How to use qmlpreview?

[rudolflovrencic]

@GrecKo Thank you for your response. I haven't been able to make it work - I've made a branch cmake-qml-redirect (link) that starts to implement your suggestion, but I'm getting No qmldir at "/path/to/project/root/" at project build time.

Do you have an example of how that should be set up?

[GrecKo]

Honestly I don't know, I tried to make it work with qmlpreview yesterday after my message to see if it would be simple but I didn't unsterstand much.

I recompiled qmlpreview to add more debug messages but I think I need message on the other side (the qml debug server running in the application) to get the full picture.
The window closed and re-opened itself upon a change but the change was ignored.

I'll ask Qt commercial support about this. For now the manual method with your own QFileSystemWatcher or shortcut seems to be the sensible one.

[GrecKo]

As for your cmake / qmldir issue I'm not sure. I first tried it with a simpler CMake like this:

...
qt_add_executable(appuntitled40
    main.cpp
)

qt_add_qml_module(appuntitled40
    URI untitled40
    VERSION 1.0
    QML_FILES
        Main.qml
)
...

I do use it one a more complicated project with multiple CMakeLists.txt and modules though.

[rudolflovrencic]

@GrecKo Are you able to share main.cpp for such setup? I am blocked on that.

[GrecKo]

@rudolflovrencic just a default generated main.cpp:

#include <QApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.loadFromModule("untitled40", "Main");

    return app.exec();
}

[rudolflovrencic]

@GrecKo Don't you handle key press signals from QML and invoke clearSingletons, clearComponentCache and loadFromModule in main.cpp? That was the impression I got from post #4 where you introduced the enable_qml_hotreload CMake function.

Basically, I'm asking: how do you currently do a hot reload with a key press? Minimal working example or a bit more details would be useful since I'm a bit lost in the advice so far. I'm especially interested in your approach since you said that you maintain the same QML in production and for hot reloading:

@GrecKo said in How to use qmlpreview?:

...but I believe using Loader is not the correct approach since that's different from the production code you want.

In other words, you avoid the QML scaffolding needed for hot reloading (apart from catching the hot reload key press, I guess).

[GrecKo]

@rudolflovrencic Either use a recursive QFileSystemWatcher or a QML Shortcut / c++ eventFilter depending on you want to trigger the reload, then connect that to a function which does the following:

for (QObject* rootObject : m_engine->rootObjects()) {
  rootObject->deleteLater();
}
QMetaObject::invokeMethod(this, [this] {
    m_engine->clearSingletons();
    m_engine->clearComponentCache();
    m_engine->loadFromModule("MyAppModuleUri", "Main");
}, Qt::QueuedConnection);

[Markkyboy]

How are you starting/trying to start QML preview?, I use it when creating desktop apps for Windows 10 and to an extent, for my Android phone.

[rudolflovrencic]

@Markkyboy As I mentioned in the original post, just qmlpreview myexe. The executable myexe is compiled with QML debugging enabled.

[rudolflovrencic]

@GrecKo said in How to use qmlpreview?:

I'll ask Qt commercial support about this.

Did you get a chance to ask them and are there any pointers?