将本地指针转换为C ++ \CLI手动对象引用？ [英] Cast native pointer to a C++\CLI manged object reference?

问题描述

我有一个通过委托调用的回调。在其内部，我将需要处理从记录过程到达的缓冲区数据。 Normaly在非托管上下文中，我可以对dwParam1执行reinterpret_cast以获取对象引用。
但是在一个被管理的上下文中，如何将一个DWORD_PTR转换为受管对象ref？

I have a callback that is called through a delegate. Inside it I will need to treat the buffer data that arrive from a record procedure. Normaly in a unmanaged context I could do a reinterpret_cast on dwParam1 to get the object reference. But in a manged context how can I cast a DWORD_PTR to a managed object ref?

    static void WaveInProc(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2) 
    {
        ControlLib::SoundDevice^ soudDevice = ?cast_native2managed?(dwParam1);

推荐答案

这里ya go，或多或少gcroot我的注释上面）：

Here ya go, more or less what gcroot (per my comment above) does:

using namespace System;
using namespace System::Runtime::InteropServices;

// track an object by a normal (not pinned) handle, encoded in a DWORD_PTR
DWORD_PTR ParamFromObject(Object^ obj)
{
    return reinterpret_cast<DWORD_PTR>(GCHandle::ToIntPtr(GCHandle::Alloc(obj)).ToPointer());
}

static void WaveInProc(PVOID hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2) 
{
    // unwrap the encoded handle...
    GCHandle h = GCHandle::FromIntPtr(IntPtr(reinterpret_cast<void*>(dwParam1)));
    try
    {
        // and cast your object back out
        SoundDevice^ x = safe_cast<SoundDevice^>(h.Target);
    }
    finally
    {
        // remember to free the handle when you're done, otherwise your object will never be collected
        GCHandle::Free(h);
    }
}

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