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GCHandle.FromIntPtr(IntPtr) Metodo

Definizione

Restituisce un nuovo oggetto GCHandle creato da un handle per un oggetto gestito.

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

Parametri

value
IntPtr

nativeint

Handle IntPtr per un oggetto gestito da cui creare un oggetto GCHandle.

Restituisce

Nuovo oggetto GCHandle corrispondente al parametro value.

Attributi

Eccezioni

Il valore del parametro value è Zero.

Esempio

Nell'esempio di codice seguente viene illustrata una App classe che crea un handle per un oggetto gestito usando il GCHandle.Alloc metodo , che impedisce la raccolta dell'oggetto gestito. Una chiamata al EnumWindows metodo passa un delegato e un oggetto gestito (entrambi dichiarati come tipi gestiti, ma non visualizzati) ed esegue il cast dell'handle a un IntPtr oggetto . La funzione non gestita passa nuovamente il tipo al chiamante come parametro della funzione di callback.

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

Si applica a