harmonia/Harmonia.WinUI/Views/PlaylistsView.xaml.cs

using CommunityToolkit.WinUI;
using Harmonia.WinUI.ViewModels;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using System.ComponentModel;

namespace Harmonia.WinUI.Views;

public sealed partial class PlaylistsView : UserControl
{
    private readonly PlaylistsViewModel _viewModel;

    public PlaylistsView()
    {
        InitializeComponent();

        _viewModel = (PlaylistsViewModel)DataContext;
        _viewModel.PropertyChanging += OnViewModelPropertyChanging;
        _viewModel.PropertyChanged += OnViewModelPropertyChanged;
    }

    private void OnViewModelPropertyChanging(object? sender, PropertyChangingEventArgs e)
    {
        switch (e.PropertyName)
        {
            case nameof(_viewModel.ActivePlaylist):
                UpdateListViewItemStyle(PlaylistItemStyle.Normal);
                break;
        }
    }

    private void OnViewModelPropertyChanged(object? sender, PropertyChangedEventArgs e)
    {
        switch (e.PropertyName)
        {
            case nameof(_viewModel.ActivePlaylist):
                UpdateListViewItemStyle(PlaylistItemStyle.Selected);
                break;
        }
    }

    private void UpdateListViewItemStyle(PlaylistItemStyle style)
    {
        ListViewItem listViewItem = (ListViewItem)PlaylistsListView.ContainerFromItem(_viewModel.ActivePlaylist);

        if (listViewItem is null)
            return;

        FrameworkElement? frameworkElement = TryGetFrameworkElement(listViewItem, "PlaylistListViewItem");

        if (frameworkElement == null)
            return;

        string playlistItemIconBrushName = style == PlaylistItemStyle.Selected ? "SelectedPlaylistIconPath" : "PlaylistIconPath";
        string playlistItemTitleBrushName = style == PlaylistItemStyle.Selected ? "SelectedPlaylistTitleTextBlock" : "PlaylistTitleTextBlock";
        string playlistItemSubtitleBrushName = style == PlaylistItemStyle.Selected ? "SelectedPlaylistSubtitleTextBlock" : "PlaylistSubtitleTextBlock";

        UpdateElementStyle(frameworkElement, "MusicNoteListPathIcon", playlistItemIconBrushName);
        UpdateElementStyle(frameworkElement, "PlaylistTitleTextBlock", playlistItemTitleBrushName);
        UpdateElementStyle(frameworkElement, "PlaylistSubtitleTextBlock", playlistItemSubtitleBrushName);
    }

    private static FrameworkElement? TryGetFrameworkElement(ListViewItem listViewItem, string elementName)
    {
        if (listViewItem.Name == elementName)
        {
            return listViewItem;
        }
        else
        {
            if (listViewItem.FindDescendant(elementName) is not FrameworkElement frameworkElement)
                return null;

            return frameworkElement;
        }
    }

    private void UpdateElementStyle(FrameworkElement dependencyObject, string elementName, string resourceName)
    {
        if (dependencyObject.FindDescendant(elementName) is not FrameworkElement frameworkElement)
            return;

        Resources.TryGetValue(resourceName, out object? resource);

        if (resource == null)
            Application.Current.Resources.TryGetValue(resourceName, out resource);

        if (resource is not Style style)
            return;

        frameworkElement.Style = style;
    }
}

public enum PlaylistItemStyle
{
    Normal,
    Selected
}