For future reference my test setup to try and break context properties.
main.cpp:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QHash>
#include <QRandomGenerator>
#include <QObject>
#include <QDebug>
class ContextSetter : public QObject
{
Q_OBJECT
// test multiple context properties in one object
Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
QString m_name;
public:
ContextSetter(QObject* parent=nullptr)
: QObject(parent)
{}
QString name() const
{
return m_name;
}
public slots:
void setName(QString name)
{
if (m_name == name)
return;
m_name = name;
emit nameChanged(m_name);
}
signals:
void nameChanged(QString name);
};
class ContextHolder : public QObject
{
Q_OBJECT
public:
ContextHolder(QObject* parent=nullptr)
: QObject(parent)
, m_rootcontext(nullptr)
{
m_seededgen = QRandomGenerator::securelySeeded();
}
void setrootcontext(QQmlContext* context){
m_rootcontext = context;
}
QQmlContext* rootcontext(){
return m_rootcontext;
}
public slots:
QString createContextPropertyObject(QString name = QString()){
if(m_rootcontext){
char set = std::round(m_seededgen.generateDouble()) ? 'a' : 'A';
char head = set + std::floor(m_seededgen.generateDouble() * 26); // a to Z
int body = std::round(m_seededgen.generateDouble() * 100000);
QString propname;
if(name.length())
propname = name;
else
propname = QString("%1%2").arg(head).arg(body);
auto obj = new ContextSetter(this);
obj->setName(propname);
m_propobjects[propname] = obj;
m_rootcontext->setContextProperty(propname, obj);
qDebug() << "Created:" << propname;
return propname;
}
return QString();
}
void deleteContextPropertyObject(QString propname){
if(m_propobjects.contains(propname)){
auto obj = m_propobjects[propname];
m_propobjects.remove(propname);
obj->deleteLater();
m_rootcontext->setContextProperty(propname, nullptr);
qDebug() << "Deleted:" << propname;
}
}
private:
QQmlContext* m_rootcontext;
QHash<QString, QObject*> m_propobjects;
QRandomGenerator m_seededgen;
};
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
auto rootcontext = engine.rootContext();
ContextHolder cholder;
cholder.setrootcontext(rootcontext);
rootcontext->setContextProperty("contextholder", &cholder);
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl) {
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
return app.exec();
}
#include "main.moc"
main.qml:
import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Window 2.12
Window {
id: mainwin
width: 640
height: 480
visible: true
title: qsTr("setContextProperty object deletion testing")
property var proplist: []
Timer {
id: createtimer
interval: 1000
repeat: true
running: true
onTriggered: {
var propname = contextholder.createContextPropertyObject()
proplist.push(propname)
}
}
Timer {
id: deletetimer
interval: 1000
repeat: true
running: true
onTriggered: {
var propname = proplist.pop()
contextholder.deleteContextPropertyObject(propname)
}
}
Timer {
id: cycledialog
interval: 500
repeat: true
running: true
property string propname: "KillMe"
Component.onCompleted: {
contextholder.createContextPropertyObject(propname)
contextholder.deleteContextPropertyObject(propname)
}
onTriggered: {
contextholder.createContextPropertyObject("Atestobject")
contextholder.createContextPropertyObject("atestobject")
contextholder.createContextPropertyObject("Ztestobject")
contextholder.createContextPropertyObject("ztestobject")
contextholder.createContextPropertyObject("Qtestobject")
contextholder.createContextPropertyObject("qtestobject")
testdialogloader.active = true
}
}
Loader {
id: testdialogloader
active: false
sourceComponent: testdialog
}
Component {
id:testdialog
Rectangle {
width: 200
height: 200
color: "red"
Column {
Text {
text: Atestobject.name
}
Text {
text: atestobject.name
}
Text {
text: Ztestobject.name
}
Text {
text: atestobject.name
}
Text {
text: Qtestobject.name
}
Text {
text: qtestobject.name
}
Text {
text: "propname: " + KillMe
}
}
Timer {
id: disabletimer
interval: 250
repeat: false
running: true
onTriggered: {
testdialogloader.active = false
contextholder.deleteContextPropertyObject("Atestobject")
contextholder.deleteContextPropertyObject("atestobject")
contextholder.deleteContextPropertyObject("Ztestobject")
contextholder.deleteContextPropertyObject("ztestobject")
contextholder.deleteContextPropertyObject("Qtestobject")
contextholder.deleteContextPropertyObject("qtestobject")
}
}
}
}
}
Notice if you comment out:
m_rootcontext->setContextProperty(propname, nullptr);
Then it will crash on accessing the KillMe context property. So setting a previously used context property to nullptr is a way to protect yourself from seg faults.
