DataTemplateSelector get parent ActualWidth

Question

I am trying to set different DataTemplates to a ListBox depending on the Pages ActualWidth. In essence I would like to display more data to fill up the empty space.

Since the Item it self defines also is a parameter on what DataTemplate to use I figure I the best way is to use a DataTemplateSelector.

What would be the best way to achieve this since I have found no way of adding a DependencyProperty to a DataTemplateSelector.

Answer 1

When using a DataTemplateSelector, you get access to the data item that will have the DataTemplate applied to it. From the DataTemplateSelector page on MSDN:

public class TaskListDataTemplateSelector : DataTemplateSelector
{
    public override DataTemplate
        SelectTemplate(object item, DependencyObject container)
    {
        FrameworkElement element = container as FrameworkElement;

        if (element != null && item != null && item is Task)
        {
            Task taskitem = item as Task;

            if (taskitem.Priority == 1)
                return
                    element.FindResource("importantTaskTemplate") as DataTemplate;
            else 
                return
                    element.FindResource("myTaskTemplate") as DataTemplate;
        }

        return null;
    }
}

Note how the object item input parameter is cast to the actual type of the item in the above example. Therefore, you can add a property to your data item class to hold the size information with which you can determine which DataTemplate to apply.