GCHandle.FromIntPtr(IntPtr) Metod

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

Parametrar

Returer

Ett nytt GCHandle objekt som motsvarar värdeparametern.

Attribut

SecurityCriticalAttribute

Undantag

Exempel

I följande kodexempel visas en App klass som skapar ett handtag till ett hanterat objekt med hjälp av GCHandle.Alloc metoden, vilket förhindrar att det hanterade objektet samlas in. Ett anrop till EnumWindows metoden skickar ett ombud och ett hanterat objekt (båda deklarerade som hanterade typer, men visas inte) och skickar handtaget till ett IntPtr objekt. Den ohanterade funktionen skickar tillbaka typen till anroparen som en parameter för återanropsfunktionen.

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