PySide How to see QML errors in python console?

Question

I have the following code:

if __name__ == '__main__':
    os.environ["QT_QUICK_CONTROLS_STYLE"] = "Material"
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()

    engine.load('./QML/main.qml')

    if not engine.rootObjects():
        sys.exit(-1)

    sys.exit(app.exec_())

As you can see, if `engine.load' fails all I'll see is a '-1' exit code, without any elaboration on why it failed and what the error happened. How can I print the QML error in the python console?

There was a walkaround for this with when using QQuickView instead of QQmlApplicationEngine and is described in this post, however, I wonder if the something similar can be achieved for QQmlApplicationEngine?

@eyllanesc I tried to set QQmlEngine::setOutputWarningsToStandardError(bool enabled) to true, and to connect to the warnings signal ... No luck so far... — Curtwagner1984
– Curtwagner1984, Commented Dec 31, 2018 at 22:41
Exactly, you have reviewed stackoverflow.com/questions/45805076/…: this is probably a bug, I recommend you report it. — eyllanesc
– eyllanesc, Commented Dec 31, 2018 at 22:43

eyllanesc · Accepted Answer · 2019-03-16 23:41:46Z

5

If you want to know the error message when using QQmlApplicationEngine you should use the warnings signal but it does not seem to work, so a workaround is to use qInstallMessageHandler to get the messages that Qt gives.

import os
import sys
from PySide2 import QtCore, QtGui, QtQml

def qt_message_handler(mode, context, message):
    if mode == QtCore.QtInfoMsg:
        mode = 'Info'
    elif mode == QtCore.QtWarningMsg:
        mode = 'Warning'
    elif mode == QtCore.QtCriticalMsg:
        mode = 'critical'
    elif mode == QtCore.QtFatalMsg:
        mode = 'fatal'
    else:
        mode = 'Debug'
    print("%s: %s (%s:%d, %s)" % (mode, message, context.file, context.line, context.file))


if __name__ == '__main__':
    os.environ["QT_QUICK_CONTROLS_STYLE"] = "Material"
    QtCore.qInstallMessageHandler(qt_message_handler)
    app = QtGui.QGuiApplication(sys.argv)
    engine = QtQml.QQmlApplicationEngine()
    qml_filename = os.path.join(os.path.dirname(__file__), 'QML/main.qml')
    engine.load(QtCore.QUrl.fromLocalFile(qml_filename))
    if not engine.rootObjects():
        sys.exit(-1)
    sys.exit(app.exec_())

edited Mar 16, 2019 at 23:41

answered Dec 31, 2018 at 23:03

eyllanesc

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10 Comments

Curtwagner1984 Over a year ago

This seems to work when there is an error in the QML files themselves,(For example when I input a string value in a height: parameter) however, it doesn't work when there is a problem in the imports. I made a delegate in another file(In the same directory as 'main.qml') and I'm trying to import it into 'main.qml' this is where my engine.load is failing. Yet it seems that qInstallMessageHandler isn't helpful for this scenario.

eyllanesc Over a year ago

@Curtwagner1984 You could share your test through gist or github.

Curtwagner1984 Over a year ago

@eyllansec Yes, Here it is: gist.github.com/curtwagner1984/c091e4ec262289e2c59e911137d1b5c6

eyllanesc Over a year ago

@Curtwagner1984 Do not you have another simpler example? I do not want to have to get the credentials of reddit to be able to test the problem :-)

Curtwagner1984 Over a year ago

@eyllansec I've changed the main, added a moc sub, also created a new 'qml' file. Right now it exits with code -1 without telling what the error is. I've updated the gist Does it work for you when you try to import a file that doesn't exist? (IE does it complain that a file doesn't exist, or just exits with -1?)

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