GCHandle.Alloc 方法

定义

命名空间:

System.Runtime.InteropServices

程序集:

System.Runtime.dll

为指定的对象分配句柄。

重载

Alloc(Object)	为指定的对象分配 Normal 句柄。
Alloc(Object, GCHandleType)	为指定的对象分配指定类型的句柄。

Alloc(Object)

Source:

GCHandle.cs

为指定的对象分配 Normal 句柄。

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

参数

value

Object

使用 GCHandle 的对象。

返回

GCHandle

一个新的 GCHandle，它保护对象不被垃圾回收。 当不再需要 GCHandle 时，必须通过 Free() 将其释放。

示例

下面的示例演示了一个 App 类，该类使用 GCHandle.Alloc 方法创建托管对象的句柄，该方法阻止收集托管对象。 对 方法的 EnumWindows 调用传递委托和托管对象 (声明为托管类型，但不) 显示，并将句柄 IntPtr强制转换为 。 非托管函数将类型作为回调函数的参数传递回调用方。

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

注解

Normal 句柄是不透明的，这意味着无法通过句柄解析它所包含的对象的地址。

另请参阅

• GCHandleType

Alloc(Object, GCHandleType)

Source:

GCHandle.cs

为指定的对象分配指定类型的句柄。

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

参数

value

Object

使用 GCHandle 的对象。

type

GCHandleType

GCHandleType 值之一，指示要创建的 GCHandle 的类型。

返回

GCHandle

指定的类型的新 GCHandle。 当不再需要 GCHandle 时，必须通过 Free() 将其释放。

例外

ArgumentException

具有非基元（非直接复制到本机结构中的）成员的实例不能被固定。

另请参阅

• GCHandleType