How Can i add a "AddNew" button at the end of drop downs in a Custom ComboBox Control?

Question

I have a custom control with a ComboBox. I want to add a button at the end of the drop-down list that says "AddNew," such as "AddNewStudent," which, when clicked, opens a form to register a new student.

Since I expect to create many instances of the custom control, some of which may not need this feature, I want it to be activatable and vice versa. For instance, a ComboBox that lists students' grades doesn't need this feature because the grades are something known and unchanging. Additionally, I want the actions taken when the "AddNew" button is clicked to be a user-settable dependency property since the actions taken when the "AddNew" button is clicked will be different for each instance.

Here is the repos on github of the Example below .

customDateControl

Answer

Hi,
you can add Button, bind to ICommand property and add new student object.

XAML window:

And code:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Media;
using System.Linq;

namespace WpfApp131
{
	public class ViewModel : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;
		private void OnPropertyChanged([CallerMemberName] String propertyName = "")
			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

		// contructor: load StudentList 
		public ViewModel()
		{
			for (int i = 1; i <= 10; i++)
				_studentList.Add(new Student() { StudentId = i, StudentName = $"Student {i}" });
			_cvsStudentList.Source = _studentList;
		}

		internal ObservableCollection _studentList { get; set; } = new ObservableCollection();
		private CollectionViewSource _cvsStudentList = new CollectionViewSource();
		public ICollectionView StudentsView { get => _cvsStudentList.View; }
		public ObservableCollection BloodGroups { get; set; } = new ObservableCollection() { "A", "B", "AB", "0" };

		private Student _student;
		public Student Student
		{
			get => _student;
			set
			{
				_student = value;
				OnPropertyChanged();
				StudentsView.Refresh();
			}
		}
		public ICommand CmdNew
		{ get => new RelayCommand(CmdNewStudent); }
		private void CmdNewStudent(object obj)
		{
			int lastID = (from s in _studentList orderby s.StudentId descending select s.StudentId).FirstOrDefault();
			_studentList.Add(new Student() { StudentId = lastID + 1, StudentName = $"Student {lastID + 1}" });
			StudentsView.Refresh();
		}
	}
	public class Student : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;

		private void OnPropertyChanged([CallerMemberName] String propertyName = "") =>
			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

		public int StudentId { get; set; }

		private string _studentName;
		public string StudentName
		{
			get => _studentName;
			set
			{
				_studentName = value;
				OnPropertyChanged();
			}
		}

		private string _bloodgroup;
		public string BloodGroup
		{
			get => _bloodgroup;
			set
			{
				_bloodgroup = value;
				OnPropertyChanged();
			}
		}
	}
	public class FloatingLabelComboBox : Control, INotifyPropertyChanged
	{
		static FloatingLabelComboBox()
		{
			DefaultStyleKeyProperty.OverrideMetadata(typeof(FloatingLabelComboBox), new FrameworkPropertyMetadata(typeof(FloatingLabelComboBox)));
		}
		public FloatingLabelComboBox() => this.Loaded += FloatingLabelComboBox_Loaded;

		private void FloatingLabelComboBox_Loaded(object sender, RoutedEventArgs e)
		{
			Style st = new Style(typeof(ComboBoxItem));
			Binding b = new Binding() { Converter = CBConverter };
			st.Setters.Add(new Setter(ComboBoxItem.BackgroundProperty, b));
			if (CBConverter != null) this.Resources.Add(typeof(ComboBoxItem), st);
		}

		public static readonly DependencyProperty LabelTextProperty =
			 DependencyProperty.Register("LabelText", typeof(string),
				 typeof(FloatingLabelComboBox), new PropertyMetadata(string.Empty));
		public string LabelText
		{
			get { return GetValue(LabelTextProperty).ToString(); }
			set { SetValue(LabelTextProperty, value); }
		}

