C# 如何将ComObject强制转换为ENVDTE.Project？

我正在使用以下代码：

Object projObj = htProjects[selectedNode]; // htProjects is a Hashtable:key-project Name,value-ENVDTE.Project
Project selectedProject = (Project)projObj; 

我得到以下错误：

Unable to cast COM object of type 'System.__ComObject' to interface type 'EnvDTE.Project'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{866311E6-C887-4143-9833-645F5B93F6F1}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

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我试着注册了前面提到的DLL，但似乎还有其他问题。

找到了解决方案。某些哈希表条目将ENVDTE.ProjectItems作为值。所以需要检查一下

代码：

        if (projObj is Project)
        {
            Project selectedProject = (Project)projObj;
            MessageBox.Show(selectedProject.FullName);
        }
        else if(projObj is ProjectItem)
        {
            ProjectItem selectedProject = (ProjectItem)projObj;
            MessageBox.Show(selectedProject.get_FileNames(1));
        }