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StreamingContext.State Property

Gets the source or destination of the transmitted data.

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

public StreamingContextStates State { get; }
/** @property */
public StreamingContextStates get_State ()

public function get State () : StreamingContextStates

Not applicable.

Property Value

During serialization, the destination of the transmitted data. During deserialization, the source of the data.

During serialization, the current property specifies the destination of the transmitted data. For example, when serializing data from cross-AppDomain remoting, the StreamingContextStates is CrossProcess. During deserialization, the state indicates the source of the deserialized stream.

// Note: You must compile this file using the C# /unsafe switch.
using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization;
using System.Runtime.InteropServices;
using System.Security.Permissions;

[assembly: SecurityPermission(
SecurityAction.RequestMinimum, Execution = true)]
// This class includes several Win32 interop definitions.
internal class Win32
{
    public static readonly IntPtr InvalidHandleValue = new IntPtr(-1);
    public const UInt32 FILE_MAP_WRITE = 2;
    public const UInt32 PAGE_READWRITE = 0x04;

    [DllImport("Kernel32")]
    public static extern IntPtr CreateFileMapping(IntPtr hFile,
        IntPtr pAttributes, UInt32 flProtect,
        UInt32 dwMaximumSizeHigh, UInt32 dwMaximumSizeLow, String pName);

    [DllImport("Kernel32")]
    public static extern IntPtr OpenFileMapping(UInt32 dwDesiredAccess,
        Boolean bInheritHandle, String name);

    [DllImport("Kernel32")]
    public static extern Boolean CloseHandle(IntPtr handle);

    [DllImport("Kernel32")]
    public static extern IntPtr MapViewOfFile(IntPtr hFileMappingObject,
        UInt32 dwDesiredAccess,
        UInt32 dwFileOffsetHigh, UInt32 dwFileOffsetLow,
        IntPtr dwNumberOfBytesToMap);

    [DllImport("Kernel32")]
    public static extern Boolean UnmapViewOfFile(IntPtr address);

    [DllImport("Kernel32")]
    public static extern Boolean DuplicateHandle(IntPtr hSourceProcessHandle,
        IntPtr hSourceHandle,
        IntPtr hTargetProcessHandle, ref IntPtr lpTargetHandle,
        UInt32 dwDesiredAccess, Boolean bInheritHandle, UInt32 dwOptions);
    public const UInt32 DUPLICATE_CLOSE_SOURCE = 0x00000001;
    public const UInt32 DUPLICATE_SAME_ACCESS = 0x00000002;

    [DllImport("Kernel32")]
    public static extern IntPtr GetCurrentProcess();
}


// This class wraps memory that can be simultaneously 
// shared by multiple AppDomains and Processes.
[Serializable]
public sealed class SharedMemory : ISerializable, IDisposable
{
    // The handle and string that identify 
    // the Windows file-mapping object.
    private IntPtr m_hFileMap = IntPtr.Zero;
    private String m_name;

    // The address of the memory-mapped file-mapping object.
    private IntPtr m_address;

    public unsafe Byte* Address
    {
        get { return (Byte*)m_address; }
    }

    // The constructors.
    public SharedMemory(Int32 size) : this(size, null) { }

    public SharedMemory(Int32 size, String name)
    {
        m_hFileMap = Win32.CreateFileMapping(Win32.InvalidHandleValue,
            IntPtr.Zero, Win32.PAGE_READWRITE,
            0, unchecked((UInt32)size), name);
        if (m_hFileMap == IntPtr.Zero)
            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);
    }

    // The cleanup methods.
    public void Dispose()
    {
        GC.SuppressFinalize(this);
        Dispose(true);
    }

    private void Dispose(Boolean disposing)
    {
        Win32.UnmapViewOfFile(m_address);
        Win32.CloseHandle(m_hFileMap);
        m_address = IntPtr.Zero;
        m_hFileMap = IntPtr.Zero;
    }

    ~SharedMemory()
    {
        Dispose(false);
    }

    // Private helper methods.
    private static Boolean AllFlagsSet(Int32 flags, Int32 flagsToTest)
    {
        return (flags & flagsToTest) == flagsToTest;
    }

    private static Boolean AnyFlagsSet(Int32 flags, Int32 flagsToTest)
    {
        return (flags & flagsToTest) != 0;
    }


    // The security attribute demands that code that calls  
    // this method have permission to perform serialization.
    [SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter = true)]
    void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
    {
        // 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 StreamingContextStates InvalidDestinations =
                  StreamingContextStates.CrossMachine |
                  StreamingContextStates.File |
                  StreamingContextStates.Other |
                  StreamingContextStates.Persistence |
                  StreamingContextStates.Remoting;
        if (AnyFlagsSet((Int32)context.State, (Int32)InvalidDestinations))
            throw new SerializationException("The SharedMemory object " +
                "cannot be serialized to any of the following streaming contexts: " +
                InvalidDestinations);

        const StreamingContextStates DeserializableByHandle =
                  StreamingContextStates.Clone |
            // The same process.
                  StreamingContextStates.CrossAppDomain;
        if (AnyFlagsSet((Int32)context.State, (Int32)DeserializableByHandle))
            info.AddValue("hFileMap", m_hFileMap);

        const StreamingContextStates DeserializableByName =
            // The same computer.
                  StreamingContextStates.CrossProcess;
        if (AnyFlagsSet((Int32)context.State, (Int32)DeserializableByName))
        {
            if (m_name == null)
                throw new SerializationException("The SharedMemory object " +
                    "cannot be serialized CrossProcess because it was not constructed " +
                    "with a String name.");
            info.AddValue("name", m_name);
        }
    }