		public static readonly DependencyProperty LabelForegroundProperty =
				DependencyProperty.Register("LabelForeground", typeof(Brush),
					typeof(FloatingLabelComboBox), new PropertyMetadata(Brushes.AliceBlue));
		public Brush LabelForeground
		{
			get { return (Brush)GetValue(LabelForegroundProperty); }
			set { SetValue(LabelForegroundProperty, value); }
		}

		public static readonly DependencyProperty LabelFontSizeProperty =
				DependencyProperty.Register("LabelFontSize", typeof(double),
					typeof(FloatingLabelComboBox), new PropertyMetadata(10.0));
		public double LabelFontSize
		{
			get { return (double)GetValue(LabelFontSizeProperty); }
			set { SetValue(LabelFontSizeProperty, value); }
		}

		public static readonly DependencyProperty ItemsSourceProperty =
				DependencyProperty.Register("ItemsSource", typeof(object),
					typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public object ItemsSource
		{
			get { return GetValue(ItemsSourceProperty); }
			set { SetValue(ItemsSourceProperty, value); }
		}

		public static readonly DependencyProperty SelectedItemProperty =
				DependencyProperty.Register("SelectedItem", typeof(object),
					typeof(FloatingLabelComboBox),
						new FrameworkPropertyMetadata(null,
						FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
						OnSelectedItemChanged));
		public object SelectedItem
		{
			get { return GetValue(SelectedItemProperty); }
			set { SetValue(SelectedItemProperty, value); }
		}
		private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			FloatingLabelComboBox cc = d as FloatingLabelComboBox;
			cc.SelectedItem = e.NewValue;
			if (cc != null) cc.OnPropertyChanged(nameof(SelectedItem));
		}

		public static readonly DependencyProperty DisplayMemberPathProperty =
				DependencyProperty.Register("DisplayMemberPath", typeof(string),
					typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public string DisplayMemberPath
		{
			get { return GetValue(DisplayMemberPathProperty).ToString(); }
			set { SetValue(DisplayMemberPathProperty, value); }
		}

		public static readonly DependencyProperty SelectedValueProperty =
				DependencyProperty.RegisterAttached("SelectedValue", typeof(object),
					typeof(FloatingLabelComboBox),
						new FrameworkPropertyMetadata(null,
						FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
						new PropertyChangedCallback(OnSelectedValueChanged)));
		public object SelectedValue
		{
			get { return GetValue(SelectedValueProperty); }
			set { SetValue(SelectedValueProperty, value); }
		}
		private static void OnSelectedValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			FloatingLabelComboBox cc = d as FloatingLabelComboBox;
			cc.SelectedValue = e.NewValue;
			if (cc != null) cc.OnPropertyChanged(nameof(SelectedValue));
		}

		public static readonly DependencyProperty CBConverterProperty =
		DependencyProperty.Register("CBConverter", typeof(IValueConverter),
			typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public IValueConverter CBConverter
		{
			get { return (IValueConverter)GetValue(CBConverterProperty); }
			set { SetValue(CBConverterProperty, value); }
		}

		public static readonly DependencyProperty CommandProperty =
		DependencyProperty.RegisterAttached("Command", typeof(ICommand),
			typeof(FloatingLabelComboBox),
				new FrameworkPropertyMetadata(null));
		public object Command
		{
			get { return GetValue(CommandProperty); }
			set { SetValue(CommandProperty, value); }
		}
		public Visibility CommandVisible { get => (Command == null) ? Visibility.Collapsed : Visibility.Visible; }

		public event PropertyChangedEventHandler PropertyChanged;
		private void OnPropertyChanged([CallerMemberName] String propertyName = "")
			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
	}
	public class BoolToColorConverter : IValueConverter
	{
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
			Student st = value as Student;
			return (st != null && !string.IsNullOrEmpty(st.BloodGroup)) ? Brushes.LightGreen : Brushes.LightPink;
		}
		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			throw new NotImplementedException();
		}
	}
	public class RelayCommand : ICommand
	{
		private readonly Predicate

Answer

Hi,
to add New button at the end of drop downs you can use ID with value==0 and trigger like in following demo.

