTarget" 
              VirtualizingStackPanel.IsVirtualizing="False">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <TextBox x:Name="aTextBox" Width="80" Initialized="ATextBox_Initialized" />
            </DataTemplate>
            </ItemsControl.ItemTemplate>
    </ItemsControl>
</UserControl>

and in CodeBehind I detect when the Items were created

public partial class NotPaintedOnInitUserControl : UserControl
{
    public NotPaintedOnInitUserControl()
    {
        InitializeComponent();
        DataContext = new SimpleListDataContext();
    }

    private void ATextBox_Initialized(object sender, EventArgs e)
    {
    }
}

And the DataContext used:

public class SimpleListDataContext
{
    private List<string> _myCollection;
    public List<string> MyCollection
    {
        get { return _myCollection ?? (_myCollection = new List<string> { "one", "two" }); }
        set { _myCollection = value; }
    }
}

Any ideas?

Thanks in advance.

Answer 1

If you want WPF to generate the tree for a control that isn't part of the view, you can "hydrate" and layout the control by forcing the layout to run. Something like this should work:

public partial class MainWindow : Window
{
    private NotPaintedOnInitUserControl controlExtra;

    public MainWindow()
    {
        InitializeComponent();

        controlExtra = new NotPaintedOnInitUserControl();

        // Force the control to render, even though it's not on the screen yet.
        var size = new Size(this.Width, this.Height);
        var rect = new Rect(new Point(0,0), size);
        controlExtra.Measure(size);
        controlExtra.Arrange(rect);
        controlExtra.InvalidateVisual();
        controlExtra.UpdateLayout();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        spContainer.Children.Add(controlExtra);
    }
}

Not sure if this is what you're asking. If not, please clarify paragraph 2.