GCHandle.Target 屬性

定義

命名空間:

System.Runtime.InteropServices

組件:

System.Runtime.dll

來源:

GCHandle.cs

取得或設定這個控制代碼表示的物件。

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

public object? Target { get; set; }

member this.Target : obj with get, set

Public Property Target As Object

屬性值

Object

這個控制代碼表示的物件。

例外狀況

InvalidOperationException

控制代碼已釋放，或從未初始化。

範例

下列範例示範使用 App 方法建立Managed物件的 GCHandle.Alloc 句柄的類別，以防止收集Managed物件。 呼叫 方法會 EnumWindows 傳遞委派和 Managed 物件， (宣告為 Managed 型別，但未顯示) ，並將句柄 IntPtr轉換成 。 Unmanaged 函式會將型別傳回給呼叫端做為回呼函式的參數。

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