Question

I’m trying to build a set of typical CRUD maintenance forms in WPF – that are going to be pretty much the same except that they work on different database records.

Rather than creating a new window class for each, I’m trying to use a single window class that instantiated with a different ViewModel class for each database table, and for which I have a different UserControl defined for each ViewModel.

So, if I instantiate the window with its DataContext set to an instance of Record1ViewModel, I want to display it in the window using a Record1UserControl, if it’s set to an instance of Record2ViewModel, I want to display it using a Record2UserControl.

I’ve verified that both user controls work fine, by defining them each directly in the window’s XAML. But I’ve not figured out how to select one or the other, based on the type of the ViewModel.

This is not working:

<myWindow.Resources>

    <DataTemplate x:Key="{x:Type ViewModels:Record1ViewModel}">
        <MaintenanceControls:Record1 />
    </DataTemplate>
    <DataTemplate x:Key="{x:Type ViewModels:Record2ViewModel}">
        <MaintenanceControls:Record1 />
    </DataTemplate>

</myWindow.Resources>

<ContentPresenter Content="{Binding}" />

What I get, in the ContentPresenter, is the name of the type. The DataTemplates are not used.

Any ideas?

Answer 1

You can use the DataTemplateSelector to dynamically select a DataTemplate at run time something along the lines of

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;
        }
    }