[Interest] QML ApplicationWindow fails to open a window

[Juan Navarro]

Oh My God, that's a shameful way of doing a first post. Obviously, my
QQmlApplicationEngine is getting destroyed after falling outside the
scope of MainWindow destructor. Glad nobody read this, right? :-) I
guess today's being a bad day already. Sorry for the noise!

On Mon, May 26, 2014 at 4:06 PM, Juan Navarro <oneorjuan at gmail.com> wrote:
> Sorry I forgot to indicate that I'm using latest Qt release, installed
> from the official Qt 5.3 online installer, using Ubuntu 14.04.
>
> On Mon, May 26, 2014 at 4:04 PM, Juan Navarro <oneorjuan at gmail.com> wrote:
>> Hi there;
>> i'm struggling with the behavior of ApplicationWindow and I found that
>> it only opens a window when used directly from main() but not from a
>> custom class. Let's explain with an example:
>>
>> ----
>> main.qml:
>>     import QtQuick 2.2
>>     import QtQuick.Controls 1.1
>>
>>     ApplicationWindow {
>>         visible: true
>>         width: 640
>>         height: 480
>>
>>         Text {
>>             text: "Hello World"
>>             anchors.centerIn: parent
>>         }
>>     }
>> ----
>> main.cpp:
>>     #include <QApplication>
>>     #include <QGuiApplication>
>>     #include <QQmlApplicationEngine>
>>     #include <QObject>
>>     #include <QWidget>
>>     #include <QUrl>
>>
>>     class MainWindow1
>>     {
>>     public:
>>         MainWindow1()
>>         { QQmlApplicationEngine engine("main.qml"); }
>>     };
>>
>>     class MainWindow2 : public QObject
>>     {
>>     public:
>>         MainWindow2(QObject* parent = 0)
>>             : QObject(parent)
>>         { QQmlApplicationEngine engine("main.qml"); }
>>     };
>>
>>     class MainWindow3 : public QWidget
>>     {
>>     public:
>>         MainWindow3(QWidget* parent = 0, Qt::WindowFlags flags = 0)
>>             : QWidget(parent, flags)
>>         { QQmlApplicationEngine engine("main.qml"); }
>>     };
>>
>>     int main(int argc, char *argv[])
>>     {
>>         QApplication app(argc, argv);
>>
>>     //    MainWindow1 window;
>>     //    MainWindow2 window;
>>     //    MainWindow3 window;
>>         QQmlApplicationEngine engine("main.qml");
>>
>>         return app.exec();
>>     }
>> ----
>>
>> Check the main() function: only with the uncommented code I get to see
>> a new Window which shows the "Hello World" text. If we comment that
>> and uncomment any of the other 3 options, which use a custom
>> "MainWindow" class, then nothing will come out. I derived MainWindow
>> from QObject and QWidget in hopes to find some solution, but I
>> actually would think that a standalone MainWindow class should suffice
>> for this basic usage scenario.
>>
>> Is it a bug or I am misusing this class?
>>
>> Also, extracting the inner QQuickWindow and forcing a call to show()
>> doesn't work; ie:
>>     MainWindow1()
>>     {
>>         QQmlApplicationEngine engine("main.qml");
>>         Q_ASSERT(engine.rootObjects().size() > 0);
>>         QQuickWindow* window =
>> qobject_cast<QQuickWindow*>(engine.rootObjects().at(0));
>>         window->show();
>>     }
>> doesn't work.