There are only two caveats in this case. First, QML files that are to import anything from the library must first import 'MyLib 1.0' before importing anything else ('MyLib.Rectangle', 'MyLib.Circle', etc.). This is so that the plugin is loaded initially to populate the other imports. Secondly, this will produce the following message when the plugin is loaded:
Module 'MyLib' does not contain a module identifier directive - it cannot be protected from external registrations.
However in my case, this is not an issue and can be safely overlooked.
Qt Designer is included in Qt sources and works only for UI files. Qt Creator (the IDE) is a separate application and a separate project. You need to install or compile it first, for example from qt.io/downloads.
Once you have Qt Creator installer, you need to open the settings, add your Qt Version, then add a so called Kit (which is Qt Version + compiler bundle), and then you are ready to go.
If you want to avoid all that hassle, use the Qt installer from the link above - it will install Qt, Qt Creator, and set everything up for you, completely automatically.
While not necessarily recommended, you can use Qt's private API with the limitation that it might disappear in a future version so you're basically tied with the Qt version you build your application against.
As for a solution on how to redirect everything through something else than QAbstractFileEngine, I'd recommend posting that question to the interest mailing list. You'll find there Qt's developers/maintainers. This forum is more user oriented.
Yes, it works if I build a normal shared library an a designer plugin containing the widgets used by other plugins.
The normal shared library is used to be linked to the other ones and the plugin is loaded into the designer to have the widgets available there.
It looks like it is not possible to connect a signal to a signal in the designer. You will need to do this in your code. But I would not do this in ui file! Because next time you use the designer it will be overwritten!
I don't know if there's a way to change the display format of the editor. You can ask the Qt Creator engineers directly (and request the feature to set the editor's format) at the Qt Creator Mailing List: http://lists.qt-project.org/mailman/listinfo/qt-creator . Subscribe to the list and post there.
@ChrisW67 i have tried your solution i have created user class and employee class by extending user class. but i can't access user class widgets. i have defined them as protected. can you show me correct way to do it?