Extend Qlable Widget and add it to the QDesigner Widgetlist

  • Hallo, I'm trying to subclass QLable and add some functionality to the new class. This works well, but now I want my new Widget to show up in the QT Designer. Im using QT5 and read some Tutorials for creating Plugins, but I didn't understand all off that. is there a simple solution for my problem.
    Thank you very much for your help

  • Moderators

    [quote author="M001" date="1375813969"]Im using QT5 and read some Tutorials for creating Plugins, but I didn’t understand all off that. is there a simple solution for my problem.[/quote]

    What have you done so far? What is exactly not working? Did you read "this":http://qt-project.org/doc/qt-5.0/qtdesigner/customwidgetplugin.html tutorial? It should be actually really straight forward...
    But there are some pitfalls when creating plugins which lead to fail "silently":http://canvoki.net/Codders/qtpluginnotloading.html when they are loaded.

    But this is all guessing, since you were very vague with the description about your problem...

  • hey :), I also tryed the "Custom Widget Plugin Example" that you mentioned. I copied all the Files from the Website to my computer and open them with QT5.1 and press compile (release). I get the customwidgetplugin.dll and copied it to the plugin directory C:\Qt\Qt5.1.0\5.1.0\mingw48_32\plugins\designer. Then I restart QT, but the Plugin wasn't added, and when I open *Tools>Formulareditor>about QT Designer Plugins * it's also not there. I thougt if i copy a codeexample from qt-project website it should work :), but it dosend. So I think there where no missspelling and theses kinds of errors. There must be another error.
    I am using:
    Qt Creator 2.7.2
    Based on Qt 5.1.0 (32 bit)
    Created on Jul 2 2013 um 20:48:03
    Revision ea5aa79dca

    on a 64bit Windows 7 installation

  • Moderators

    did you look into the second link in my post?

    Qt plugin system has a version check built in.
    My guess: Since you built your plugin with Qt 5.1 it can only be loaded by applications also built with Qt 5.1 (or higher).
    But if the application is built with Qt 5.1.x and the plugin with Qt 5.0.x it should work AFAIK. (backward compatibility)

  • I compiled the plugin with my QT5.1 installation and want to uses the plugin in the same QT5.1 installation. I thougt this should be working.

  • Moderators

    QtDesigner needs to be compiled with the same Qt version number (or higher). If it is, there must be another problem.

  • okay thanks :), I have checkt the Versions of Creator and designer and they all are based on QT5.1. So when I checkt the Version number ob QTDesigner I opend it from the Startmenu and not via QTCreator and the analogclock plugin is in the Widgetbox and I could use ist in my main window :D. But here is my next question, are the QTDesigner opend from QTCreator and the QTDesigner opend from Startmenue two different Programms, with two different plugin directorys or why I can't find my plugin in one of them but not in the other? Tank you very much for your Help raven-worx :)

  • There are two differnt folders. I copied it in the folder for the creator C:\Qt\Qt5.1.0\Tools\QtCreator\bin\plugins\designer. And now the plugin is showing up, but there is an error message:
    ... .dll coulnd't be load. The procedure could not be found
    why do I get this error in Creator, when I don't get this error with the same File in QTDesigner?

  • Lifetime Qt Champion

    I think you are hit by the problem described "here":http://qt-project.org/doc/qtcreator-2.8/adding-plugins.html#matching-build-keys

  • i downloaded "Qt 5.1.0 for Windows 32-bit (MinGW 4.8, OpenGL, 666 MB)" it is compiled with MinGW 4.8. Thats the version I currently use, it was installed by the setup. I'm using:
    Qt Creator 2.7.2
    Based on Qt 5.1.0 (32 bit)
    Created on Jul 2 2013 um 20:48:03
    Revision ea5aa79dca

    I saw that there is a new QTCreator Version avaliabel "Qt Creator 2.8.0 for Windows (52 MB) ". But how do i find the information with wich version of MinGW it is compiled?

  • so, i have installed "qt-windows-opensource-5.0.2-mingw47_32-x86-offline.exe" and copied the Plugin created with “Qt 5.1.0 for Windows 32-bit (MinGW 4.8, OpenGL, 666 MB)” into the plugin folder of QT5.0.2 QT Creator. Now I get anothe error message when I open the "About QT Creator Plugins" Dialog: ... .dll uses an incompatible QT-libary. (5.1.0) [release]. I found a link where this problem is described: "http://harmattan-dev.nokia.com/docs/library/html/qt4/deployment-plugins.html":http://harmattan-dev.nokia.com/docs/library/html/qt4/deployment-plugins.html . I can't use the Plugin created with 5.1 in 5.0 thats okay, but using the pluigin created with 5.1 in QT5.1 should be okay, but it doesn't work. I don't know what's going on here :(

