GCHandle.Target Properti
Definisi
Penting
Beberapa informasi terkait produk prarilis yang dapat diubah secara signifikan sebelum dirilis. Microsoft tidak memberikan jaminan, tersirat maupun tersurat, sehubungan dengan informasi yang diberikan di sini.
Mendapatkan atau mengatur objek yang diwakili handel ini.
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
Nilai Properti
Objek yang diwakili oleh handel ini.
- Atribut
Pengecualian
Handel dikosongkan, atau tidak pernah diinisialisasi.
Contoh
Contoh berikut menunjukkan App
kelas yang membuat handel ke objek terkelola menggunakan GCHandle.Alloc
metode , yang mencegah objek terkelola dikumpulkan. Panggilan ke EnumWindows
metode meneruskan delegasi dan objek terkelola (keduanya dinyatakan sebagai jenis terkelola, tetapi tidak ditampilkan), dan melemparkan handel ke IntPtr. Fungsi yang tidak dikelola meneruskan jenis kembali ke pemanggil sebagai parameter fungsi panggilan balik.
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