NestedStyleSelector implementation

[Art]

I hope that someone will find this as useful as it can be.

Purpose:

Can apply many StyleSelectors to one item by cascade.

public abstract class NestedStyleSelector : StyleSelector
{
    public StyleSelector ChildStyleSelector { get; set; }

    // Use this instead of the SelectStyle method
    //
    public abstract Style GetStyle(object item, DependencyObject container);

    public sealed override Style SelectStyle(object item, DependencyObject container)
    {
        Style currentStyle = GetStyle(item, container),
              childStyle = null;

        if (ChildStyleSelector != null)
        {
            childStyle = ChildStyleSelector.SelectStyle(item, container);
        }

        if (childStyle != null)
        {
            if (currentStyle != null && currentStyle.TargetType != childStyle.TargetType)
                throw new InvalidOperationException();

            var clonnedStyle = new Style(childStyle.TargetType)
            {
                BasedOn = currentStyle
            };

            foreach (var setterBase in childStyle.Setters)
            {
                var setter = setterBase as Setter;

                if (setter == null)
                    continue;

                clonnedStyle.Setters.Add(new Setter
                {
                    Property = setter.Property,
                    Value = setter.Value
                });
            }

            currentStyle = clonnedStyle;
        }

        return currentStyle ?? base.SelectStyle(item, container);
    }
}

 

Usage in child implementations:

<!-- Some class, that implements the NestedStyleSelector -->
<c:NestedStyleSelector>
    <c:NestedStyleSelector.ChildStyleSelector>
        <!-- Any another style selector -->
    </cNestedStyleSelector.ChildStyleSelector>
</c:NestedStyleSelector>

Restrictions:

- TargetType of all styles in chain must equals with it's parent returned style TargetType.

- Setter in choosen style of Child StyleSelector overrides the same property of parent style selector.

- BasedOn can be specified only in a first node declaration.

It works for me when I combine decisions, which row can be expanded and wich row has alternating background.

 

Sorry for my English :)

[Art]

There is strange issue, when setting currentStyle to childStyle (InvalidCastException). I've solved it by "clonning" the currentStyle too, before replacing it by childStyle:

public abstract class NestedStyleSelector : StyleSelector
{
    public StyleSelector ChildStyleSelector { get; set; }

    public abstract Style GetStyle(object item, DependencyObject container);

    public sealed override Style SelectStyle(object item, DependencyObject container)
    {
        Style currentStyle = CloneStyle(GetStyle(item, container)),
              childStyle = null;

        if (ChildStyleSelector != null)
        {
            childStyle = ChildStyleSelector.SelectStyle(item, container);
        }

        if (childStyle != null)
        {
            if (currentStyle != null && currentStyle.TargetType != childStyle.TargetType)
                throw new InvalidOperationException();

            childStyle = CloneStyle(childStyle);
            childStyle.BasedOn = currentStyle;

            currentStyle = childStyle;
        }

        return currentStyle ?? base.SelectStyle(item, container);
    }

    private static Style CloneStyle(Style sourceStyle)
    {
        if (sourceStyle == null)
            return null;

        var clonnedStyle = new Style(sourceStyle.TargetType)
        {
            BasedOn = sourceStyle.BasedOn
        };

        foreach (var setterBase in sourceStyle.Setters)
        {
            var setter = setterBase as Setter;

            if (setter == null)
                continue;

            clonnedStyle.Setters.Add(new Setter
            {
                Property = setter.Property,
                Value = setter.Value
            });
        }

        return clonnedStyle;
    }
}

[Stefan]

Hello Artur,

Thank you for sharing this solution with the community. I have updated your Telerik points as a gratitude for your contribution.

All the best,
Stefan X1
Telerik