    // The security attribute demands that code that calls  
    // this method have permission to perform serialization.
    [SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter = true)]
    private SharedMemory(SerializationInfo info, StreamingContext context)
    {
        // The context's State member indicates 
        // where the object was serialized from.

        const StreamingContextStates InvalidSources =
                  StreamingContextStates.CrossMachine |
                  StreamingContextStates.File |
                  StreamingContextStates.Other |
                  StreamingContextStates.Persistence |
                  StreamingContextStates.Remoting;
        if (AnyFlagsSet((Int32)context.State, (Int32)InvalidSources))
            throw new SerializationException("The SharedMemory object " +
                "cannot be deserialized from any of the following stream contexts: " +
                InvalidSources);

        const StreamingContextStates SerializedByHandle =
                  StreamingContextStates.Clone |
            // The same process.
                  StreamingContextStates.CrossAppDomain;
        if (AnyFlagsSet((Int32)context.State, (Int32)SerializedByHandle))
        {
            try
            {
                Win32.DuplicateHandle(Win32.GetCurrentProcess(),
                    (IntPtr)info.GetValue("hFileMap", typeof(IntPtr)),
                    Win32.GetCurrentProcess(), ref m_hFileMap, 0, false,
                    Win32.DUPLICATE_SAME_ACCESS);
            }
            catch (SerializationException)
            {
                throw new SerializationException("A SharedMemory was not serialized " +
                    "using any of the following streaming contexts: " +
                    SerializedByHandle);
            }
        }

        const StreamingContextStates SerializedByName =
            // The same computer.
                  StreamingContextStates.CrossProcess;
        if (AnyFlagsSet((Int32)context.State, (Int32)SerializedByName))
        {
            try
            {
                m_name = info.GetString("name");
            }
            catch (SerializationException)
            {
                throw new SerializationException("A SharedMemory object was not " +
                    "serialized using any of the following streaming contexts: " +
                    SerializedByName);
            }
            m_hFileMap = Win32.OpenFileMapping(Win32.FILE_MAP_WRITE, false, m_name);
        }
        if (m_hFileMap != IntPtr.Zero)
        {
            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.");
        }
    }
}


class App
{
    [STAThread]
    static void Main(string[] args)
    {
        Serialize();
        Console.WriteLine();
        Deserialize();
    }

    unsafe static void Serialize()
    {
        // Create a hashtable of values that will eventually be serialized.
        SharedMemory sm = new SharedMemory(1024, "JeffMemory");
        for (Int32 x = 0; x < 100; x++)
            *(sm.Address + x) = (Byte)x;

        Byte[] b = new Byte[10];
        for (Int32 x = 0; x < b.Length; x++) b[x] = *(sm.Address + x);
        Console.WriteLine(BitConverter.ToString(b));

        // To serialize the SharedMemory object, 
        // you must first open a stream for writing. 
        // Use a file stream here.
        FileStream fs = new FileStream("DataFile.dat", FileMode.Create);

        // Construct a BinaryFormatter and tell it where 
        // the objects will be serialized to.
        BinaryFormatter formatter = new BinaryFormatter(null,
            new StreamingContext(StreamingContextStates.CrossAppDomain));
        try
        {
            formatter.Serialize(fs, sm);
        }
        catch (SerializationException e)
        {
            Console.WriteLine("Failed to serialize. Reason: " + e.Message);
            throw;
        }
        finally
        {
            fs.Close();
        }
    }


    unsafe static void Deserialize()
    {
        // Declare a SharedMemory reference.
        SharedMemory sm = null;

        // Open the file containing the data that you want to deserialize.
        FileStream fs = new FileStream("DataFile.dat", FileMode.Open);
        try
        {
            BinaryFormatter formatter = new BinaryFormatter(null,
                new StreamingContext(StreamingContextStates.CrossAppDomain));

            // Deserialize the SharedMemory object from the file and 
            // assign the reference to the local variable.
            sm = (SharedMemory)formatter.Deserialize(fs);
        }
        catch (SerializationException e)
        {
            Console.WriteLine("Failed to deserialize. Reason: " + e.Message);
            throw;
        }
        finally
        {
            fs.Close();
        }

        // To prove that the SharedMemory object deserialized correctly, 
        // display some of its bytes to the console.
        Byte[] b = new Byte[10];
        for (Int32 x = 0; x < b.Length; x++) b[x] = *(sm.Address + x);
        Console.WriteLine(BitConverter.ToString(b));
    }
}

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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

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