GCHandle.Alloc 方法

定義

命名空間:

System.Runtime.InteropServices

組件:

System.Runtime.dll

配置指定物件的控制代碼。

多載

Alloc(Object)	配置 Normal 控制代碼給指定的物件。
Alloc(Object, GCHandleType)	配置指定類型的控制代碼給指定的物件。

Alloc(Object)

來源:

GCHandle.cs

配置 Normal 控制代碼給指定的物件。

public:
 static System::Runtime::InteropServices::GCHandle Alloc(System::Object ^ value);

public static System.Runtime.InteropServices.GCHandle Alloc (object? value);

static member Alloc : obj -> System.Runtime.InteropServices.GCHandle

Public Shared Function Alloc (value As Object) As GCHandle

參數

value

Object

使用 GCHandle 的物件。

傳回

GCHandle

保護物件不被記憶體回收的新 GCHandle。 當不再需要時，這個 GCHandle 必須使用 Free() 來釋放。

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

備註

Normal 句柄不透明，這表示您無法透過句柄解析它所包含的物件位址。

另請參閱

• GCHandleType

Alloc(Object, GCHandleType)

來源:

GCHandle.cs

配置指定類型的控制代碼給指定的物件。

public:
 static System::Runtime::InteropServices::GCHandle Alloc(System::Object ^ value, System::Runtime::InteropServices::GCHandleType type);

public static System.Runtime.InteropServices.GCHandle Alloc (object? value, System.Runtime.InteropServices.GCHandleType type);

static member Alloc : obj * System.Runtime.InteropServices.GCHandleType -> System.Runtime.InteropServices.GCHandle

Public Shared Function Alloc (value As Object, type As GCHandleType) As GCHandle

參數

value

Object

使用 GCHandle 的物件。

type

GCHandleType

GCHandleType 值的其中之一，指出要建立的 GCHandle 型別。

傳回

GCHandle

指定型別的新 GCHandle。 當不再需要時，這個 GCHandle 必須使用 Free() 來釋放。

例外狀況

ArgumentException

不可以 Pin 含有非基本 (非 Blittable) 成員的執行個體。

另請參閱

• GCHandleType