XAML:

Code:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Data;
using System.Windows.Input;

namespace WpfApp132
{
	public class ViewModel : INotifyPropertyChanged, ICommand
	{
		public event PropertyChangedEventHandler PropertyChanged;
		public event EventHandler CanExecuteChanged;

		private void OnPropertyChanged([CallerMemberName] String propertyName = "")
			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

		// contructor: load StudentList 
		public ViewModel()
		{
			for (int i = 1; i <= 10; i++)
				_studentList.Add(new Student() { StudentId = i, StudentName = $"Student {i}" });
			_studentList.Add(new Student() { StudentId = 0 });
			_cvsStudentList.Source = _studentList;
		}

		internal ObservableCollection _studentList { get; set; } = new ObservableCollection();
		private CollectionViewSource _cvsStudentList = new CollectionViewSource();
		public ICollectionView StudentsView { get => _cvsStudentList.View; }

		private Student _student;
		public Student Student
		{
			get => _student;
			set
			{
				_student = value;
				OnPropertyChanged();
				StudentsView.Refresh();
			}
		}
		public bool CanExecute(object parameter) => true;
		public void Execute(object parameter)
		{
			int lastID = (from s in _studentList orderby s.StudentId descending select s.StudentId).FirstOrDefault();
			Student buttonItem = (from s in _studentList where s.StudentId == 0 select s).FirstOrDefault(); ;
			_studentList.Remove(buttonItem);
			_studentList.Add(new Student() { StudentId = lastID + 1, StudentName = $"Student {lastID + 1}" });
			_studentList.Add(new Student() { StudentId = 0 }); 
			StudentsView.Refresh();
		}
	}
	public class Student 
	{
		public int StudentId { get; set; }
		public string StudentName { get; set; }
	}
}

Result:

Answer

Hi,
you can use Command property for switching "AddNew" like in following demo:

XAML:

Code:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Media;
using System.Linq;

namespace WpfApp133
{
	public class ViewModel : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;
		public event EventHandler CanExecuteChanged;

		private void OnPropertyChanged([CallerMemberName] String propertyName = "")
			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

		// contructor: load StudentList 
		public ViewModel()
		{
			for (int i = 1; i <= 10; i++)
				_studentList.Add(new Student() { StudentId = i, StudentName = $"Student {i}" });
		}

		internal ObservableCollection _studentList { get; set; } = new ObservableCollection();
		private CollectionViewSource _cvsStudentList = new CollectionViewSource();
		public ObservableCollection BloodGroups { get; set; } = new ObservableCollection() { "A", "B", "AB", "0" };

		public ICollectionView StudentsView
		{
			get
			{
				ObservableCollection _viewList = new ObservableCollection(_studentList);
				_viewList.Add(new Student() { StudentId = 0 });
				_cvsStudentList.Source = _viewList;
				return _cvsStudentList.View;
			}
		}

		private Student _student;
		public Student Student
		{
			get => _student;
			set
			{
				_student = value;
				OnPropertyChanged(nameof(StudentsView));
				OnPropertyChanged();
			}
		}

		public ICommand CmdNew
		{ get => new RelayCommand(CmdNewStudent); }
		private void CmdNewStudent(object obj)
		{
			int lastID = (from s in _studentList orderby s.StudentId descending select s.StudentId).FirstOrDefault();
			_studentList.Add(new Student() { StudentId = lastID + 1, StudentName = $"Student {lastID + 1}" });
			OnPropertyChanged(nameof(StudentsView));
		}
	}
	public class Student : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;

		private void OnPropertyChanged([CallerMemberName] String propertyName = "") =>
			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

		public int StudentId { get; set; }

		private string _studentName;
		public string StudentName
		{
			get => _studentName;
			set
			{
				_studentName = value;
				OnPropertyChanged();
			}
		}

