WPF Data Binding - Example of “Custom Type Descriptor”

Question

I see several people saying that WPF can use \"Custom Type Descriptors\" for \"Change notification\".

The ways I know how to do Change Notification are:

Answer 1

Here's a pretty simple example for you.

Window1.xaml:

    
        
            
            
        
        
            
            
            
        

        Name:
        

        Age:
        

        
            
                
                    
                    
                
            
        
    

Window1.xaml.cs:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows;

namespace CTDExample
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            var ctd = new CTD();
            ctd.AddProperty("Name");
            ctd.AddProperty("Age");
            DataContext = ctd;
        }
    }

    public class CTD : CustomTypeDescriptor
    {
        private static readonly ICollection _propertyDescriptors = new List();

        public void AddProperty(string name)
        {
            _propertyDescriptors.Add(new MyPropertyDescriptor(name));
        }

        public override PropertyDescriptorCollection GetProperties()
        {
            return new PropertyDescriptorCollection(_propertyDescriptors.ToArray());
        }

        public override PropertyDescriptorCollection GetProperties(Attribute[] attributes)
        {
            return GetProperties();
        }

        public override EventDescriptorCollection GetEvents()
        {
            return null;
        }

        public override EventDescriptorCollection GetEvents(Attribute[] attributes)
        {
            return null;
        }
    }

    public class MyPropertyDescriptor : PropertyDescriptor
    {
        private readonly IDictionary _values;

        public MyPropertyDescriptor(string name)
            : base(name, null)
        {
            _values = new Dictionary();
        }

        public override bool CanResetValue(object component)
        {
            throw new NotImplementedException();
        }

        public override Type ComponentType
        {
            get { throw new NotImplementedException(); }
        }

        public override object GetValue(object component)
        {
            object value = null;
            _values.TryGetValue(component, out value);
            return value;
        }

        public override bool IsReadOnly
        {
            get { return false; }
        }

        public override Type PropertyType
        {
            get { return typeof(object); }
        }

        public override void ResetValue(object component)
        {
            throw new NotImplementedException();
        }

        public override void SetValue(object component, object value)
        {
            var oldValue = GetValue(component);

            if (oldValue != value)
            {
                _values[component] = value;
                OnValueChanged(component, new PropertyChangedEventArgs(base.Name));
            }
        }

        public override bool ShouldSerializeValue(object component)
        {
            throw new NotImplementedException();
        }

        public override void AddValueChanged(object component, EventHandler handler)
        {
            // set a breakpoint here to see WPF attaching a value changed handler
            base.AddValueChanged(component, handler);
        }
    }
}