StreamingContextStates Enumeration
Defines a set of flags that specifies the source or destination context for the stream during serialization.
This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.
Namespace: System.Runtime.SerializationAssembly: mscorlib (in mscorlib.dll)
| Member name | Description | |
|---|---|---|
| CrossProcess | Specifies that the source or destination context is a different process on the same computer. | |
| CrossMachine | Specifies that the source or destination context is a different computer. | |
| File | Specifies that the source or destination context is a file. Users can assume that files will last longer than the process that created them and not serialize objects in such a way that deserialization will require accessing any data from the current process. | |
| Persistence | Specifies that the source or destination context is a persisted store, which could include databases, files, or other backing stores. Users can assume that persisted data will last longer than the process that created the data and not serialize objects so that deserialization will require accessing any data from the current process. | |
| Remoting | Specifies that the data is remoted to a context in an unknown location. Users cannot make any assumptions whether this is on the same computer. | |
| Other | Specifies that the serialization context is unknown. | |
| Clone | Specifies that the object graph is being cloned. Users can assume that the cloned graph will continue to exist within the same process and be safe to access handles or other references to unmanaged resources. | |
| CrossAppDomain | Specifies that the source or destination context is a different AppDomain. (For a description of AppDomains, see Application Domains). | |
| All | Specifies that the serialized data can be transmitted to or received from any of the other contexts. |
The following code example demonstrates the use of the StreamingContextStates enum.
Imports System Imports System.IO Imports System.Collections Imports System.Runtime.Serialization.Formatters.Binary Imports System.Runtime.Serialization Imports System.Runtime.InteropServices Imports System.Security.Permissions <Assembly: SecurityPermission( _ SecurityAction.RequestMinimum, Execution:=True)> ' This class includes several Win32 interop definitions. Friend Class Win32 Public Shared ReadOnly InvalidHandleValue As New IntPtr(-1) Public Const FILE_MAP_WRITE As Int32 = 2 Public Const PAGE_READWRITE As Int32 = &H4 <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function CreateFileMapping(ByVal hFile As IntPtr, _ ByVal pAttributes As IntPtr, _ ByVal flProtect As Int32, _ ByVal dwMaximumSizeHigh As Int32, _ ByVal dwMaximumSizeLow As Int32, _ ByVal pName As String) As IntPtr End Function <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function OpenFileMapping(ByVal dwDesiredAccess As Int32, _ ByVal bInheritHandle As Boolean, _ ByVal name As String) As IntPtr End Function <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function CloseHandle(ByVal handle As IntPtr) As Boolean End Function <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function MapViewOfFile(ByVal hFileMappingObject As IntPtr, _ ByVal dwDesiredAccess As Int32, _ ByVal dwFileOffsetHigh As Int32, _ ByVal dwFileOffsetLow As Int32, _ ByVal dwNumberOfBytesToMap As IntPtr) _ As IntPtr End Function <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function UnmapViewOfFile(ByVal address As IntPtr) As Boolean End Function <DllImport("Kernel32", CharSet:=CharSet.Unicode)> _ Public Shared Function DuplicateHandle(ByVal hSourceProcessHandle As IntPtr, _ ByVal hSourceHandle As IntPtr, _ ByVal hTargetProcessHandle As IntPtr, _ ByRef lpTargetHandle As IntPtr, _ ByVal dwDesiredAccess As Int32, _ ByVal bInheritHandle As Boolean, _ ByVal dwOptions As Int32) As Boolean End Function Public Const DUPLICATE_CLOSE_SOURCE As Int32 = &H1 Public Const DUPLICATE_SAME_ACCESS As Int32 = &H2 <DllImport("Kernel32", CharSet:=CharSet.Unicode)> Public Shared Function GetCurrentProcess() As IntPtr End Function End Class ' This class wraps memory that can be simultaneously ' shared by multiple AppDomains and Processes. <Serializable()> Public NotInheritable Class SharedMemory Implements ISerializable Implements IDisposable ' The handle and string that identify ' the Windows file-mapping object. Private m_hFileMap As IntPtr = IntPtr.Zero Private m_name As String ' The address of the memory-mapped file-mapping object. Private m_address As IntPtr <SecurityPermissionAttribute(SecurityAction.LinkDemand, _ Flags:=SecurityPermissionFlag.UnmanagedCode)> _ Public Function GetByte(ByVal offset As Int32) As Byte Dim b(0) As Byte Marshal.Copy(New IntPtr(m_address.ToInt64() + offset), b, 0, 1) Return b(0) End Function <SecurityPermissionAttribute(SecurityAction.LinkDemand, _ Flags:=SecurityPermissionFlag.UnmanagedCode)> _ Public Sub SetByte(ByVal offset As Int32, ByVal value As Byte) Dim b(0) As Byte b(0) = value Marshal.Copy(b, 0, New IntPtr(m_address.ToInt64() + offset), 1) End Sub ' The constructors. Public Sub New(ByVal size As Int32) Me.New(size, Nothing) End Sub Public Sub New(ByVal size As Int32, ByVal name As String) m_hFileMap = Win32.CreateFileMapping(Win32.InvalidHandleValue, _ IntPtr.Zero, Win32.PAGE_READWRITE, 0, size, name) If (m_hFileMap.Equals(IntPtr.Zero)) Then _ Throw New Exception("Could not create memory-mapped file.") m_name = name m_address = Win32.MapViewOfFile(m_hFileMap, _ Win32.FILE_MAP_WRITE, 0, 0, IntPtr.Zero) End Sub ' The cleanup methods. Public Sub Dispose() Implements IDisposable.Dispose GC.SuppressFinalize(Me) Dispose(True) End Sub Private Sub Dispose(ByVal disposing As Boolean) Win32.UnmapViewOfFile(m_address) Win32.CloseHandle(m_hFileMap) m_address = IntPtr.Zero m_hFileMap = IntPtr.Zero End Sub Protected Overrides Sub Finalize() Dispose(False) End Sub ' Private helper methods. Private Shared Function AllFlagsSet(ByVal flags As Int32, _ ByVal flagsToTest As Int32) As Boolean Return (flags And flagsToTest) = flagsToTest End Function Private Shared Function AnyFlagsSet(ByVal flags As Int32, _ ByVal flagsToTest As Int32) As Boolean Return (flags And flagsToTest) <> 0 End Function ' The security attribute demands that code that calls ' this method have permission to perform serialization. <SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter:=True)> _ Sub GetObjectData(ByVal info As SerializationInfo, _ ByVal context As StreamingContext) _ Implements ISerializable.GetObjectData ' The context's State member indicates where the object will be deserialized. ' A SharedMemory object cannot be serialized ' to any of the following destinations. Const InvalidDestinations As StreamingContextStates = _ StreamingContextStates.CrossMachine Or _ StreamingContextStates.File Or _ StreamingContextStates.Other Or _ StreamingContextStates.Persistence Or _ StreamingContextStates.Remoting If AnyFlagsSet(CType(context.State, Int32), _ CType(InvalidDestinations, Int32)) Then Throw New SerializationException("The SharedMemory object " & _ "cannot be serialized to any of the following streaming contexts: " _ & InvalidDestinations) End If Const DeserializableByHandle As StreamingContextStates = _ StreamingContextStates.Clone Or _ StreamingContextStates.CrossAppDomain If AnyFlagsSet(CType(context.State, Int32), _ CType(DeserializableByHandle, Int32)) Then info.AddValue("hFileMap", m_hFileMap) End If Const DeserializableByName As StreamingContextStates = _ StreamingContextStates.CrossProcess ' The same computer. If AnyFlagsSet(CType(context.State, Int32), CType(DeserializableByName, _ Int32)) Then If m_name = Nothing Then Throw New SerializationException("The SharedMemory object " & _ "cannot be serialized CrossProcess because it was not constructed " & _ "with a String name.") End