我的Blackberry 10 Cascades（C ++，Qt和QML）示例应用程序在启动时崩溃，并出现以下错误

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"
        }
    }
}

Answer 1

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.