		private string _bloodgroup;
		public string BloodGroup
		{
			get => _bloodgroup;
			set
			{
				_bloodgroup = value;
				OnPropertyChanged();
			}
		}
	}
	public class FloatingLabelComboBox : Control, INotifyPropertyChanged
	{
		static FloatingLabelComboBox()
		{
			DefaultStyleKeyProperty.OverrideMetadata(typeof(FloatingLabelComboBox), new FrameworkPropertyMetadata(typeof(FloatingLabelComboBox)));
		}
		public FloatingLabelComboBox() => this.Loaded += FloatingLabelComboBox_Loaded;

		private void FloatingLabelComboBox_Loaded(object sender, RoutedEventArgs e)
		{
			Style st = new Style(typeof(ComboBoxItem));
			Binding b = new Binding() { Converter = CBConverter };
			st.Setters.Add(new Setter(ComboBoxItem.BackgroundProperty, b));
			if (CBConverter != null) this.Resources.Add(typeof(ComboBoxItem), st);
		}

		public static readonly DependencyProperty LabelTextProperty =
			 DependencyProperty.Register("LabelText", typeof(string),
				 typeof(FloatingLabelComboBox), new PropertyMetadata(string.Empty));
		public string LabelText
		{
			get { return GetValue(LabelTextProperty).ToString(); }
			set { SetValue(LabelTextProperty, value); }
		}

		public static readonly DependencyProperty LabelForegroundProperty =
				DependencyProperty.Register("LabelForeground", typeof(Brush),
					typeof(FloatingLabelComboBox), new PropertyMetadata(Brushes.AliceBlue));
		public Brush LabelForeground
		{
			get { return (Brush)GetValue(LabelForegroundProperty); }
			set { SetValue(LabelForegroundProperty, value); }
		}

		public static readonly DependencyProperty LabelFontSizeProperty =
				DependencyProperty.Register("LabelFontSize", typeof(double),
					typeof(FloatingLabelComboBox), new PropertyMetadata(10.0));
		public double LabelFontSize
		{
			get { return (double)GetValue(LabelFontSizeProperty); }
			set { SetValue(LabelFontSizeProperty, value); }
		}

		public static readonly DependencyProperty ItemsSourceProperty =
				DependencyProperty.Register("ItemsSource", typeof(object),
					typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public object ItemsSource
		{
			get { return GetValue(ItemsSourceProperty); }
			set { SetValue(ItemsSourceProperty, value); }
		}

		public static readonly DependencyProperty SelectedItemProperty =
				DependencyProperty.Register("SelectedItem", typeof(object),
					typeof(FloatingLabelComboBox),
						new FrameworkPropertyMetadata(null,
						FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
						OnSelectedItemChanged));
		public object SelectedItem
		{
			get { return GetValue(SelectedItemProperty); }
			set { SetValue(SelectedItemProperty, value); }
		}
		private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			FloatingLabelComboBox cc = d as FloatingLabelComboBox;
			cc.SelectedItem = e.NewValue;
			if (cc != null) cc.OnPropertyChanged(nameof(SelectedItem));
		}

		public static readonly DependencyProperty DisplayMemberPathProperty =
				DependencyProperty.Register("DisplayMemberPath", typeof(string),
					typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public string DisplayMemberPath
		{
			get { return GetValue(DisplayMemberPathProperty).ToString(); }
			set { SetValue(DisplayMemberPathProperty, value); }
		}

		public static readonly DependencyProperty SelectedValueProperty =
				DependencyProperty.RegisterAttached("SelectedValue", typeof(object),
					typeof(FloatingLabelComboBox),
						new FrameworkPropertyMetadata(null,
						FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
						new PropertyChangedCallback(OnSelectedValueChanged)));
		public object SelectedValue
		{
			get { return GetValue(SelectedValueProperty); }
			set { SetValue(SelectedValueProperty, value); }
		}
		private static void OnSelectedValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			FloatingLabelComboBox cc = d as FloatingLabelComboBox;
			cc.SelectedValue = e.NewValue;
			if (cc != null) cc.OnPropertyChanged(nameof(SelectedValue));
		}

