Replace logging backend for console.debug() console.warn() - qt

Question

Qt Quick uses qDebug to perform logging, where the standard Javascript logging methods are maped to a Qt log type
console.log() -> qDebug()
console.debug() -> qDebug()
console.info() -> qDebug()
console.warn() -> qWarning()
console.error() -> qCritical()
At this point you loose the distinction between debug() and info().
Is there any way to register a custom logger for the Javascript methods directly in the QML engine without going over qDebug and qInstallMessageHandler?

Answer 1

Although the globalObject is read-only in the QQmlEngine, values stored therein are not. So you can modify the console property of the globalObject. You can do that both in C++ and in QML. Here is a trivial running example in QML:
import QtQuick 2.3
import QtQuick.Controls 1.2
ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Console example")
Column {
anchors.centerIn: parent
Button {
text: "debug"
onClicked: {
console.log = console.debug
}
}
Button {
text: "exception"
onClicked: {
console.log = console.exception
}
}
Button {
text: "print something"
onClicked: {
console.log( "logging something" );
}
}
}
}
The first two buttons change, what the third button does by modifying the console.log method. C++ would look something like this (I cannot copy all of my code here, sorry, but it should get you going and it works nicely):
// in a header file
class HelperObject: public QObject {
Q_OBJECT
// ...
public slots:
myLog( QString aMessage );
};
// in an implementation file
QQmlEngine qmlEngine;
HelperObject helperObject;
QJSValue helperValue = qmlEngine.newQObject( &helperObject );
QJSValue consoleObject( qmlEngine.globalObject().property( "console" ) );
if (!consoleObject.isUndefined()) {
QJSValue myLogValue = helperValue.property( "myLog" );
consoleObject.setProperty( "log", myLogValue );
}