AppDomain.TypeResolve Event


The .NET API Reference documentation has a new home. Visit the .NET API Browser on to see the new experience.

Occurs when the resolution of a type fails.

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

Public Event TypeResolve As ResolveEventHandler

The TypeResolve event occurs when the common language runtime is unable to determine the assembly that can create the requested type. This can occur if the type is defined in a dynamic assembly, or the type is not defined in a dynamic assembly but the runtime does not know which assembly the type is defined in. The latter situation can occur when Type.GetType is called with a type name that is not qualified with the assembly name.

The ResolveEventHandler for this event can attempt to locate and create the type.

However, the TypeResolve event does not occur if the runtime knows it is not possible to find a type in certain assemblies. For example, this event does not occur if the type is not found in a static assembly because the runtime knows types cannot be added dynamically to static assemblies.

Beginning with the .NET Framework 4, the ResolveEventArgs.RequestingAssembly property contains the assembly that requested the type. For more information, see ResolveEventArgs.RequestingAssembly.

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 Handling and Raising Events.

The following sample demonstrates the TypeResolve 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.

Option Strict On
Option Explicit On

Imports System
Imports System.Reflection
Imports System.Reflection.Emit

Module Test

    ' For this code example, the following information needs to be
    ' available to both Main and the HandleTypeResolve event
    ' handler:
    Private ab As AssemblyBuilder
    Private moduleName As String

    Sub Main() 

        Dim currDom As AppDomain = AppDomain.CurrentDomain

        ' Create a dynamic assembly with one module, to be saved to 
        ' disk (AssemblyBuilderAccess.Save).
        Dim aName As AssemblyName = new AssemblyName()
        aName.Name = "Transient"
        moduleName = aName.Name + ".dll"
        ab = currDom.DefineDynamicAssembly(aName, _
        Dim mb As ModuleBuilder = _
            ab.DefineDynamicModule(aName.Name, moduleName)

        ' The dynamic assembly has just one dummy type, to demonstrate
        ' type resolution.
        Dim tb As TypeBuilder = mb.DefineType("Example")

        ' First, try to load the type without saving the dynamic 
        ' assembly and without hooking up the TypeResolve event. The
        ' type cannot be loaded.
            Dim temp As Type = Type.GetType("Example", true)
            Console.WriteLine("Loaded type {0}.", temp)
        Catch ex As TypeLoadException
            Console.WriteLine("Loader could not resolve the type.")
        End Try

        ' Hook up the TypeResolve event.
        AddHandler currDom.TypeResolve, AddressOf HandleTypeResolve

        ' Now try to load the type again. The TypeResolve event is 
        ' raised, the dynamic assembly is saved, and the dummy type is
        ' loaded successfully. Display it to the console, and create
        ' an instance.
        Dim t As Type = Type.GetType("Example", true)
        Console.WriteLine("Loaded type ""{0}"".", t)
        Dim o As Object = Activator.CreateInstance(t)
    End Sub

    Private Function HandleTypeResolve(ByVal sender As Object, _
        ByVal e As ResolveEventArgs) As [Assembly]

        Console.WriteLine("TypeResolve event handler.")

        ' Save the dynamic assembly, and then load it using its
        ' display name. Return the loaded assembly.
        Return [Assembly].Load(ab.FullName) 
    End Function
End Module

' This code example produces the following output:
'Loader could not resolve the type.
'TypeResolve event handler.
'Loaded type "Example".


requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

.NET Framework
Available since 1.1
Return to top