[Qt-interest] plugin fails to load with uresolved links to another plugin

[Andreas Pakulat]

On 16.06.10 18:07:55, Kishore wrote:
> On Wednesday 16 Jun 2010 5:36:30 pm Thiago Macieira wrote:
> > Em Quarta-feira 16 Junho 2010, às 13:51:58, Kishore escreveu:
> > > like with many other applications is that plugin A depends on
> > > plugin B.
> > 
> > That is not a normal situation.
> > 
> > Plugins don't depend on each other. That's why they are called "plugins".
> > 
> > Something that can be depend on is called "library". You link to it and the
> > system will automatically load it.
> > 
> > > Now, everything works fine if i declare that plugin A depends on B using
> > > the TARGET_LINK_LIBRARIES() (I use the CMake build system) function. But
> > > for this to work, i have to declare both A and B as SHARED instead of
> > > MODULE libraries.
> > 
> > That's what the effect of what I said above.
> 
> That is what i was told by Andreas too in the other list. Perhaps i 
> misunderstand this post too http://labs.trolltech.com/blogs/2010/04/29/best-
> practices-when-implementing-iplugin-methods/
> 
> Does this mean that plugin A (the dependent) cannot call API in plugin B? I am 
> confused since several posts on the net seem to suggest that this is possible.

Right, you can only call functions from shared libraries, not from other
plugins. One of the main points of having plugins is to be able to exchange
them, this means that a certain plugin A must not have a direct dependency
on the API or implementing of a plugin B. 

Dependencies between plugins are usually expressed by using pure virtual
classes declared in a header-only way. This way plugin A doesn't need to
link against anything to be able to use the interface. The second piece is
a central library that manages all loaded plugins and allows plugin A to
retrieve a pointer to a plugin that implements the given interface. Then
you can call the methods on the interface from plugin A without having to
care wether its plugin B, E or Q implementing that interface.

Andreas

-- 
Don't get to bragging.