WPF_Practice/PacticeSolution/DependencyProperty/MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace DependencyPropertySample
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        // Dependency Property
        public static readonly DependencyProperty MyProperty = DependencyProperty.Register(nameof(MyFruit), typeof(string), typeof(MainWindow), new FrameworkPropertyMetadata(new PropertyChangedCallback(OnMyPropertyChanged)));

        public MainWindow()
        {
            InitializeComponent();
        }

        public string MyFruit
        {
            get { return (string)GetValue(MyProperty); }
            set { SetValue(MyProperty, value); }
        }

        public static void OnMyPropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            MainWindow win = o as MainWindow;
            if (win == null)
                return;

            win.Title = (e.OldValue == null) ? "Not selected" : $"Old value is {e.OldValue.ToString()}";
            win.txtFruit.Text = e.NewValue.ToString();
        }

        private void cboMain_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            ComboBox cb = sender as ComboBox;
            if (cb == null)
                return;

            ComboBoxItem item = cb.SelectedItem as ComboBoxItem;
            if (item == null) 
                return;

            MyFruit = item.Content.ToString();
        }
    }
}