Я придумала шаблон, который кажется довольно хорошим. Это вдохновлено кем-то, размещенным на CodeProject.com - использующим список для отслеживания одноразовых товаров; raiiBase (из T) - это базовый класс, подходящий для любого класса, конструктор которого принимает один параметр. Конструктор класса должен быть защищен, а конструирование должно выполняться методом фабрики. Статический конструктор makeRaii () доставляет делегат к фабричной функции, которая должна принимать стек (из iDisposable) вместе с параметром ожидаемого типа класса. Пример использования:
Public Class RaiiTest
Inherits raiiBase(Of String)
Dim thing1 As testDisposable = RAII(New testDisposable("Moe " & creationParam, "a"))
Dim thing2 As testDisposable = RAII(New testDisposable("Larry " & creationParam, "b"))
Dim thing3 As testDisposable = RAII(New testDisposable("Shemp " & creationParam, "c"))
Dim thing4 As testDisposable = RAII(New testDisposable("Curly " & creationParam, "d"))
Protected Sub New(ByVal dispList As Stack(Of IDisposable), ByVal newName As String)
MyBase.New(dispList, newName)
End Sub
Private Shared Function _newRaiiTest(ByVal dispList As Stack(Of IDisposable), ByVal theName As String) As RaiiTest
Return New RaiiTest(dispList, theName)
End Function
Public Shared Function newRaiiTest(ByVal theName As String) As RaiiTest
Return makeRaii(Of RaiiTest)(AddressOf _newRaiiTest, theName)
End Function
Shared Sub test(ByVal st As String)
Try
Using it As RaiiTest = newRaiiTest(st)
Debug.Print("Now using object")
End Using
Debug.Print("No exceptions thrown")
Catch ex As raiiException
Debug.Print("Output exception: " & ex.Message)
If ex.InnerException IsNot Nothing Then Debug.Print("Inner exception: " & ex.InnerException.Message)
For Each exx As Exception In ex.DisposalExceptions
Debug.Print("Disposal exception: " & exx.Message)
Next
Catch ex As Exception
Debug.Print("Misc. exception: " & ex.Message)
End Try
End Sub
End Class
Поскольку raiiTest наследует raiiBase (из String), для создания экземпляра класса вызовите newRaiiTest со строковым параметром. RAII () - это универсальная функция, которая регистрирует свой аргумент как iDisposable, который необходимо очистить, а затем вернуть его. Все зарегистрированные одноразовые материалы будут утилизироваться при вызове Dispose для основного объекта или при возникновении исключения в конструкции основного объекта.
Вот класс riaaBase:
Option Strict On
Class raiiException
Inherits Exception
ReadOnly _DisposalExceptions() As Exception
Sub New(ByVal message As String, ByVal InnerException As Exception, ByVal allInnerExceptions As Exception())
MyBase.New(message, InnerException)
_DisposalExceptions = allInnerExceptions
End Sub
Public Overridable ReadOnly Property DisposalExceptions() As Exception()
Get
Return _DisposalExceptions
End Get
End Property
End Class
Public Class raiiBase(Of T)
Implements IDisposable
Protected raiiList As Stack(Of IDisposable)
Protected creationParam As T
Delegate Function raiiFactory(Of TT As raiiBase(Of T))(ByVal theList As Stack(Of IDisposable), ByVal theParam As T) As TT
Shared Function CopyFirstParamToSecondAndReturnFalse(Of TT)(ByVal P1 As TT, ByRef P2 As TT) As Boolean
P2 = P1
Return False
End Function
Shared Function makeRaii(Of TT As raiiBase(Of T))(ByVal theFactory As raiiFactory(Of TT), ByVal theParam As T) As TT
Dim dispList As New Stack(Of IDisposable)
Dim constructionFailureException As Exception = Nothing
Try
Return theFactory(dispList, theParam)
Catch ex As Exception When CopyFirstParamToSecondAndReturnFalse(ex, constructionFailureException)
' The above statement let us find out what exception occurred without having to catch and rethrow
Throw ' Should never happen, since we should have returned false above
Finally
If constructionFailureException IsNot Nothing Then
zapList(dispList, constructionFailureException)
End If
End Try
End Function
Protected Sub New(ByVal DispList As Stack(Of IDisposable), ByVal Params As T)
Me.raiiList = DispList
Me.creationParam = Params
End Sub
Public Shared Sub zapList(ByVal dispList As IEnumerable(Of IDisposable), ByVal triggerEx As Exception)
Using theEnum As IEnumerator(Of IDisposable) = dispList.GetEnumerator
Try
While theEnum.MoveNext
theEnum.Current.Dispose()
End While
Catch ex As Exception
Dim exList As New List(Of Exception)
exList.Add(ex)
While theEnum.MoveNext
Try
theEnum.Current.Dispose()
Catch ex2 As Exception
exList.Add(ex2)
End Try
End While
Throw New raiiException("RAII failure", triggerEx, exList.ToArray)
End Try
End Using
End Sub
Function RAII(Of U As IDisposable)(ByVal Thing As U) As U
raiiList.Push(Thing)
Return Thing
End Function
Shared Sub zap(ByVal Thing As IDisposable)
If Thing IsNot Nothing Then Thing.Dispose()
End Sub
Private raiiBaseDisposeFlag As Integer = 0 ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(ByVal disposing As Boolean)
If disposing AndAlso Threading.Interlocked.Exchange(raiiBaseDisposeFlag, 1) = 0 Then
zapList(raiiList, Nothing)
End If
End Sub
#Region " IDisposable Support "
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
End Class
Обратите внимание, что пользовательский тип исключения будет выдан, если удаление не удастся для любого или всех зарегистрированных одноразовых объектов. InnerException будет указывать, не сработал ли конструктор; чтобы узнать, какие диспенсеры не удалось, проверьте DisposalExceptions.