GCHandle.Alloc Method

Definition

为指定的对象分配句柄。Allocates a handle for the specified object.

Overloads

Alloc(Object)

为指定的对象分配 Normal 句柄。Allocates a Normal handle for the specified object.

Alloc(Object, GCHandleType)

为指定的对象分配指定类型的句柄。Allocates a handle of the specified type for the specified object.

Alloc(Object)

为指定的对象分配 Normal 句柄。Allocates a Normal handle for the specified object.

public:
 static System::Runtime::InteropServices::GCHandle Alloc(System::Object ^ value);
[System.Security.SecurityCritical]
public static System.Runtime.InteropServices.GCHandle Alloc (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

Parameters

value
Object

使用 GCHandle 的对象。The object that uses the GCHandle.

Returns

GCHandle

一个新的 GCHandle,它保护对象不被垃圾回收。A new GCHandle that protects the object from garbage collection. 当不再需要 GCHandle 时,必须通过 Free() 将其释放。This GCHandle must be released with Free() when it is no longer needed.

Attributes

Examples

下面的示例演示一个 App 类,该类使用 GCHandle.Alloc 方法创建托管对象的句柄,这会阻止收集托管的对象。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 方法的调用会传递委托和托管对象(两者都声明为托管类型,但不显示),并将句柄强制转换为 IntPtrA 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. 非托管函数将该类型作为回调函数的参数传递回调用方。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

Remarks

Normal 句柄是不透明的,这意味着你不能通过句柄解析它包含的对象的地址。Normal handles are opaque, which means that you cannot resolve the address of the object it contains through the handle.

See also

Alloc(Object, GCHandleType)

为指定的对象分配指定类型的句柄。Allocates a handle of the specified type for the specified object.

public:
 static System::Runtime::InteropServices::GCHandle Alloc(System::Object ^ value, System::Runtime::InteropServices::GCHandleType type);
[System.Security.SecurityCritical]
public static System.Runtime.InteropServices.GCHandle Alloc (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

Parameters

value
Object

使用 GCHandle 的对象。The object that uses the GCHandle.

type
GCHandleType

GCHandleType 值之一,指示要创建的 GCHandle 的类型。One of the GCHandleType values, indicating the type of GCHandle to create.

Returns

GCHandle

指定的类型的新 GCHandleA new GCHandle of the specified type. 当不再需要 GCHandle 时,必须通过 Free() 将其释放。This GCHandle must be released with Free() when it is no longer needed.

Attributes

Exceptions

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。An instance with nonprimitive (non-blittable) members cannot be pinned.

See also

Applies to