FirstChanceExceptionEventArgs Class
Provides data for the notification event that is raised when a managed exception first occurs, before the common language runtime begins searching for event handlers.
Assembly: mscorlib (in mscorlib.dll)
The FirstChanceExceptionEventArgs type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | FirstChanceExceptionEventArgs | Initializes a new instance of the FirstChanceExceptionEventArgs class with a specified exception. |
| Name | Description | |
|---|---|---|
![]() | Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
![]() | Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
![]() | GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
![]() | GetType | Gets the Type of the current instance. (Inherited from Object.) |
![]() | MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
![]() | ToString | Returns a string that represents the current object. (Inherited from Object.) |
This class provides the exception handler for the AppDomain.FirstChanceException event with access to the exception.
The following example creates a series of application domains named Child_0 through Child_3, with a Worker object in each application domain. Each Worker object has a reference to the Worker object in the next application domain, except for the Worker in the last application domain. The FirstChanceException event is handled in all application domains except Child_1.
When the application domains have been created, the default application domain calls the TestException method for the first child application domain. Each Worker object calls the TestException method for the next, until the last Worker throws an exception that is either handled or unhandled. Thus, the current thread passes through all the application domains, and TestException is added to the stack in each application domain.
When the last Worker object handles the exception, the FirstChanceException event is raised only in the last application domain. The other application domains never get a chance to handle the exception, so the event is not raised.
When the last Worker object does not handle the exception, the FirstChanceException event is raised in each application domain that has an event handler. After each event handler has finished, the stack continues to unwind until the exception is caught by the default application domain.
Note |
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To see how the stack display grows as the event is raised closer and closer to the default application domain, change e.Exception.Message to e.Exception in the FirstChanceHandler event handlers. Notice that when TestException is called across application domain boundaries, it appears twice: once for the proxy and once for the stub. |
Imports System.Reflection Imports System.Runtime.ExceptionServices Class Example Shared Sub Main() AddHandler AppDomain.CurrentDomain.FirstChanceException, AddressOf FirstChanceHandler ' Create a set of application domains, with a Worker object in each one. ' Each Worker object creates the next application domain. Dim ad As AppDomain = AppDomain.CreateDomain("AD0") Dim w As Worker = CType(ad.CreateInstanceAndUnwrap( Assembly.GetExecutingAssembly().FullName, "Worker"), Worker) w.Initialize(0, 3) Console.WriteLine(vbCrLf & "The last application domain throws an exception and catches it:") Console.WriteLine() w.TestException(true) Try Console.WriteLine(vbCrLf & "The last application domain throws an exception and does not catch it:") Console.WriteLine() w.TestException(false) Catch ex As ArgumentException Console.WriteLine("ArgumentException caught in {0}: {1}", AppDomain.CurrentDomain.FriendlyName, ex.Message) End Try End Sub Shared Sub FirstChanceHandler(ByVal source As Object, ByVal e As FirstChanceExceptionEventArgs) Console.WriteLine("FirstChanceException event raised in {0}: {1}", AppDomain.CurrentDomain.FriendlyName, e.Exception.Message) End Sub End Class Public Class Worker Inherits MarshalByRefObject Private ad As AppDomain = Nothing Private w As Worker = Nothing Public Sub Initialize(ByVal count As Integer, ByVal max As Integer) ' Handle the FirstChanceException event in all application domains except ' AD1. If count <> 1 AddHandler AppDomain.CurrentDomain.FirstChanceException, AddressOf FirstChanceHandler End If ' Create another application domain, until the maximum is reached. ' Field w remains Nothing in the last application domain, as a signal ' to TestException(). If count < max Dim nextAD As Integer = count + 1 ad = AppDomain.CreateDomain("AD" & nextAD) w = CType(ad.CreateInstanceAndUnwrap( Assembly.GetExecutingAssembly().FullName, "Worker"), Worker) w.Initialize(nextAD, max) End If End Sub Public Sub TestException(ByVal handled As Boolean) ' As long as there is another application domain, call TestException() on ' its Worker object. When the last application domain is reached, throw a ' handled or unhandled exception. If w IsNot Nothing w.TestException(handled) Else If handled Try Throw New ArgumentException("Thrown in " & AppDomain.CurrentDomain.FriendlyName) Catch ex As ArgumentException Console.WriteLine("ArgumentException caught in {0}: {1}", AppDomain.CurrentDomain.FriendlyName, ex.Message) End Try Else Throw New ArgumentException("Thrown in " & AppDomain.CurrentDomain.FriendlyName) End If End Sub Shared Sub FirstChanceHandler(ByVal source As Object, ByVal e As FirstChanceExceptionEventArgs) Console.WriteLine("FirstChanceException event raised in {0}: {1}", AppDomain.CurrentDomain.FriendlyName, e.Exception.Message) End Sub End Class ' This example produces output similar to the following: ' 'The last application domain throws an exception and catches it: ' 'FirstChanceException event raised in AD3: Thrown in AD3 'ArgumentException caught in AD3: Thrown in AD3 ' 'The last application domain throws an exception and does not catch it: ' 'FirstChanceException event raised in AD3: Thrown in AD3 'FirstChanceException event raised in AD2: Thrown in AD3 'FirstChanceException event raised in AD0: Thrown in AD3 'FirstChanceException event raised in Example.exe: Thrown in AD3 'ArgumentException caught in Example.exe: Thrown in AD3
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.



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