User Controls & Custom Controls

using System.Windows;
using System.Windows.Automation.Peers;
using System.Windows.Controls;
using System.Windows.Input;

namespace Bookshelf.Controls;

[TemplatePart(Name = PartSurface, Type = typeof(Border))]
[TemplatePart(Name = PartGlyphs, Type = typeof(TextBlock))]
public class StarRating : Control
{
    public const string PartSurface = "PART_Surface";
    public const string PartGlyphs = "PART_Glyphs";

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

    public static readonly DependencyProperty MaximumProperty = DependencyProperty.Register(
        nameof(Maximum), typeof(int), typeof(StarRating),
        new FrameworkPropertyMetadata(5, OnMaximumChanged), IsValidMaximum);

    public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
        nameof(Value), typeof(int), typeof(StarRating),
        new FrameworkPropertyMetadata(
            0,
            FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
            OnValueChanged,
            CoerceValue));

    public static readonly RoutedEvent ValueChangedEvent = EventManager.RegisterRoutedEvent(
        nameof(ValueChanged), RoutingStrategy.Bubble,
        typeof(RoutedPropertyChangedEventHandler<int>), typeof(StarRating));

    private Border? _surface;
    private TextBlock? _glyphs;

    public int Maximum
    {
        get => (int)GetValue(MaximumProperty);
        set => SetValue(MaximumProperty, value);
    }

    public int Value
    {
        get => (int)GetValue(ValueProperty);
        set => SetValue(ValueProperty, value);
    }

    public event RoutedPropertyChangedEventHandler<int> ValueChanged
    {
        add => AddHandler(ValueChangedEvent, value);
        remove => RemoveHandler(ValueChangedEvent, value);
    }

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

        if (_surface is not null)
        {
            _surface.MouseLeftButtonDown -= OnSurfaceMouseDown;
        }

        _surface = GetTemplateChild(PartSurface) as Border;
        _glyphs = GetTemplateChild(PartGlyphs) as TextBlock;

        if (_surface is not null)
        {
            _surface.MouseLeftButtonDown += OnSurfaceMouseDown;
        }

        UpdateGlyphs();
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        switch (e.Key)
        {
            case Key.Right or Key.Up:
                Value++;
                e.Handled = true;
                break;
            case Key.Left or Key.Down:
                Value--;
                e.Handled = true;
                break;
            case Key.Home:
                Value = 0;
                e.Handled = true;
                break;
            case Key.End:
                Value = Maximum;
                e.Handled = true;
                break;
            default:
                base.OnKeyDown(e);
                break;
        }
    }

    protected virtual void OnValueChanged(RoutedPropertyChangedEventArgs<int> args)
    {
        RaiseEvent(args);
    }

    protected override AutomationPeer OnCreateAutomationPeer() => new StarRatingAutomationPeer(this);

    private static bool IsValidMaximum(object value) => (int)value > 0;

    private static object CoerceValue(DependencyObject d, object baseValue)
    {
        var control = (StarRating)d;
        return Math.Clamp((int)baseValue, 0, control.Maximum);
    }

    private static void OnMaximumChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (StarRating)d;
        control.CoerceValue(ValueProperty);
        control.UpdateGlyphs();
    }

    private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (StarRating)d;
        control.UpdateGlyphs();

        var args = new RoutedPropertyChangedEventArgs<int>((int)e.OldValue, (int)e.NewValue, ValueChangedEvent);
        control.OnValueChanged(args);

        if (UIElementAutomationPeer.FromElement(control) is StarRatingAutomationPeer peer)
        {
            peer.RaiseValueChanged((int)e.OldValue, (int)e.NewValue);
        }
    }

    private void OnSurfaceMouseDown(object sender, MouseButtonEventArgs e)
    {
        if (_surface is null || _surface.ActualWidth <= 0)
        {
            return;
        }

        Focus();
        var fraction = e.GetPosition(_surface).X / _surface.ActualWidth;
        Value = (int)Math.Ceiling(fraction * Maximum);
        e.Handled = true;
    }

    private void UpdateGlyphs()
    {
        if (_glyphs is null)
        {
            return;
        }

        _glyphs.Text = new string('★', Value) + new string('☆', Maximum - Value);
    }
}

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:Bookshelf.Controls">

    <Style TargetType="{x:Type local:StarRating}">
        <Setter Property="Focusable" Value="True" />
        <Setter Property="IsTabStop" Value="True" />
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
        <Setter Property="FontSize" Value="20" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:StarRating}">
                    <Border x:Name="PART_Surface"
                            Background="Transparent"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Padding="{TemplateBinding Padding}">
                        <TextBlock x:Name="PART_Glyphs"
                                   Foreground="{TemplateBinding Foreground}"
                                   FontSize="{TemplateBinding FontSize}" />
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsKeyboardFocused" Value="True">
                            <Setter TargetName="PART_Surface" Property="BorderBrush"
                                    Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
                            <Setter TargetName="PART_Surface" Property="BorderThickness" Value="1" />
                        </Trigger>
                        <Trigger Property="IsEnabled" Value="False">
                            <Setter Property="Opacity" Value="0.5" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

using System.Windows;

[assembly: ThemeInfo(
    ResourceDictionaryLocation.None,
    ResourceDictionaryLocation.SourceAssembly)]

<StackPanel Margin="16" xmlns:ctl="clr-namespace:Bookshelf.Controls;assembly=Bookshelf.Controls">
    <TextBlock Text="Your rating" />
    <ctl:StarRating Maximum="5"
                    Value="{Binding SelectedBook.Rating, Mode=TwoWay}"
                    ValueChanged="OnRatingChanged"
                    AutomationProperties.Name="Book rating" />
</StackPanel>

<ListBox ItemsSource="{Binding Books}"
         ctl:StarRating.ValueChanged="OnAnyRatingChanged" />

<Style x:Key="BookRatingCircles" TargetType="ctl:StarRating">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ctl:StarRating">
                <Border x:Name="PART_Surface" Background="Transparent" Padding="2">
                    <TextBlock x:Name="PART_Glyphs" FontFamily="Segoe UI Symbol"
                               Foreground="{TemplateBinding Foreground}" />
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>