Wino-Mail/Wino.Mail/Controls/WinoExpander.cs

using CommunityToolkit.Diagnostics;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Hosting;
using Windows.UI.Xaml.Markup;

namespace Wino.Controls;

[ContentProperty(Name = nameof(Content))]
public partial class WinoExpander : Control
{
    private const string PART_HeaderGrid = "HeaderGrid";
    private const string PART_ContentAreaWrapper = "ContentAreaWrapper";
    private const string PART_ContentArea = "ContentArea";

    private ContentControl HeaderGrid;
    private ContentControl ContentArea;
    private Grid ContentAreaWrapper;

    public static readonly DependencyProperty HeaderProperty = DependencyProperty.Register(nameof(Header), typeof(UIElement), typeof(WinoExpander), new PropertyMetadata(null));
    public static readonly DependencyProperty ContentProperty = DependencyProperty.Register(nameof(Content), typeof(UIElement), typeof(WinoExpander), new PropertyMetadata(null));
    public static readonly DependencyProperty IsExpandedProperty = DependencyProperty.Register(nameof(IsExpanded), typeof(bool), typeof(WinoExpander), new PropertyMetadata(false, new PropertyChangedCallback(OnIsExpandedChanged)));
    public static readonly DependencyProperty TemplateSettingsProperty = DependencyProperty.Register(nameof(TemplateSettings), typeof(WinoExpanderTemplateSettings), typeof(WinoExpander), new PropertyMetadata(new WinoExpanderTemplateSettings()));

    public UIElement Content
    {
        get { return (UIElement)GetValue(ContentProperty); }
        set { SetValue(ContentProperty, value); }
    }

    public WinoExpanderTemplateSettings TemplateSettings
    {
        get { return (WinoExpanderTemplateSettings)GetValue(TemplateSettingsProperty); }
        set { SetValue(TemplateSettingsProperty, value); }
    }

    public bool IsExpanded
    {
        get { return (bool)GetValue(IsExpandedProperty); }
        set { SetValue(IsExpandedProperty, value); }
    }

    public UIElement Header
    {
        get { return (UIElement)GetValue(HeaderProperty); }
        set { SetValue(HeaderProperty, value); }
    }

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

        HeaderGrid = GetTemplateChild(PART_HeaderGrid) as ContentControl;
        ContentAreaWrapper = GetTemplateChild(PART_ContentAreaWrapper) as Grid;
        ContentArea = GetTemplateChild(PART_ContentArea) as ContentControl;

        Guard.IsNotNull(HeaderGrid, nameof(HeaderGrid));
        Guard.IsNotNull(ContentAreaWrapper, nameof(ContentAreaWrapper));
        Guard.IsNotNull(ContentArea, nameof(ContentArea));

        var clipComposition = ElementCompositionPreview.GetElementVisual(ContentAreaWrapper);
        clipComposition.Clip = clipComposition.Compositor.CreateInsetClip();

        ContentAreaWrapper.SizeChanged += ContentSizeChanged;
        HeaderGrid.Tapped += HeaderTapped;
    }

    private void ContentSizeChanged(object sender, SizeChangedEventArgs e)
    {
        TemplateSettings.ContentHeight = e.NewSize.Height;
        TemplateSettings.NegativeContentHeight = -1 * (double)e.NewSize.Height;
    }

    private void HeaderTapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        // Tapped is delegated from executing hover action like flag or delete.
        // No need to toggle the expander.

        if (Header is MailItemDisplayInformationControl itemDisplayInformationControl &&
            itemDisplayInformationControl.IsRunningHoverAction)
        {
            itemDisplayInformationControl.IsRunningHoverAction = false;
            return;
        }

        IsExpanded = !IsExpanded;
    }

    private static void OnIsExpandedChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        if (obj is WinoExpander control)
            control.UpdateVisualStates();
    }

    private void UpdateVisualStates()
    {
        VisualStateManager.GoToState(this, IsExpanded ? "Expanded" : "Collapsed", true);
    }
}

#region Settings

public class WinoExpanderTemplateSettings : DependencyObject
{
    public static readonly DependencyProperty HeaderHeightProperty = DependencyProperty.Register(nameof(HeaderHeight), typeof(double), typeof(WinoExpanderTemplateSettings), new PropertyMetadata(0.0));
    public static readonly DependencyProperty ContentHeightProperty = DependencyProperty.Register(nameof(ContentHeight), typeof(double), typeof(WinoExpanderTemplateSettings), new PropertyMetadata(0.0));
    public static readonly DependencyProperty NegativeContentHeightProperty = DependencyProperty.Register(nameof(NegativeContentHeight), typeof(double), typeof(WinoExpanderTemplateSettings), new PropertyMetadata(0.0));

    public double NegativeContentHeight
    {
        get { return (double)GetValue(NegativeContentHeightProperty); }
        set { SetValue(NegativeContentHeightProperty, value); }
    }

    public double HeaderHeight
    {
        get { return (double)GetValue(HeaderHeightProperty); }
        set { SetValue(HeaderHeightProperty, value); }
    }

    public double ContentHeight
    {
        get { return (double)GetValue(ContentHeightProperty); }
        set { SetValue(ContentHeightProperty, value); }
    }
}

#endregion