Can't make my QML rectangle plugin appear.....

  • Using a library template I did the following:

    my .pro file:

    TEMPLATE = lib
    TARGET = plug
    QT += qml quick
    CONFIG += qt plugin c++11
    TARGET = $$qtLibraryTarget($$TARGET)
    uri = com.afmx.rndtngl
    # Input
    SOURCES += \
        plug_plugin.cpp \
    HEADERS += \
        plug_plugin.h \
    DISTFILES = qmldir \
    !equals(_PRO_FILE_PWD_, $$OUT_PWD) { = $$OUT_PWD/qmldir
        copy_qmldir.depends = $$_PRO_FILE_PWD_/qmldir
        copy_qmldir.commands = $(COPY_FILE) \"$$replace(copy_qmldir.depends, /, $$QMAKE_DIR_SEP)\" \"$$replace(, /, $$QMAKE_DIR_SEP)\"
        QMAKE_EXTRA_TARGETS += copy_qmldir
        PRE_TARGETDEPS += $$
    qmldir.files = qmldir
    unix {
        installPath = $$[QT_INSTALL_QML]/$$replace(uri, \\., /)
        qmldir.path = $$installPath
        target.path = $$installPath
        INSTALLS += target qmldir

    The usual C++ files for plugin definition:

    plugin.h && plugin.cpp:

    #ifndef PLUG_PLUGIN_H
    #define PLUG_PLUGIN_H
    #include <QQmlExtensionPlugin>
    class PlugPlugin : public QQmlExtensionPlugin
        Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QQmlExtensionInterface")
        void registerTypes(const char *uri);
    #endif // PLUG_PLUGIN_H
    #include "plug_plugin.h"
    #include "roundtangle.h"
    #include <qqml.h>
    void PlugPlugin::registerTypes(const char *uri)
        // @uri com.afmx.rndtngl
        qmlRegisterType<RoundTangle>(uri, 1, 0, "RoundTangle");

    The C++ description of the Object, roundtangle.cpp & roundtangle.h:

    #ifndef ROUNDTANGLE_H
    #define ROUNDTANGLE_H
    #include <QObject>
    class RoundTangle : public QObject
        RoundTangle(QObject *parent = 0);
    #endif // ROUNDTANGLE_H
    #include "roundtangle.h"
    #include <QDebug>
    RoundTangle::RoundTangle(QObject *parent):
        // By default, QQuickItem does not draw anything. If you subclass
        // QQuickItem to create a visual item, you will need to uncomment the
        // following line and re-implement updatePaintNode()
        // setFlag(ItemHasContents, true);
        qDebug()<<"Ok soo here we go.....";

    The Round tangle QML definition:

    import QtQuick 2.0
    Rectangle {
        Component.onCompleted: {

    I go to the build dir, and type:

    > make clean
    > make install

    A lot of compiling goes in here..... but everything is ok and the .dylib and qmldir files are copied to the Qt com/afmx/rndtngl

    mac$ ls -la /Users/xxx/Code/Qt55/5.7/clang_64/qml/com/afmx/rndtngl/
    total 176
    drwxr-xr-x  4 xxx  staff    136 Sep  8 10:22 .
    drwxr-xr-x  4 xxx  staff    136 Sep  8 05:32 ..
    -rwxr-xr-x  1 xxx  staff  82012 Sep  8 10:22 libplug_debug.dylib
    -rw-r--r--  1 xxx  staff     37 Sep  8 10:02 qmldir

    And of course in another Qt Quick Application project, I try to use RoundTangle:

    Heres the .pro:

    TEMPLATE = app
    QT += qml quick
    CONFIG += c++11
    SOURCES += main.cpp
    RESOURCES += qml.qrc
    # Additional import path used to resolve QML modules in Qt Creator's code model
    QML_IMPORT_PATH = /Users/xxx/Code/hack/QtApps/qqplugin/plug/plug
    # Default rules for deployment.

