WPF 数据绑定 - “自定义类型描述符”示例

Posted 2023-02-23

【中文标题】WPF 数据绑定 - “自定义类型描述符”示例

【英文标题】：WPF Data Binding - Example of "Custom Type Descriptor"

【发布时间】：2010-12-22 12:15:23

【问题描述】：

我看到有几个人说 WPF 可以将“自定义类型描述符”用于“更改通知”。

我知道如何进行更改通知的方法是：

object.GetBindingExpression(Bound.property).UpdateTarget();

或者让我的对象实现INotifiyPropertyChanged。

我看到 cmets 说自定义类型描述符也可以工作，但没有人给出一个很好的例子来说明它是如何工作的。我现在要求那个例子（IE 是 WPF 数据绑定和通过自定义类型描述符更新的一个很好的例子。）

【参考方案1】：

这是一个非常简单的例子。

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);
        
    

【参考方案2】：

我使用Kent Boogart 的出色且非常清晰的示例作为我的自定义类型的基础。

我认为应该对示例程序进行一些小改动，以阐明CustomTypeDescriptor 和PropertyDescriptor 之间的关系。

我认为数据应该存储在类型对象的实例上，而不是属性描述符上。 通常我希望每个自定义类型实例都保留它自己的属性描述符集合，而不是静态的。为了澄清这一点，我添加了更多信息（Type）来键入属性描述符。

第二点确实是域问题，但我希望更典型的使用需要实例属性数据，因为在编译时不知道属性时会使用这种类型。

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);
            
        
    

我希望我没有发出任何咆哮，因为这是我的第一篇文章！