		public static readonly DependencyProperty CBConverterProperty =
		DependencyProperty.Register("CBConverter", typeof(IValueConverter),
			typeof(FloatingLabelComboBox), new PropertyMetadata(null));
		public IValueConverter CBConverter
		{
			get { return (IValueConverter)GetValue(CBConverterProperty); }
			set { SetValue(CBConverterProperty, value); }
		}

		public static readonly DependencyProperty CommandProperty =
		DependencyProperty.RegisterAttached("Command", typeof(ICommand),
			typeof(FloatingLabelComboBox),
				new FrameworkPropertyMetadata(null));
		public object Command
		{
			get { return GetValue(CommandProperty); }
			set { SetValue(CommandProperty, value); }
		}

		public static DependencyProperty
			PropertyPathProperty = DependencyProperty.Register("PropertyPath", typeof(string),
				typeof(FloatingLabelComboBox), null);
		public string PropertyPath
		{
			get { return GetValue(PropertyPathProperty).ToString(); }
			set { SetValue(PropertyPathProperty, value); }
		}
		public Visibility CommandVisible { get => (Command == null) ? Visibility.Collapsed : Visibility.Visible; }

		#region ItemTemplate
		private ComboBox myComboBox;
		public override void OnApplyTemplate()
		{
			base.OnApplyTemplate();
			//Find the combobox in the template once it's applied
			myComboBox = base.Template.FindName("PART_MyComboBox", this) as ComboBox;
			if (Command != null) ComboBoxItemTemplate();
		}

		private void ComboBoxItemTemplate()
		{
			//create the data template
			DataTemplate _dt = new DataTemplate();
			_dt.DataType = typeof(ComboBoxItem);

			//set up the grid
			FrameworkElementFactory _dtGrid = new FrameworkElementFactory(typeof(Grid));
			_dtGrid.Name = "myGrid";
			_dtGrid.SetValue(StackPanel.OrientationProperty, Orientation.Horizontal);

			//set up the textblock
			FrameworkElementFactory _dtTb = new FrameworkElementFactory(typeof(TextBlock));
			_dtTb.SetBinding(TextBlock.TextProperty, new Binding(DisplayMemberPath));
			_dtGrid.AppendChild(_dtTb);

			//set up the Button
			FrameworkElementFactory _dtBtn = new FrameworkElementFactory(typeof(Button));
			_dtBtn.Name = "cmdButton";
			_dtBtn.SetValue(Button.ContentProperty, "AddNew");
			_dtBtn.SetValue(Button.VisibilityProperty, Visibility.Collapsed);
			_dtBtn.SetValue(Button.CommandProperty, Command); ;
			_dtGrid.AppendChild(_dtBtn);

			//set up the trigger
			DataTrigger _dtTrigger = new DataTrigger() { Binding = new Binding("StudentId"), Value = 0 };
			_dtTrigger.Setters.Add(new Setter() { Property = Control.VisibilityProperty, Value = Visibility.Visible, TargetName = "cmdButton" });
			_dt.Triggers.Add(_dtTrigger);

			//set the visual tree of the data template
			_dt.VisualTree = _dtGrid;

			//set the item template to be our shiny new data template
			myComboBox.DisplayMemberPath = null;
			myComboBox.ItemTemplate = _dt;
		}
		#endregion

		public event PropertyChangedEventHandler PropertyChanged;
		private void OnPropertyChanged([CallerMemberName] String propertyName = "")
			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
	}
	public class BoolToColorConverter : IValueConverter
	{
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
			Student st = value as Student;
			return (st != null && !string.IsNullOrEmpty(st.BloodGroup)) ? Brushes.LightGreen : Brushes.LightPink;
		}
		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			throw new NotImplementedException();
		}
	}
	public class RelayCommand : ICommand
	{
		private readonly Predicate

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How Can i add a "AddNew" button at the end of drop downs in a Custom ComboBox Control?

3 answers