    Heres the main.qml:

    import QtQuick 2.6
    import QtQuick.Window 2.2
    import com.afmx.rndtngl 1.0
    Window {
        visible: true

    The Syntax highlighting recognizes the shared lib in the Qt installation, so it colorizes fine. I run, and the constructor displays the message in it but no rectangle is displayed. It's like the C++ Object is load in memory, but QML RoudTangle definition is not......

    What Am I doing wrong... I know this is extense but help me here please!

  • @Julian-Guarin

    You do not seem to have any code on your custom class. Do you see your debug output («so here we go...») when you run your application?

  • Moderators

    you have some misunderstanding i guess.
    You defined your RoundRectangle type in QML and C++. But you need to decide either or.
    Currently you registered your C++ implementation, which actually is jsut a plain QObject which doesn't draw anything.
    Your QML implementation would do would you want, but you need to add it to the qrc of your plugin and specify it in a qmldir file for example.

  • @t3685 Yes!. Indeed that is what flashes on the console.

  • @raven-worx That's It's what I've figured. I guess there's something I don't understand. What I mean is How Do I get to use a QML, like it is "installed" inside the Qt57/qml/com/whateever/qmliwantoreuse?.

    How would I reuse a QML without having to copy it from project to project? Just like the QtQuicks objects... that's what i'm trying to achieve here....

    Thank you...

  • Moderators

    id you are just using qml files you do not necessarily have to create a plugin. Since Qt is able to load qml files directly from the filesystem.
    But if you want you can do this:

    1. put the qml file in qrc (e.g. myresources.qrc) of the plugin
    2. add Q_INIT_RESOURCE(myresources); in the constructor of the plugin class
    3. put a qmldir file next to your plugin with the following content:
    module MyModuleName
    plugin myquickplugin
    RoundTangle 1.0 qrc:///path/to/1.0/RoundTangle.qml

  • @Julian-Guarin

    You have no painting logic for your rectangle. That would explain why you do not see anyting.

  • @t3685 Yes, Im trying it by using a QML file which invokes QtQuick and a Rectangle.... isn't that possible?

  • @Julian-Guarin

    Like @raven-worx, it is unclear what you are tyring to do? Are you making a custom C++ class to use in your QML or are you making a QML file?

  • @t3685 I guess it is. Sorry about that.

    What I'm trying to achieve is to redirect qDebug message functions to a overlaid rectangle, on my QML UI. For the matter I set two goals:

    1. Draw a semi transparent Rectangle with a ListView a ListModel and a Delegate, which propagate mouse events to the rest of the QML objects, and display debug messages. (Using a QML File)
    2. Redirect the qDebug() using QLogMessage functions and stuff which emit signals with the message and message's color to the overlaid rectangle (C++)

    So I said, let's use the plugin C++ QtQuick2 project template, and for the C++ part it worked all right, what did not work is the QML.

    It is like the QML file is not used when compiling the C++ portion, in fact when I " make |grep '.qml' ", there's no line associated, so no qml file is being used.

    So I decided to make a separated file for the QML (view) apart from the C++ portion (controller)...

    The link to the project is the following:

  • @Julian-Guarin @t365 @raven-worx

    Making things apart seemed to work:

    Only use the plugin for instantiate the C++ portion of what I want to achieve.

    The overlaid rectangle, was done in a different QML file. And the QML file was

    manually copied to the Qt55/5.7/clang_64/qml/com/afmx/debug, where all the QML dynamic modules live.

    The QML copying it's annoying, and non functional, I will try to automate with the .pro file.... am I right on that one?

    So this now works:

    ApplicationWindow {
        visible: true
        width: 800
        height: 600
        title: qsTr("Debug")
        Rectangle {
            anchors.fill: parent
                anchors.fill: parent
                onClicked: console.log("Ok dokey");
            onDebugMessage: dbgConsole.debugViewAdd(aString,aColor)

    AFMXDebugScreenConsole is the QML file with the overlaid rectangle and AFMXDebug is the C++ messages redirection object.

    I guess it makes sense, because of controller/view isolation. But to have to copy this manually into your Qt installation is not that technical...

    Is there (I guess, should be) a better way to achieve this?.

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