If info.AddValue("name", m_name) End If End Sub Private Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext) ' The context's State member indicates where the object was serialized from. Const InvalidSources As StreamingContextStates = _ StreamingContextStates.CrossMachine Or _ StreamingContextStates.File Or _ StreamingContextStates.Other Or _ StreamingContextStates.Persistence Or _ StreamingContextStates.Remoting If AnyFlagsSet(CType(context.State, Int32), CType(InvalidSources, Int32)) Then Throw New SerializationException("The SharedMemory object " & _ "cannot be deserialized from any of the following stream contexts: " & _ InvalidSources) End If Const SerializedByHandle As StreamingContextStates = _ StreamingContextStates.Clone Or _ StreamingContextStates.CrossAppDomain ' The same process. If AnyFlagsSet(CType(context.State, Int32), _ CType(SerializedByHandle, Int32)) Then Try Win32.DuplicateHandle(Win32.GetCurrentProcess(), _ CType(info.GetValue("hFileMap", GetType(IntPtr)), IntPtr), _ Win32.GetCurrentProcess(), m_hFileMap, 0, False, _ Win32.DUPLICATE_SAME_ACCESS) Catch e As SerializationException Throw New SerializationException("A SharedMemory was not " & _ "serialized using any of the following streaming contexts: " & _ SerializedByHandle) End Try End If Const SerializedByName As StreamingContextStates = _ StreamingContextStates.CrossProcess ' The same computer. If AnyFlagsSet(CType(context.State, Int32), _ CType(SerializedByName, Int32)) Then Try m_name = info.GetString("name") Catch e As SerializationException Throw New SerializationException("A SharedMemory object " & _ "was not serialized using any of the following streaming contexts: " & _ SerializedByName) End Try m_hFileMap = Win32.OpenFileMapping(Win32.FILE_MAP_WRITE, False, m_name) End If If Not m_hFileMap.Equals(IntPtr.Zero) Then m_address = Win32.MapViewOfFile(m_hFileMap, _ Win32.FILE_MAP_WRITE, 0, 0, IntPtr.Zero) Else Throw New SerializationException("A SharedMemory object " & _ "could not be deserialized.") End If End Sub End Class Class App <STAThread()> Shared Sub Main() Serialize() Console.WriteLine() Deserialize() End Sub Shared Sub Serialize() ' Create a hashtable of values that will eventually be serialized. Dim sm As New SharedMemory(1024, "MyMemory") Dim x As Int32 For x = 0 To 99 sm.SetByte(x, x) Next Dim b(9) As Byte For x = 0 To b.Length - 1 b(x) = sm.GetByte(x) Next Console.WriteLine(BitConverter.ToString(b)) ' To serialize the hashtable (and its key/value pairs), you must first ' open a stream for writing. Use a file stream here. Dim fs As New FileStream("DataFile.dat", FileMode.Create) ' Construct a BinaryFormatter telling it where ' the objects will be serialized to. Dim formatter As New BinaryFormatter(Nothing, _ New StreamingContext(StreamingContextStates.CrossAppDomain)) Try formatter.Serialize(fs, sm) Catch e As SerializationException Console.WriteLine("Failed to serialize. Reason: " + e.Message) Throw Finally fs.Close() End Try End Sub Shared Sub Deserialize() ' Declare the hashtable reference. Dim sm As SharedMemory = Nothing ' Open the file containing the data that you want to deserialize. Dim fs As New FileStream("DataFile.dat", FileMode.Open) Try Dim Formatter As New BinaryFormatter(Nothing, _ New StreamingContext(StreamingContextStates.CrossAppDomain)) ' Deserialize the SharedMemory object from the file and ' assign the reference to the local variable. sm = DirectCast(Formatter.Deserialize(fs), SharedMemory) Catch e As SerializationException Console.WriteLine("Failed to deserialize. Reason: " & e.Message) Finally fs.Close() End Try ' To prove that the SharedMemory object deserialized correctly, ' display some of its bytes to the console. Dim b(9) As Byte Dim x As Int32 For x = 0 To b.Length - 1 b(x) = sm.GetByte(x) Next Console.WriteLine(BitConverter.ToString(b)) End Sub End Class
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.