  • Lifetime Qt Champion

    From the link I posted, QtCreator from the SDK is built with MSVC so you need to recompile QtCreator to use your plugin or use the MSVC build (then you would need to install Visual Studio)

  • another step forward :), Thanks SGaist!
    I downloaded "Qt 5.1.0 for Windows 32-bit (VS 2012, 511 MB)" compiled the Plugin with this Version and copied the .dll to the "Qt 5.1.0 for Windows 32-bit (MinGW 4.8, OpenGL, 666 MB)" installation Plugin folder and now I could use this Plugin in my "Qt 5.1.0 for Windows 32-bit (MinGW 4.8, OpenGL, 666 MB)" installation. That means i see ist in QTCreator-Designer and could move it on my mainwindow. But when i try to compile my project I get these errors:

    C:\Users\name\build-TestPlugIns-Desktop_Qt_5_1_0_MinGW_32bit-Debug\ui_mainwindow.h:18: Fehler:analogclock.h: No such file or directory

    the headerfile is missing. I thougt this information is all built in the .dll file?

    Edit: I am using MS Visual Studio 2012

  • Lifetime Qt Champion

    The header is needed to write your code like for any other library

  • sorry for this stupid question, but what should i write into the headerfile?

  • Lifetime Qt Champion

    It's the header file of your widget from the plugin

  • Moderators

    [quote author="M001" date="1375882194"]I thougt this information is all built in the .dll file?[/quote]
    It is but only the implementation. To use it you need the header file just for the compiler to know which interface to use. The linker then looks for the implementation either in your binary or like in your case in the plugin (dependency).

  • okay i include the headerfile and get many errors:

    ...ui_widget.h:56: Fehler:undefined reference to `_imp___ZN11AnalogClockC1EP7QWidget'...moc_analogclock.cpp:70:

    ...moc_analogclock.cpp:70: Fehler:undefined reference to `_imp___ZN11AnalogClock16staticMetaObjectE'

    ...moc_analogclock.cpp:65: Fehler:undefined reference to `_imp___ZN11AnalogClock16staticMetaObjectE'

  • a little bit more information:

    the first error is caused by here:

    file: ui_widget.h
    class Ui_Widget
    AnalogClock *analogClock;

    void setupUi(QWidget *Widget)
        if (Widget->objectName().isEmpty())
        Widget->resize(400, 300);
        analogClock = new AnalogClock(Widget); //this line produces the error
        analogClock->setGeometry(QRect(60, 60, 199, 151));
    } // setupUi
    void retranslateUi(QWidget *Widget)
        Widget->setWindowTitle(QApplication::translate("Widget", "Widget", 0));

    #ifndef QT_NO_TOOLTIP
    analogClock->setToolTip(QApplication::translate("Widget", "The current time", 0));
    #endif // QT_NO_TOOLTIP
    #ifndef QT_NO_WHATSTHIS
    analogClock->setWhatsThis(QApplication::translate("Widget", "The analog clock widget displays the current time.", 0));
    #endif // QT_NO_WHATSTHIS
    } // retranslateUi


    second error:

    file: moc_analogclock.cpp

    const QMetaObject *AnalogClock::metaObject() const
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;

    file: --moc_analogclock.cpp

    const QMetaObject AnalogClock::staticMetaObject = {
    { &QWidget::staticMetaObject, qt_meta_stringdata_AnalogClock.data,
    qt_meta_data_AnalogClock, qt_static_metacall, 0, 0}

  • if I add analogclock.h and analogclock.cpp files the code compiles and I could use my plugin. but i thougt the analogclock.cpp should be inside the .dll file. Why do I have to add the analogclock.cpp file?

  • did you progress any further on this topic i am stuck at the same spot as you were then please help if you found a solution

  • how this stuffs work:

    1. custom plugin dll in i.e. ..\qtcreator-2.8.0\bin\plugins\designer\ is loaded by the QtCreator and it needs no header file or other information

      the plugin's interface provides an includeFile() by which the designer knows what header has to include in ui header file generated for your project

    2. what follows is just an exemplification:

    • copy customwidgetplugin.dll and customwidgetplugin.lib to i.e ...\Qt\4.8.5\plugins\designer\

    • add the header file of your custom widget i.e. analogclock.h in your application dir in order to be found at compilation from ui header file

    -in pro file add the export library file .lib,


    LIBS += $$(QTDIR)\plugins\designer\customwidgetplugin.lib

    I have tested and works


  • but mine is still not working i have added the library but whenever i run after adding the library the application starts and terminates unexpectedly without showing any error

  • hehe ... you mix debug and release app and plugin dll, or conversely

    try to compile both for release or debug

  • i have only used release files do i need to use debug files as well somewhere

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