c++ - 将 WPARAM 传递到 DragQueryFile 不兼容？

Question

我有点困惑。当一个文件被拖到一个带有 WS_EX_ACCEPTFILES 标记的窗口上时，它会将一个 PostMessage 放入 WndProc 函数中，该函数将 UINT 消息设置为 WM_DROPFILES，并且根据

https://msdn.microsoft.com/en-us/library/windows/desktop/bb774303(v=vs.85).aspx

WPARAM = (WPARAM) (HDROP) hDrop;所以我是否错误地假设我可以使用 WPARAM 来初始化 HDROP 或只是将它传递到 DragQueryFile ？？

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
switch (message) {
case WM_CREATE:
    return 0;

case WM_DROPFILES:
    TCHAR* FilePath;
    HDROP hDrop = wParam; //wParam cannot be used to ini. an entity of type HDROP
    //HDROP hdrop = (HDROP)wParam; initialization of hDrop is skipped by case label
    DragQueryFile(wParam, 0, FilePath, 0); //wParam not compatible
    return 0;

case WM_DESTROY:
    PostQuitMessage(0);
    return 0;
}
return DefWindowProc(hwnd, message, wParam, lParam);
}

感谢各种帮助。

Answer 1

您需要将 wparam 转换为 HDROP，然后迭代提供缓冲区的丢弃文件路径。

case WM_DROPFILES:
{
    auto const drop_handle{reinterpret_cast< ::HDROP >(wParam)};
    auto const dropped_files_count
    {
        ::DragQueryFileW(drop_handle, 0xFFFFFFFF, nullptr, 0)
    };
    ::std::vector< wchar_t > buffer;
    for(::UINT dropped_file_index{0}; dropped_files_count != dropped_file_index; ++dropped_file_index)
    {
        auto const file_path_symbols_count_excluding_terminating_null
        {
            ::DragQueryFileW(drop_handle, dropped_file_index, nullptr, 0)
        };
        if(0 < file_path_symbols_count_excluding_terminating_null)
        {
            auto const buffer_size{file_path_symbols_count_excluding_terminating_null + 1};
            buffer.resize(buffer_size);
            auto const copied_symbols_count_excluding_terminating_null
            {
                ::DragQueryFileW(drop_handle, dropped_file_index, buffer.data(), buffer_size)
            };
            if(copied_symbols_count_excluding_terminating_null == file_path_symbols_count_excluding_terminating_null)
            {
                buffer.back() = L'\0'; // just in case....
                // buffer now contains file path...
            }
        }
    }
    break;
}

但是请注意，即使处理 WM_DROPFILES 应该有效，处理拖放的首选方法是实现 IDropTarget interface和 register it as drop target handler为您的应用。