[Interest] Doubt extending my app functions ability

Bob Hood bhood2 at comcast.net
Fri Jan 13 16:08:22 CET 2017

On 1/12/2017 4:33 PM, Ernesto wrote:
> Hello again, first, thanks to Bob Hood for his quickly reply.
> I understood your explanation about my second problem, but I have another 
> issue writing your solution in an example project. I have a MainApp (QT 
> Widgets project) and a Lib1 (C++ Static Library project) and here is the code:

If you are creating statically linked plug-ins, that requires a different 
approach.  However, you also mention "the Lib1.dll file" elsewhere, so I 
assume you are not.

I'm sure you have read the online docs about Qt plug-in, Ernesto, but probably 
missed a subtle point which is evident in your interface file:

> //This is header file of my interface, is included by both projects
> classPInterface:publicQObject
> {
> public:
> explicitPInterface(QObject*parent=0);
> virtualQString/Name/()const=0;
> signals:
> publicslots:
> };

You have to designate/declare the class that will be the plug-in interface.  
Try adding the following declarations to your interface file "PInterface", so 
it looks something like this:

     class PInterface : public QObject
         explicit PInterface(QObject *parent = 0);
         virtual QString Name() const = 0;

     public slots:

**    Q_DECLARE_INTERFACE(PInterface , "org.Ernesto.PInterface")**

And try again.

Also, a couple of observations:

 1. Add a virtual destructor to your interface class so destructors of
    subclasses are properly called.
 2. If you'll notice my original code example, I use QPluginLoader to load a
    factory instance.  The Qt plug-in system (QPluginLoader) *does not do
    multiple instancing of plug-ins*.  Therefore, if you will need multiple
    copies of any given plug-in you load, you'll need to use the Factory
    Pattern within each plug-in shared library to generate and return
    instances, and then designate the Factory class interface as the Qt
    plug-in interface instead; e.g.:

     class PInterfaceFactory : public QObject
         virtual PInterface* newInstance() = 0;

     Q_DECLARE_INTERFACE(PInterfaceFactory, "org.Ernesto.PInterfaceFactory")

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20170113/8b97be61/attachment.html>

More information about the Interest mailing list