DynamicObject Class (System.Dynamic)

Switch View

Collapse All

.NET Framework Class Library

DynamicObject Class

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

Provides a base class for specifying dynamic behavior at run time. This class must be inherited; you cannot instantiate it directly.

Namespace: System.Dynamic
Assembly: System.Core (in System.Core.dll)

Syntax

Visual Basic (Declaration)

Public Class DynamicObject _
    Implements IDynamicMetaObjectProvider

Visual Basic (Usage)

Dim instance As DynamicObject

public class DynamicObject : IDynamicMetaObjectProvider

Visual C++

public ref class DynamicObject : IDynamicMetaObjectProvider

type DynamicObject =  
    class
        interface IDynamicMetaObjectProvider
    end

Remarks

The DynamicObject class enables you to define which operations can be performed on dynamic objects and how to perform those operations. For example, you can define what happens when you try to get or set an object property, call a method, or perform standard mathematical operations such as addition and multiplication.

This class can be useful if you want to create a more convenient protocol for a library. For example, if users of your library have to use syntax like Scriptobj.SetProperty("Count", 1), you can provide the ability to use much simpler syntax, like scriptobj.Count = 1.

You cannot directly create an instance of the DynamicObject class. To implement the dynamic behavior, you may want to inherit the DynamicObject class and override necessary methods. For example, if you need only operations for setting and getting properties, you can override just the TrySetMember and TryGetMember methods.

You can also add your own members to classes derived from the DynamicObject class. For example, if you override the TrySetMember method, the dynamic dispatch system first tries to determine whether the specified property exists in the class. If it does not find the property, it uses the TrySetMember implementation.

In C#, to create instances of classes derived from the DynamicObject class, you must use the dynamic keyword. For more information, see Using Type dynamic (C# Programming Guide).

In Visual Basic, dynamic operations are supported by late binding. For more information, see Early and Late Binding.

The following code example demonstrates how to create an instance of a class that is derived from the DynamicObject class.

public class SampleDynamicObject : DynamicObject {}
//...
dynamic sampleObject = new SampleDynamicObject ();

Visual Basic

Public Class SampleDynamicObject 
    Inherits DynamicObject
'...
Dim sampleObject As Object = New SampleDynamicObject()

The DynamicObject class implements the standard dynamic language runtime (DLR) interface IDynamicMetaObjectProvider, which enables you to share instances of the DynamicObject class between languages that support the DLR interoperability model. For example, you can create an instance of the DynamicObject class in C# and then pass it to an IronPython function. For more information, see Dynamic Language Runtime Overview and documentation on the CodePlex Web site.

Note
If you have a simple scenario in which you need an object that can only add and remove members at run time but that does not need to define operation specifics, use the ExpandoObject class. If you have a more advanced scenario in which you need to define how dynamic objects participate in the interoperability protocol, or you need to manage DLR fast dynamic dispatch caching, create your own implementation of the IDynamicMetaObjectProvider interface.

Note

If you have a simple scenario in which you need an object that can only add and remove members at run time but that does not need to define operation specifics, use the ExpandoObject class.

If you have a more advanced scenario in which you need to define how dynamic objects participate in the interoperability protocol, or you need to manage DLR fast dynamic dispatch caching, create your own implementation of the IDynamicMetaObjectProvider interface.

Examples

Assume that you want to provide alternative syntax for accessing values in a dictionary, so that instead of writing sampleDictionary["Text"] = "Sample text" (sampleDictionary("Text") = "Sample text" in Visual Basic), you can write sampleDictionary.Text = "Sample text". Also, this syntax must be case-insensitive, so that sampleDictionary.Text is equivalent to sampleDictionary.text.

