delegates for FrameworkElementFactory

[trebahl]

The current template system is taylored for use in xaml and horribly cumbersome in a programmatic context.

How about adding to FrameworkElementFactory a constructor taking as argument a Func<object, FrameworkElement> , that would be called with the datacontext as argument when generating a control?

[trebahl]

It seems the datacontext is not available to the frameworkelementfactory. However, I think there is a simple workaround using selectors:

1. the user would pass a Func<FrameworkElement> to the factory, that could be stored in _knownTypeFactory, requiring no change to the type but the addition of a constructor.

2. for a control template, we can pass a delegate containing all the required information.

3. for a data template, we can couple this with a template selector to generate a new template for every data item, containing a delegate with the item in its closure.

[lindexi]

@trebahl I think FrameworkElementFactory is extremely difficult to write in the code and very cumbersome. But we can not replace the origin code with Func<FrameworkElement>, because the origin code will create the template.

[trebahl]

I think I got it working using reflection to assign _knownTypeFactory.

    public class DelegateTemplate
    {
        static readonly FieldInfo ktf = typeof(FrameworkElementFactory).GetField("_knownTypeFactory", BindingFlags.NonPublic | BindingFlags.Instance);
        public static TTemplate CreateTemplate<TTemplate>(Func<FrameworkElement> gen) where TTemplate : FrameworkTemplate, new()
        {
            var t = new TTemplate();
            var f = new FrameworkElementFactory(typeof(FrameworkElement));
            ktf.SetValue(f, new Func<object>(() => gen()));
            t.VisualTree = f;
            return t;
        }

        public static ControlTemplate ControlTemplate(Func<FrameworkElement> gen) => CreateTemplate<ControlTemplate>(gen);

        class Selector<TItem> : DataTemplateSelector
        {
            public Func<TItem, FrameworkElement> Gen;
            public override DataTemplate SelectTemplate(object item, DependencyObject container)
            {
                var gen = () => Gen((TItem)item);
                return CreateTemplate<DataTemplate>(gen);
            }
        }

        public static DataTemplateSelector DataTemplateSelector<TItem>(Func<TItem, FrameworkElement> gen) => new Selector<TItem>() { Gen = gen };
    }

Then installing a data template is as easy as ctrl.ItemTemplateSelector = DelegateTemplate.DataTemplateSelector<MyItemType>(it => code to generate a visual tree).