My Blackberry 10 Cascades (C++, Qt & QML) sample app is crashing on startup with the following error

Question

I am trying to make a sample Blackberry 10 Cascades app in C++, Qt, & QML in the QNX Momentics IDE, and run it in the Blackberry 10 Dev Alpha Simulator. When I start running it, I get the following error messages:

ApplicationPrivate::declarativeEngine: ERROR called from non-UI thread QThread(0x8067e48) ApplicationPrivate::declarativeEngine: Method called from non-UI thread

I have tried googling those error messages - but I only find a few links that actually apply to my situation - and the solutions for those problems don't seem to apply to me.

I know it's got something to do with me trying to call different classes from different qml documents. (Which is something I was having trouble with before - which is why I made this sample app in the first place - to see if I could figure out how to call different classes from different qml documents).

Here is the code of my sample app. There are 7 files (main.qml, main.cpp, app.cpp, app.hpp, Page2.cpp, Page2.h, Page2.qml). I would much appreciate if anyone could help me solve this - because I am not really sure what I am doing wrong.

Thank you.

(I have taken out main.cpp & reduced the code from the other 6 files to what I think are the key parts to this problem).

I know the problem has something to do with my Page2 class and the Page2.qml file.

(I think the problem is that there is something I have to do to be able to call qt code from more than one qml files - and I just don't know what that is).

main.qml:

import bb.cascades 1.0

//-- create one page with a label and text
Page {
    content: Container {
        Button {
            text: "Page 2"
            onClicked: app.goToPage2
        }
    }
}

from app.cpp

App::App()
{
    qmlRegisterType<App>("GDLiteBB", 1, 0, "app");
    qmlRegisterType<Page2>("GDLiteBB", 1, 0, "Page2");

    QmlDocument *qml = QmlDocument::create("main.qml");
    qml->setContextProperty("app", this);

    AbstractPane *root = qml->createRootNode<AbstractPane>();
    Application::setScene(root);
}

void App::goToPage2() {
    Page2::getInstance();
}

from app.hpp

class App : public QObject
{
    Q_OBJECT
public:
    App();

    Q_INVOKABLE void goToPage2();
};

Page2.cpp

QmlDocument * Page2::qml_ = QmlDocument::create("Page2.qml");
AbstractPane * Page2::root_ = qml_->createRootNode<AbstractPane>();
Label * Page2::label_ = root_->findChild<Label *>("label");

Page2::Page2() : QObject() {
    ++count_;
    page2_ = this;
    qml_->setContextProperty("Page2", this);
    Application::setScene(root_);
}

Page2 *Page2::getInstance() {
    return page2_ ? page2_ : new Page2();
}

void Page2::setLabel() {
    label_->setText("This is page 2");
}

Page2.h

class Page2 : public QObject {
    Q_OBJECT

    static Page2 *page2_;
    static unsigned int count_;

    static bb::cascades::QmlDocument *qml_;
    static bb::cascades::AbstractPane *root_;
    static bb::cascades::Label *label_;

    Page2();
public:
    static Page2 *getInstance();
    virtual ~Page2();

    Q_INVOKABLE void setLabel();
};

Page2.qml

import bb.cascades 1.0
import GDLiteBB 1.0

Page {
    content: Container {
        Button {
            text: "Set Label"
            onClicked: Page2.setLabel()
        }
        Label {
            objectName: "Label"
        }
    }
}

Please try to simplify your code until either the error goes away, or it's a minimal example that still reproduces your problem. Nobody here will want to read all the code sections that are irrelevant for the problem. — mic_e
Mic_e => I have taken out main.cpp & reduced the code from the other 6 files to what I think are the key parts to this problem. — user1296259

E.M. E.M. · Accepted Answer · 2013-04-11T18:32:42

I think your problem is these lines:

QmlDocument * Page2::qml_ = QmlDocument::create("Page2.qml");
AbstractPane * Page2::root_ = qml_->createRootNode<AbstractPane>();
Label * Page2::label_ = root_->findChild<Label *>("label");

These objects are being created as soon as the application code loads into memory, which means that it's happening before the event loop starts in main(). All classes that inherit from QObject need to be created after the event loop starts and destroyed before the event loop ends.

My Blackberry 10 Cascades (C++, Qt & QML) sample app is crashing on startup with the following error

1 Answers