GCHandle.FromIntPtr(IntPtr) Método

  • Referencia

Definición

Espacio de nombres:
System.Runtime.InteropServices
Ensamblado:
System.Runtime.InteropServices.dll
Ensamblado:
System.Runtime.dll
Ensamblado:
mscorlib.dll
Ensamblado:
netstandard.dll
Source:
GCHandle.cs
Source:
GCHandle.cs
Source:
GCHandle.cs

Devuelve un nuevo objeto GCHandle creado a partir de un identificador a un objeto administrado.

public:
 static System::Runtime::InteropServices::GCHandle FromIntPtr(IntPtr value);
[System.Security.SecurityCritical]
public static System.Runtime.InteropServices.GCHandle FromIntPtr (IntPtr value);
public static System.Runtime.InteropServices.GCHandle FromIntPtr (IntPtr value);
[<System.Security.SecurityCritical>]
static member FromIntPtr : nativeint -> System.Runtime.InteropServices.GCHandle
static member FromIntPtr : nativeint -> System.Runtime.InteropServices.GCHandle
Public Shared Function FromIntPtr (value As IntPtr) As GCHandle

Parámetros

value
IntPtr

nativeint

Identificador IntPtr a un objeto administrado del que se va a crear un objeto GCHandle.

Devoluciones

GCHandle

Nuevo objeto GCHandle que corresponde al parámetro de valor.

Atributos
SecurityCriticalAttribute

Excepciones

InvalidOperationException

El valor del parámetro value es Zero.

Ejemplos

En el ejemplo de código siguiente se muestra una App clase que crea un identificador para un objeto administrado mediante el GCHandle.Alloc método , lo que impide que se recopile el objeto administrado. Una llamada al EnumWindows método pasa un delegado y un objeto administrado (ambos declarados como tipos administrados, pero no mostrados) y convierte el identificador en un IntPtr objeto . La función no administrada pasa el tipo al autor de la llamada como parámetro de la función de devolución de llamada.

using System;
using System.IO;
using System.Threading;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public delegate bool CallBack(int handle, IntPtr param);

internal static class NativeMethods
{
    // passing managed object as LPARAM
    // BOOL EnumWindows(WNDENUMPROC lpEnumFunc, LPARAM lParam);

    [DllImport("user32.dll")]
    internal static extern bool EnumWindows(CallBack cb, IntPtr param);
}

public class App
{
    public static void Main()
    {
        Run();
    }

    public static void Run()
    {
        TextWriter tw = Console.Out;
        GCHandle gch = GCHandle.Alloc(tw);

        CallBack cewp = new CallBack(CaptureEnumWindowsProc);

        // platform invoke will prevent delegate to be garbage collected
        // before call ends

        NativeMethods.EnumWindows(cewp, GCHandle.ToIntPtr(gch));
        gch.Free();
    }

    private static bool CaptureEnumWindowsProc(int handle, IntPtr param)
    {
        GCHandle gch = GCHandle.FromIntPtr(param);
        TextWriter tw = (TextWriter)gch.Target;
        tw.WriteLine(handle);
        return true;
    }
}

Imports System.IO
Imports System.Threading
Imports System.Windows.Forms
Imports System.Runtime.InteropServices
Imports System.Security.Permissions

Public Delegate Function CallBack(ByVal handle As Integer, ByVal param As IntPtr) As Boolean


Friend Module NativeMethods

    ' passing managed object as LPARAM
    ' BOOL EnumWindows(WNDENUMPROC lpEnumFunc, LPARAM lParam);
    <DllImport("user32.dll")>
    Friend Function EnumWindows(ByVal cb As CallBack, ByVal param As IntPtr) As Boolean
    End Function
End Module


Module App

    Sub Main()

        Run()

    End Sub

    <SecurityPermission(SecurityAction.Demand, UnmanagedCode:=True)>
    Sub Run()

        Dim tw As TextWriter = Console.Out
        Dim gch As GCHandle = GCHandle.Alloc(tw)

        Dim cewp As CallBack
        cewp = AddressOf CaptureEnumWindowsProc

        ' platform invoke will prevent delegate to be garbage collected
        ' before call ends
        NativeMethods.EnumWindows(cewp, GCHandle.ToIntPtr(gch))
        gch.Free()

    End Sub


    Function CaptureEnumWindowsProc(ByVal handle As Integer, ByVal param As IntPtr) As Boolean
        Dim gch As GCHandle = GCHandle.FromIntPtr(param)
        Dim tw As TextWriter = CType(gch.Target, TextWriter)
        tw.WriteLine(handle)
        Return True

    End Function
End Module

Se aplica a