elwig/Elwig/Controls/CheckComboBox.cs

using System.Linq;
using System.Windows;
using System.Windows.Controls;

namespace Elwig.Controls {
    public class CheckComboBox : ListBox {

        public static readonly DependencyProperty DelimiterProperty = DependencyProperty.Register(nameof(Delimiter), typeof(string), typeof(CheckComboBox), new FrameworkPropertyMetadata(", "));
        public string Delimiter {
            get => (string)GetValue(DelimiterProperty);
            set => SetValue(DelimiterProperty, value);
        }

        public static readonly DependencyProperty AllItemsSelectedContentProperty = DependencyProperty.Register(nameof(AllItemsSelectedContent), typeof(string), typeof(CheckComboBox), new FrameworkPropertyMetadata("All"));
        public string AllItemsSelectedContent {
            get => (string)GetValue(AllItemsSelectedContentProperty);
            set => SetValue(AllItemsSelectedContentProperty, value);
        }

        public static readonly DependencyProperty IsSelectAllActiveProperty = DependencyProperty.Register(nameof(IsSelectAllActive), typeof(bool), typeof(CheckComboBox), new FrameworkPropertyMetadata(false));
        public bool IsSelectAllActive {
            get => (bool)GetValue(IsSelectAllActiveProperty);
            set => SetValue(IsSelectAllActiveProperty, value);
        }

        public static readonly DependencyProperty SelectAllContentProperty = DependencyProperty.Register(nameof(SelectAllContent), typeof(string), typeof(CheckComboBox), new FrameworkPropertyMetadata("All"));
        public string SelectAllContent {
            get => (string)GetValue(SelectAllContentProperty);
            set => SetValue(SelectAllContentProperty, value);
        }

        public static readonly DependencyProperty AllItemsSelectedProperty = DependencyProperty.Register(nameof(AllItemsSelected), typeof(bool?), typeof(CheckComboBox), new FrameworkPropertyMetadata(false));
        public bool? AllItemsSelected {
            get => (bool?)GetValue(AllItemsSelectedProperty);
            set => SetValue(AllItemsSelectedProperty, value);
        }

        public static readonly DependencyProperty IsDropDownOpenProperty = DependencyProperty.Register(nameof(IsDropDownOpen), typeof(bool), typeof(CheckComboBox), new FrameworkPropertyMetadata(false));
        public bool IsDropDownOpen {
            get => (bool)GetValue(IsDropDownOpenProperty);
            set => SetValue(IsDropDownOpenProperty, value);
        }

        public static readonly DependencyProperty MaxDropDownHeightProperty = DependencyProperty.Register(nameof(MaxDropDownHeight), typeof(double), typeof(CheckComboBox), new FrameworkPropertyMetadata(ComboBox.MaxDropDownHeightProperty.DefaultMetadata.DefaultValue));
        public double MaxDropDownHeight {
            get => (double)GetValue(MaxDropDownHeightProperty);
            set => SetValue(MaxDropDownHeightProperty, value);
        }

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

        private TextBlock TextBox;

        public CheckComboBox() {
            SelectionMode = SelectionMode.Multiple;
        }

        public override void OnApplyTemplate() {
            TextBox = (GetTemplateChild("TextBox") as TextBlock)!;
            var button = GetTemplateChild("Button") as Button;
            button!.Click += Button_MouseDown;
            var item = GetTemplateChild("SelectAllItem") as ListBoxItem;
            item!.PreviewMouseDown += SelectAllItem_MouseDown;
            SelectionChanged += OnSelectionChanged;
            IsEnabledChanged += OnIsEnabledChanged;
            base.OnApplyTemplate();
        }

        private void Button_MouseDown(object sender, RoutedEventArgs evt) {
            IsDropDownOpen = !IsDropDownOpen;
        }

        private void SelectAllItem_MouseDown(object sender, RoutedEventArgs evt) {
            if (AllItemsSelected == false) {
                SelectAll();
            } else {
                UnselectAll();
            }
            evt.Handled = true;
        }

        private void OnSelectionChanged(object sender, SelectionChangedEventArgs evt) {
            var dmp = DisplayMemberPath != null && DisplayMemberPath != "" ? DisplayMemberPath : null;
            if (SelectedItems.Count == ItemsSource.Cast<object>().Count() && AllItemsSelectedContent != null) {
                TextBox.Text = AllItemsSelectedContent;
                AllItemsSelected = true;
            } else if (SelectedItems.Count == 0) {
                TextBox.Text = "";
                AllItemsSelected = false;
            } else {
                TextBox.Text = string.Join(Delimiter,
                    dmp == null ? SelectedItems.Cast<object>() :
                    SelectedItems.Cast<object>()
                        .Select(i => i.GetType().GetProperty(dmp)?.GetValue(i))
                );
                AllItemsSelected = null;
            }
        }

        private void OnIsEnabledChanged(object sender, DependencyPropertyChangedEventArgs evt) {
            if (!IsEnabled) IsDropDownOpen = false;
        }
    }
}