The following code example demonstrates the DynamicDictionary class, which is derived from the DynamicObject class. The DynamicDictionary class contains an object of the Dictionary<string, object> type (Dictionary(Of String, Object) in Visual Basic) to store the key-value pairs, and overrides the TrySetMember and TryGetMember methods to support the new syntax. It also provides a Count property, which shows how many dynamic properties the dictionary contains.

using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq.Expressions;

// The class derived from DynamicObject.
public class DynamicDictionary : DynamicObject
{
    // The inner dictionary.
    Dictionary<string, object> dictionary
        = new Dictionary<string, object>();

    // This property returns the number of elements
    // in the inner dictionary.
    public int Count
    {
        get
        {
            return dictionary.Count;
        }
    }    
    
    // If you try to get a value of a property 
    // not defined in the class, this method is called.
    public override bool TryGetMember(
        GetMemberBinder binder, out object result)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        string name = binder.Name.ToLower();

        // If the property name is found in a dictionary,
        // set the result parameter to the property value and return true.
        // Otherwise, return false.
        return dictionary.TryGetValue(binder.Name, out result);
    }

    // If you try to set a value of a property that is
    // not defined in the class, this method is called.
    public override bool TrySetMember(
        SetMemberBinder binder, object value)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        dictionary[binder.Name.ToLower()] = value;

        // You can always add a value to a dictionary,
        // so this method always returns true.
        return true;
    }
    
}

class Program
{
    static void Main(string[] args)
    {
        // Creating a dynamic dictionary.
        dynamic person = new DynamicDictionary();

        // Adding new dynamic properties. 
        // The TrySetMember method is called.
        person.FirstName = "Ellen";
        person.LastName = "Adams";

        // Getting values of the dynamic properties.
        // The TryGetMember method is called.
        // Note that property names are case-insensitive.
        Console.WriteLine(person.firstname + " " + person.lastname);

        // Getting the value of the Count property.
        // The TryGetMember is not called, 
        // because the property is defined in the class.
        Console.WriteLine(
            "Number of dynamic properties:" + person.Count);

        // The following statement throws an exception at run time.
        // There is no "address" property,
        // so the TryGetMember method returns false and this causes a
        // RuntimeBinderException.
        // Console.WriteLine(person.address);
    }    
}

// This example has the following output:
// Ellen Adams
// Number of dynamic properties: 2

Visual Basic

Imports System.Dynamic

' The class derived from DynamicObject.
Public Class DynamicDictionary
    Inherits DynamicObject

    ' The inner dictionary.
    Dim dictionary As New Dictionary(Of String, Object)

    ' This property returns the number of elements
    ' in the inner dictionary.
    ReadOnly Property Count As Integer
        Get
            Return dictionary.Count
        End Get
    End Property


    ' If you try to get a value of a property that is
    ' not defined in the class, this method is called.

    Public Overrides Function TryGetMember(
        ByVal binder As System.Dynamic.GetMemberBinder,
        ByRef result As Object) As Boolean

        ' Converting the property name to lowercase
        ' so that property names become case-insensitive.
        Dim name As String = binder.Name.ToLower()

        ' If the property name is found in a dictionary,
        ' set the result parameter to the property value and return true.
        ' Otherwise, return false.
        Return dictionary.TryGetValue(binder.Name, result)
    End Function

    Public Overrides Function TrySetMember(
        ByVal binder As System.Dynamic.SetMemberBinder, 
        ByVal value As Object) As Boolean

        ' Converting the property name to lowercase
        ' so that property names become case-insensitive.
        dictionary(binder.Name.ToLower()) = value

        ' You can always add a value to a dictionary,
        ' so this method always returns true.
        Return True
    End Function
End Class

Module Module1
    Sub Main()
        ' Creating a dynamic dictionary.
        Dim person As Object = New DynamicDictionary()

        ' Adding new dynamic properties.
        ' The TrySetMember method is called.
        person.FirstName = "Ellen"
        person.LastName = "Adams"

        ' Getting values of the dynamic properties.
        ' The TryGetMember method is called.
        ' Note that property names are now case-insensitive,
        ' although they are case-sensitive in C#.
        Console.WriteLine(person.firstname & " " & person.lastname)

        ' Getting the value of the Count property.
        ' The TryGetMember is not called, 
        ' because the property is defined in the class.
        Console.WriteLine("Number of dynamic properties:" & person.Count)

        ' The following statement throws an exception at run time.
        ' There is no "address" property,
        ' so the TryGetMember method returns false and this causes
        ' a MissingMemberException.
        ' Console.WriteLine(person.address)
    End Sub
End Module
' This examples has the following output:
' Ellen Adams
' Number of dynamic properties: 2

Inheritance Hierarchy

System..::.Object
System.Dynamic..::.DynamicObject
System.Windows.Interop..::.DynamicScriptObject

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Reference

DynamicObject Members

System.Dynamic Namespace