wpf force to build visual tree

Question

I have ItemsControl with Grid as ItemsPanelTemplate

<ItemsControl ItemsSource="{Binding CellCollection}" Name="CellGrid">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Grid Name="grid" />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
</ItemsControl>

I create some UserControl with this ItemControl inside in code-behind, and then i need to create RowDefinitions and ColumnDefinitons. I use this method to get "grid":

private TChildItem FindVisualChild<TChildItem>(DependencyObject obj) where TChildItem : DependencyObject
    {
        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
        {
            var child = VisualTreeHelper.GetChild(obj, i);

            if (child != null && child is TChildItem)
                return (TChildItem)child;

            var childOfChild = FindVisualChild<TChildItem>(child);

            if (childOfChild != null)
                return childOfChild;
        }

        return null;
    }

But if i call this method before showing UserControl it returns null, so I cant find access "grid" and when UserControl appears it displayed not as I expected.

I tried to google but all i found is assumption that VisualTree not building for ItemControl until it showed on form.

Any suggestions? Thanks and sorry for bad english ;)

Mediacy

Answer 1

You can make a call to ApplyTemplate this tells the element to apply the template and build the visual tree.

Although, this doesn't apply templates all the way down. In this case you would first have to call ApplyTemplate() on the ItemsControl, then var item_presenter = FindVisualChild<ItemsPresenter>(items_control), then you have to call item_presenter.ApplyTemplate() and now you will have forced the Grid into the VisualTree.

Kareykari

hm, nope, not working, FindVisualChild() still returns null. Helps only showing UseControl and only then updating Row and Column Definitions – Mediacy

At which stage are you calling FindVisualChild? Construction, Loaded, something like that? – Kareykari

After creation UserControl I set DataContext, and FindVisualChild is calling when DataContextChanged event is raised – Mediacy

Just tried to update grid in Loaded event and it worked! Thanks for the tip – Mediacy