如何使用IDispatch.Invoke调用接收浮点值的函数？

问题描述

我无法使用 IDispatch.Invoke 调用具有浮点参数和浮点结果的函数。

I'm having trouble calling a function that has a floating point argument and a floating point result, using IDispatch.Invoke.

这是最小的复制品：

#include <atlbase.h>
#include <comutil.h>

int main(int argc, char* argv[])
{
    CoInitialize(NULL);
    CComPtr<IDispatch> wordapp;
    if (SUCCEEDED(wordapp.CoCreateInstance(L"Word.Application", NULL, CLSCTX_LOCAL_SERVER)))
    {
        CComVariant result;
        CComVariant centimeters((float)2.0);
        CComVariant retval = wordapp.Invoke1(L"CentimetersToPoints", &centimeters, &result);
    }
    return 0;
}

我使用ATL CComPtr 使事情更清洁。但是它是 IDispatch.Invoke 的一个非常松散的包装。

I'm using the ATL CComPtr to make things cleaner. But it's a very loose wrapper around IDispatch.Invoke.

当我运行这个，调用 Invoke1 失败并返回 E_FAIL 。

When I run this, the call to Invoke1 fails and returns E_FAIL.

我怀疑与使用浮点参数和/或返回值相关。如果我调用一个不使用这样的值的函数，调用成功：

I suspect that the problem is related to the use of floating point arguments and/or return value. If I call a function that does not use such values, the invoke succeeds:

CComVariant retval = wordapp.Invoke0(L"ProductCode", &result);

我注意到如果我从VBS或PowerShell调用函数，它会成功。我假设他们都使用晚绑定 IDispatch ，这样就表明我试图至少是可能的。

I note that if I call the function from VBS, or from PowerShell, it succeeds. I'm presuming that they both use late bound IDispatch and so that would indicate that what I am attempting is at least possible.

那么，如何使用 IDispatch 调用此函数？

So, how can I call this function using IDispatch?

推荐答案

好吧，这是一个头脑。这个方法的文档是非常误导，它不是一种方法。它的行为更像一个索引属性，需要DISPATCH_METHOD | DISPATCH_PROPERTYGET标记。 CComPtr不支持，你需要手动旋转。此代码工作：

Well, that was a head-scratcher. The documentation for this "method" is very misleading, it is not a method. It behaves more like an indexed property and requires the DISPATCH_METHOD | DISPATCH_PROPERTYGET flags. CComPtr doesn't support that, you'll need to spin this by hand. This code worked:

    CComVariant result;
    CComVariant centimeters((float)2.0);
    DISPID dispid;
    LPOLESTR name = L"CentimetersToPoints";
    HRESULT hr = wordapp->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT, &dispid);
    assert(SUCCEEDED(hr));

    DISPPARAMS dispparams = { &centimeters, NULL, 1, 0};
    hr = wordapp->Invoke(dispid, IID_NULL, LOCALE_USER_DEFAULT,
            DISPATCH_METHOD | DISPATCH_PROPERTYGET, &dispparams, &result, nullptr, nullptr);
    assert(SUCCEEDED(hr));

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