System.Dynamic.ExpandoObject 类

项目
01/11/2024

本文提供了此 API 参考文档的补充说明。

通过 ExpandoObject 该类，你可以在运行时添加和删除其实例的成员，以及设置和获取这些成员的值。此类支持动态绑定，因此可以使用标准语法，例如 sampleObject.sampleMember ，而不是更复杂的 sampleObject.GetAttribute("sampleMember")语法。

该 ExpandoObject 类实现标准动态语言运行时（DLR）接口 IDynamicMetaObjectProvider，使你可以在支持 DLR 互操作性模型的语言之间共享类的 ExpandoObject 实例。例如，可以在 C# 中创建类的 ExpandoObject 实例，然后将其传递给 IronPython 函数。有关详细信息，请参阅动态语言运行时概述和 ExpandoObject 简介。

该 ExpandoObject 类是动态对象概念的实现，可实现获取、设置和调用成员。如果要定义具有其自己的动态调度语义的类型，请使用该 DynamicObject 类。如果要定义动态对象如何参与互操作性协议并管理 DLR 快速动态调度缓存，请创建自己的接口实现 IDynamicMetaObjectProvider 。

创建实例

在 C# 中，若要为类的ExpandoObject实例启用后期绑定，必须使用dynamic关键字 (keyword)。有关更多信息，请参见使用类型 dynamic。

在 Visual Basic 中，后期绑定支持动态操作。有关详细信息，请参阅早期绑定和后期绑定（Visual Basic）。

下面的代码示例演示如何创建类的 ExpandoObject 实例。

dynamic sampleObject = new ExpandoObject();

Dim sampleObject As Object = New ExpandoObject()

添加新成员

可以将属性、方法和事件添加到类的 ExpandoObject 实例。

下面的代码示例演示如何向类的 ExpandoObject 实例添加新属性。

sampleObject.test = "Dynamic Property";
Console.WriteLine(sampleObject.test);
Console.WriteLine(sampleObject.test.GetType());
// This code example produces the following output:
// Dynamic Property
// System.String

sampleObject.Test = "Dynamic Property"
Console.WriteLine(sampleObject.test)
Console.WriteLine(sampleObject.test.GetType())
' This code example produces the following output:
' Dynamic Property
' System.String

这些方法表示存储为委托的 lambda 表达式，这些表达式在需要时可以调用这些表达式。下面的代码示例演示如何添加递增动态属性值的方法。

sampleObject.number = 10;
sampleObject.Increment = (Action)(() => { sampleObject.number++; });

// Before calling the Increment method.
Console.WriteLine(sampleObject.number);

sampleObject.Increment();

// After calling the Increment method.
Console.WriteLine(sampleObject.number);
// This code example produces the following output:
// 10
// 11

sampleObject.Number = 10
sampleObject.Increment = Function() sampleObject.Number + 1
' Before calling the Increment method.
Console.WriteLine(sampleObject.number)

sampleObject.Increment.Invoke()

' After calling the Increment method.
Console.WriteLine(sampleObject.number)
' This code example produces the following output:
' 10
' 11

下面的代码示例演示如何将事件添加到类的 ExpandoObject 实例。

class Program
{
    static void Main(string[] args)
    {
        dynamic sampleObject = new ExpandoObject();

        // Create a new event and initialize it with null.
        sampleObject.sampleEvent = null;

        // Add an event handler.
        sampleObject.sampleEvent += new EventHandler(SampleHandler);

        // Raise an event for testing purposes.
        sampleObject.sampleEvent(sampleObject, new EventArgs());
   }

    // Event handler.
    static void SampleHandler(object sender, EventArgs e)
    {
        Console.WriteLine("SampleHandler for {0} event", sender);
    }
}
// This code example produces the following output:
// SampleHandler for System.Dynamic.ExpandoObject event.

Module Module1

Sub Main()
    Dim sampleObject As Object = New ExpandoObject()

    ' Create a new event and initialize it with null.
    sampleObject.sampleEvent = Nothing

    ' Add an event handler.
    Dim handler As EventHandler = AddressOf SampleHandler
    sampleObject.sampleEvent =
        [Delegate].Combine(sampleObject.sampleEvent, handler)

    ' Raise an event for testing purposes.
    sampleObject.sampleEvent.Invoke(sampleObject, New EventArgs())

End Sub

' Event handler.
Sub SampleHandler(ByVal sender As Object, ByVal e As EventArgs)
    Console.WriteLine("SampleHandler for {0} event", sender)
End Sub

' This code example produces the following output:
' SampleHandler for System.Dynamic.ExpandoObject event.

