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:
object.GetBindingExpression(Bound.property).UpdateTarget();
Or have my object implement INotifiyPropertyChanged.
I see comments saying that Custom Type Descriptors will work too, but no one gives a good example on how it works. I am now asking for that example (IE a good example of WPF Data Binding and updating via Custom Type Descriptors.)
Here's a pretty simple example for you.
Window1.xaml:
<Window x:Class="CTDExample.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<TextBlock>Name:</TextBlock>
<TextBox Grid.Column="1" Text="{Binding Name}"/>
<TextBlock Grid.Row="1">Age:</TextBlock>
<TextBox Grid.Row="1" Grid.Column="1" Text="{Binding Age}"/>
<TextBlock Grid.Row="2" Grid.ColumnSpan="2">
<TextBlock.Text>
<MultiBinding StringFormat="{}{0} is {1} years old.">
<Binding Path="Name"/>
<Binding Path="Age"/>
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</Grid>
</Window>
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<PropertyDescriptor> _propertyDescriptors = new List<PropertyDescriptor>();
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<object, object> _values;
public MyPropertyDescriptor(string name)
: base(name, null)
{
_values = new Dictionary<object, object>();
}
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);
}
}
}
I used the excellent and very clear example by Kent Boogart as the basis for my custom types.
I have a few minor changes I think should be made to the example program to clarify the relationship between the CustomTypeDescriptor and the PropertyDescriptor.
Type) to type property descriptor.The second point is really a domain issue, but I would expect a more typical use would require instance property data, as one uses such a type when the properties are not known at compile time.
MainWindow.xaml
<Window
x:Class="CTDExample.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<TextBlock>Name:</TextBlock>
<TextBox Grid.Column="1" Text="{Binding Name}"/>
<TextBlock Grid.Row="1">Age:</TextBlock>
<TextBox Grid.Row="1" Grid.Column="1" Text="{Binding Age}"/>
<TextBlock Grid.Row="2" Grid.ColumnSpan="2">
<TextBlock.Text>
<MultiBinding StringFormat="{}{0} is {1} years old.">
<Binding Path="Name"/>
<Binding Path="Age"/>
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</Grid>
</Window>
MainWindow.xaml.cs
using System.Windows;
namespace CTDExample
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var ctd = new MyCustomType();
ctd.AddProperty("Name", typeof(string)); // Now takes a Type argument.
ctd.AddProperty("Age", typeof(int));
DataContext = ctd;
}
}
}
MyCustomType.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
namespace CTDExample
{
public class MyCustomType : CustomTypeDescriptor
{
// This is instance data.
private readonly ICollection<PropertyDescriptor> _propertyDescriptors = new List<PropertyDescriptor>();
// The data is stored on the type instance.
private readonly IDictionary<string, object> _propertyValues = new Dictionary<string, object>();
// The property descriptor now takes an extra argument.
public void AddProperty(string name, Type type)
{
_propertyDescriptors.Add(new MyPropertyDescriptor(name, type));
}
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;
}
private class MyPropertyDescriptor : PropertyDescriptor
{
// This data is here to indicate that different instances of the type
// object may have properties of the same name, but with different
// characteristics.
private readonly Type _type;
public MyPropertyDescriptor(string name, Type type)
: base(name, null)
{
_type = type;
}
public override bool CanResetValue(object component)
{
throw new NotImplementedException();
}
public override Type ComponentType
{
get { throw new NotImplementedException(); }
}
public override object GetValue(object component)
{
MyCustomType obj = (MyCustomType)component;
object value = null;
obj._propertyValues.TryGetValue(Name, out value);
return value;
}
public override bool IsReadOnly
{
get { return false; }
}
public override Type PropertyType
{
get { return _type; }
}
public override void ResetValue(object component)
{
throw new NotImplementedException();
}
public override void SetValue(object component, object value)
{
var oldValue = GetValue(component);
if (oldValue != value)
{
MyCustomType obj = (MyCustomType)component;
obj._propertyValues[Name] = value;
OnValueChanged(component, new PropertyChangedEventArgs(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);
}
}
}
}
I hope I haven't made any howlers, as this is my first post!
