GCHandle.Free Méthode

Définition

Libère un GCHandle.Releases a GCHandle.

public:
 void Free();
[System.Security.SecurityCritical]
public void Free ();
member this.Free : unit -> unit
Public Sub Free ()
Attributs

Exceptions

Le handle a été libéré ou n'a jamais été initialisé.The handle was freed or never initialized.

Exemples

L’exemple suivant illustre une App classe qui crée un handle vers un objet managé à l' GCHandle.Alloc aide de la méthode, ce qui empêche la collecte de l’objet managé.The following example shows an App class that creates a handle to a managed object using the GCHandle.Alloc method, which prevents the managed object from being collected. Un appel à la EnumWindows méthode passe un délégué et un objet managé (tous deux déclarés comme types managés, mais non affichés) et effectue un cast du IntPtrhandle vers un.A call to the EnumWindows method passes a delegate and a managed object (both declared as managed types, but not shown), and casts the handle to an IntPtr. La fonction non managée passe le type à l’appelant en tant que paramètre de la fonction de rappel.The unmanaged function passes the type back to the caller as a parameter of the callback function.

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

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();
    }

    [SecurityPermission(SecurityAction.Demand, UnmanagedCode = true)]
    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

Remarques

L’appelant doit s’assurer que, pour un handle Free donné, est appelé une seule fois.The caller must ensure that for a given handle, Free is called only once.

Sécurité

SecurityCriticalAttribute
Requiert une confiance totale pour l’appelant immédiat.requires full trust for the immediate caller. Ce membre ne peut pas être utilisé par du code de confiance partielle ou transparent.This member cannot be used by partially trusted or transparent code.

S’applique à