End Module

作为参数传递

可以将类的 ExpandoObject 实例作为参数传递。请注意，这些实例被视为 C# 中的动态对象和 Visual Basic 中的后期绑定对象。这意味着你没有对象成员的 IntelliSense，并且调用不存在的成员时不会收到编译器错误。如果调用不存在的成员，将发生异常。

下面的代码示例演示如何创建和使用方法打印属性的名称和值。

class Program
{
    static void Main(string[] args)
    {
        dynamic employee, manager;

        employee = new ExpandoObject();
        employee.Name = "John Smith";
        employee.Age = 33;

        manager = new ExpandoObject();
        manager.Name = "Allison Brown";
        manager.Age = 42;
        manager.TeamSize = 10;

        WritePerson(manager);
        WritePerson(employee);
    }
    private static void WritePerson(dynamic person)
    {
        Console.WriteLine("{0} is {1} years old.",
                          person.Name, person.Age);
        // The following statement causes an exception
        // if you pass the employee object.
        // Console.WriteLine("Manages {0} people", person.TeamSize);
    }
}
// This code example produces the following output:
// John Smith is 33 years old.
// Allison Brown is 42 years old.

Sub Main()
    Dim employee, manager As Object

    employee = New ExpandoObject()
    employee.Name = "John Smith"
    employee.Age = 33

    manager = New ExpandoObject()
    manager.Name = "Allison Brown"
    manager.Age = 42
    manager.TeamSize = 10

    WritePerson(manager)
    WritePerson(employee)
End Sub

Private Sub WritePerson(ByVal person As Object)

    Console.WriteLine("{0} is {1} years old.",
                      person.Name, person.Age)
    ' The following statement causes an exception
    ' if you pass the employee object.
    ' Console.WriteLine("Manages {0} people", person.TeamSize)

End Sub

枚举和删除成员

ExpandoObject 类实现 IDictionary<String, Object> 接口。这样就可以在运行时枚举添加到类实例 ExpandoObject 的成员。如果在编译时不知道实例可能具有的成员，这可能很有用。

下面的代码示例演示如何将类IDictionary<TKey,TValue>的ExpandoObject实例强制转换为接口并枚举实例的成员。

dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;

foreach (var property in (IDictionary<String, Object>)employee)
{
    Console.WriteLine(property.Key + ": " + property.Value);
}
// This code example produces the following output:
// Name: John Smith
// Age: 33

Dim employee As Object = New ExpandoObject()
employee.Name = "John Smith"
employee.Age = 33
For Each member In CType(employee, IDictionary(Of String, Object))
    Console.WriteLine(member.Key & ": " & member.Value)
Next
' This code example produces the following output:
' Name: John Smith
' Age: 33

在不使用语法删除成员（如 C# 和 Visual Basic）的语言中，可以通过隐式将接口的ExpandoObjectIDictionary<String, Object>实例强制转换为接口，然后将成员删除为键/值对来删除成员。这在下面的示例中显示。

dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
((IDictionary<String, Object>)employee).Remove("Name");

Dim employee As Object = New ExpandoObject()
employee.Name = "John Smith"
CType(employee, IDictionary(Of String, Object)).Remove("Name")

接收属性更改通知

该 ExpandoObject 类实现接口， INotifyPropertyChanged 并在添加、删除或修改成员时引发 PropertyChanged 事件。这使类能够 ExpandoObject 与 Windows Presentation Foundation （WPF）数据绑定和其他环境集成，这些环境需要通知对象内容中的更改。

下面的代码示例演示如何为 PropertyChanged 事件创建事件处理程序。

// Add "using System.ComponentModel;" line
// to the beginning of the file.
class Program
{
    static void Test()
    {
        dynamic employee = new ExpandoObject();
        ((INotifyPropertyChanged)employee).PropertyChanged +=
            new PropertyChangedEventHandler(HandlePropertyChanges);
        employee.Name = "John Smith";
    }

    private static void HandlePropertyChanges(
        object sender, PropertyChangedEventArgs e)
    {
        Console.WriteLine("{0} has changed.", e.PropertyName);
    }
}

' Add "Imports System.ComponentModel" line 
' to the beginning of the file.
Sub Main()
    Dim employee As Object = New ExpandoObject
    AddHandler CType(
        employee, INotifyPropertyChanged).PropertyChanged,
        AddressOf HandlePropertyChanges
    employee.Name = "John Smith"
End Sub

Private Sub HandlePropertyChanges(
       ByVal sender As Object, ByVal e As PropertyChangedEventArgs)
    Console.WriteLine("{0} has changed.", e.PropertyName)
End Sub

通过