GCHandle.Alloc 方法

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

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);

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

[<System.Security.SecurityCritical>]
static member Alloc : obj -> System.Runtime.InteropServices.GCHandle

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

Public Shared Function Alloc (value As Object) As GCHandle

參數

傳回

一個 GCHandle 能保護物件免於垃圾回收的新裝置。 GCHandle當不再需要時，必須隨Free()之解除。

屬性

SecurityCriticalAttribute

範例

以下範例展示了 App 一個類別，該類別使用 該方法建立一個 handle 到 受 GCHandle.Alloc 管理物件，阻止該受管理物件被收集。 呼叫該 EnumWindows 方法會傳遞代理（deleged）和受管理物件（兩者皆宣告為受管理型別，但未顯示），並將 handle 投射為 IntPtr。 未管理函式會將型別作為回調函式的參數傳回呼叫者。

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 handle 是不透明的，意思是你無法透過handle解析其所包含物件的位址。

另請參閱

• GCHandleType

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

來源:

GCHandle.cs

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);

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

[<System.Security.SecurityCritical>]
static member Alloc : obj * System.Runtime.InteropServices.GCHandleType -> System.Runtime.InteropServices.GCHandle

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

傳回

一個指定類型的新機 GCHandle 。 GCHandle當不再需要時，必須隨Free()之解除。

屬性

SecurityCriticalAttribute

例外狀況

另請參閱

• GCHandleType