ListSortDirectionIndicator.cs

using System.ComponentModel;

namespace MaterialDesignThemes.Wpf;

[TemplateVisualState(GroupName = DirectionGroupName, Name = NoneStateName)]
[TemplateVisualState(GroupName = DirectionGroupName, Name = AscendingStateName)]
[TemplateVisualState(GroupName = DirectionGroupName, Name = DescendingStateName)]
public class ListSortDirectionIndicator : Control
{
    public const string DirectionGroupName = "Direction";
    public const string NoneStateName = "None";
    public const string AscendingStateName = "Ascending";
    public const string DescendingStateName = "Descending";

    static ListSortDirectionIndicator()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(ListSortDirectionIndicator), new FrameworkPropertyMetadata(typeof(ListSortDirectionIndicator)));
    }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        GotoVisualState(true, ListSortDirection);
    }


    public static readonly DependencyProperty ListSortDirectionProperty = DependencyProperty.Register(
        nameof(ListSortDirection), typeof(ListSortDirection?), typeof(ListSortDirectionIndicator), new PropertyMetadata(default(ListSortDirection?), ListSortDirectionPropertyChangedCallback));

    private static void ListSortDirectionPropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        var indicator = (ListSortDirectionIndicator)dependencyObject;
        indicator.GotoVisualState(true, indicator.ListSortDirection);
        indicator.IsNeutral = !indicator.ListSortDirection.HasValue;
    }

    public ListSortDirection? ListSortDirection
    {
        get { return (ListSortDirection?)GetValue(ListSortDirectionProperty); }
        set { SetValue(ListSortDirectionProperty, value); }
    }

    private static readonly DependencyPropertyKey IsNeutralPropertyKey =
        DependencyProperty.RegisterReadOnly(
            "IsNeutral", typeof(bool), typeof(ListSortDirectionIndicator),
            new PropertyMetadata(true));

    public static readonly DependencyProperty IsNeutralProperty =
        IsNeutralPropertyKey.DependencyProperty;

    public bool IsNeutral
    {
        get { return (bool)GetValue(IsNeutralProperty); }
        private set { SetValue(IsNeutralPropertyKey, value); }
    }

    private void GotoVisualState(bool useTransitions, ListSortDirection? direction)
    {
        var stateName = direction.HasValue
            ? (direction.Value == System.ComponentModel.ListSortDirection.Ascending
                ? AscendingStateName
                : DescendingStateName)
            : NoneStateName;

        VisualStateManager.GoToState(this, stateName, useTransitions);
    }
}