GCHandle.Target GCHandle.Target GCHandle.Target GCHandle.Target Property

定義

取得或設定這個控制代碼表示的物件。Gets or sets the object this handle represents.

public:
 property System::Object ^ Target { System::Object ^ get(); void set(System::Object ^ value); };
[get: System.Security.SecurityCritical]
[set: System.Security.SecurityCritical]
public object Target { get; set; }
member this.Target : obj with get, set
Public Property Target As Object

屬性值

這個控制代碼表示的物件。The object this handle represents.

例外狀況

控制代碼已釋放,或從未初始化。The handle was freed, or never initialized.

範例

下列範例顯示App的類別,會GCHandle.Alloc使用方法建立 managed 物件的控制碼,以防止收集 managed 物件。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. EnumWindows方法的呼叫會傳遞委派和 managed 物件(兩者都宣告為 managed 類型,但不會顯示),並將控制碼轉換IntPtr成。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. 非受控函式會將型別傳遞回呼叫端做為回呼函式的參數。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

安全性

SecurityCriticalAttribute
需要完全信任立即呼叫者。requires full trust for the immediate caller. 部分信任或透明的程式碼無法使用這個成員。This member cannot be used by partially trusted or transparent code.

適用於

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