GCHandle.Target 屬性

public:
 property System::Object ^ Target { System::Object ^ get(); void set(System::Object ^ value); };

public object Target { [System.Security.SecurityCritical] get; [System.Security.SecurityCritical] set; }

public object? Target { get; set; }

public object Target { get; set; }

[<get: System.Security.SecurityCritical>]
[<set: System.Security.SecurityCritical>]
member this.Target : obj with get, set

member this.Target : obj with get, set

Public Property Target As Object

屬性值

這個把柄所代表的物件。

屬性

SecurityCriticalAttribute

例外狀況

範例

以下範例展示了 App 一個類別，該類別使用 該方法建立一個 handle 到 受 GCHandle.Alloc 管理物件，阻止該受管理物件被收集。 呼叫該 EnumWindows 方法會傳遞代理（deleged）和受管理物件（兩者皆宣告為受管理型別，但未顯示），並將 handle 投射為 IntPtr。 未管理函式會將型別作為回調函式的參數傳回呼叫者。

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

另請參閱

• GCHandleType