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AppDomain.AssemblyResolve Event

Updated: May 2010

Occurs when the resolution of an assembly fails.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Event AssemblyResolve As ResolveEventHandler
'Usage
Dim instance As AppDomain 
Dim handler As ResolveEventHandler 

AddHandler instance.AssemblyResolve, handler

Implements

_AppDomain.AssemblyResolve

For this event, the ResolveEventArgs.Name property returns the assembly name before policy is applied.

It is the responsibility of ResolveEventHandler for this event to return the assembly that resolves the type, assembly, or resource. The assembly must be loaded into an execution context; if it is loaded into the reflection-only context, the load that caused this event to be raised fails.

To register an event handler for this event, you must have the required permissions, or a SecurityException is thrown.

For more information about handling events, see Consuming Events.

The following example demonstrates the AssemblyResolve event.

For this code example to run, you must provide the fully qualified assembly name. For information about how to obtain the fully qualified assembly name, see Assembly Names.

Public Class MyType

    Public Sub New()
        Console.WriteLine()
        Console.WriteLine("MyType instantiated!")
    End Sub 'New 

End Class 'MyType

Class Test

    Public Shared Sub Main()
        Dim currentDomain As AppDomain = AppDomain.CurrentDomain

        ' This call will fail to create an instance of MyType since the 
        ' assembly resolver is not set
        InstantiateMyTypeFail(currentDomain)

        AddHandler currentDomain.AssemblyResolve, AddressOf MyResolveEventHandler

        ' This call will succeed in creating an instance of MyType since the 
        ' assembly resolver is now set.
        InstantiateMyTypeFail(currentDomain)

        ' This call will succeed in creating an instance of MyType since the 
        ' assembly name is valid.
        InstantiateMyTypeSucceed(currentDomain)
    End Sub 'Main

    Private Shared Sub InstantiateMyTypeFail(domain As AppDomain)
        ' Calling InstantiateMyType will always fail since the assembly info 
        ' given to CreateInstance is invalid. 
        Try 
            ' You must supply a valid fully qualified assembly name here.
            domain.CreateInstance("Assembly text name, Version, Culture, PublicKeyToken", "MyType")
        Catch e As Exception
            Console.WriteLine()
            Console.WriteLine(e.Message)
        End Try 
    End Sub 'InstantiateMyType

    Private Shared Sub InstantiateMyTypeSucceed(domain As AppDomain)
        Try 
            Dim asmname As String = Assembly.GetCallingAssembly().FullName
            domain.CreateInstance(asmname, "MyType")
        Catch e As Exception
            Console.WriteLine()
            Console.WriteLine(e.Message)
        End Try 
    End Sub 

    Private Shared Function MyResolveEventHandler(sender As Object, args As ResolveEventArgs) As Assembly
        Console.WriteLine("Resolving...")
        Return GetType(MyType).Assembly
    End Function 'MyResolveEventHandler

End Class 'Test

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

Date

History

Reason

May 2010

Clarification: The returned assembly must be loaded into an execution context, not the reflection-only context.

Customer feedback.

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