Can a Qt 5 project invoke a Qt 4 project? - qt

I have built a UI application using Qt 5.7 and an independent widget using Qt 4.8. The widget uses QGIS API, which is incompatible with Qt5. Is there a way to run the widget from the Qt5 based application?

It cant, the Binary Compatibility of Qt5 means that a library build with Qt 4.8 will not run on it. The Api Compatibility was mostly kept, so if you could compile the QGIS on Qt5, then you could run your application on it.

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An installer for Qt apps

I've created a Qt calculator app using Qt Creator 3.6.0 purely in C++ code (I didn't use Designer)
I would like to know how to use Qt to make it installable for publishing.
I ran the app in both Release and Debug modes and have both folders of the two.
I also downloaded and installed Qt Installer Framework Opensource 2.0.1 for my Qt Creator 3.6.0 (the IDE I use for Qt).
And I also have the .dll files needed to run the .exe file.
I've searched the Web for it. But since I'm a novice in Qt I can't do the works properly, or I don't understand. (They seem complicated)
Now, is there any straight forward method to use an installer for the app to make as platform independent as possible?
If so, what installer? And how to do the process? This is the first time for me.

How to write code for GUI designed in independent Qt designer using Qt creator?

I have a manjaro Linux system. It comes preinstalled with a Qt designer software that has more widgets compared to default Qt creator. But I can only design GUI with this designer software. How would I write code for it?
I have Qt Creator 5.5 installed, but I don't know if it it possible to integrate these two and if yes, how?

Is porting QML based app easy to Windows Phone?

On the qt-project web-site there're available sources as for porting QML to iOS, Android.
http://qt-project.org/doc/qt-5/portingtoandroid.html
http://qt-project.org/doc/qt-5/porting-to-ios.html
It appears to be easy.
Is it so for Windows Phone as well?
Is it so for any other platform?
Qt Project has a Qt for WinRT tutorial providing a step-by-step process to build applications for Windows 8 based devices. Basically to resume the tutorial :
You need the appropriate windows runtime
You may have to build Qt from source for that runtime library
You develop and compile Qt as you would do for a desktop app
You have an additional step for packaging the application.

How to build KDE Oxygen plugin on Qt 5?

I'm moving my project from Qt 4.8.4 to Qt 5.1. On all platforms application looks native except (ironic) KDE. I know problem source - KDE oxygen style (plugin) is compiled on Qt 4.8.4 so it can't be used by Qt 5.1 . So if it is plugin problem only, then maybe building it on Qt 5.1 solve problem. I downloaded KDE Workspace module from KDE which include oxygen source. It is in <kde workspace src>/libs/oxygen but have no idea how to compile only just this little lib. Is anyone have oxygen plugin compiled on Qt 5.1 or know steps how to build it?

A qt5 simple app doesn't run in windows 7

I use Qt 5.0.1 and Qt Creator 2.6.2 in W7. I tried to run a simple app from examples which contains only a window ("Widgets tutorial - creating a window"). When I run it in Qt Creator, it works. But when I run it as a standalone app (Release), it doesn't.
I filled the folder with every dll it had asked (26 MB of dlls, while the app is 10KB!!!). Now it doesn't ask for any files, it just doesn't run at all with no explanations.
I tried to add some files as it is advised in Application deployed with QT5 libraries does not start on Windows 7
but no luck. In
HelloWorld Deployment with QtQuick 2.0 in Windows 7 and XP
there are no problems in w7.
May be this a dependency problem, These links describes it:
Qt 5.0 program runs in QtCreator but not outside
How to build QTcore4.dll without dependency to MSVCx80.dll?
platforms/qwindows.dll is a "non-required" required DLL to run Qt5 apps. Build your app in Release mode and steal the DLL from Qt Creator's folder (or find it into Qt's bin/platforms folder)

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