I hope someone can help me with this. I have an external QML Module which accepts a QStringList as parameter. However, what I have is a simple String. My question is: Is there a way in QML to convert a list of Strings into a QStringList without any external c++ functions?
Thanks
I tried to pass a simple string but it is not accepted.
You can use a JavaScript array of strings or list<string> depending on your Qt version. Have a look here.
main.qml
import QtQuick
Rectangle {
id: root
width: 640
height: 480
property var jsArray: ["apple", "banana", "mango"]
property list<string> stringList: ["Oslo", "Berlin", "New York"]
Component.onCompleted: {
var arr = ["more", "strings", "here"]
applicationData.setSomething(arr)
applicationData.setSomething(root.stringList)
applicationData.setSomething(root.jsArray)
}
}
main.cpp
#include <QGuiApplication>
#include <QQmlContext>
#include <QQuickView>
class ApplicationData : public QObject
{
Q_OBJECT
public:
Q_INVOKABLE void setSomething(const QStringList &list) const
{
for (const auto &s : list)
qDebug() << s;
}
};
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQuickView view;
ApplicationData data;
view.rootContext()->setContextProperty("applicationData", &data);
view.setSource(QUrl(u"qrc:/75085103/main.qml"_qs));
view.show();
return app.exec();
}
#include "main.moc"
Related
If Qml can do
MyComponent.connect(someJsFunction);
how can I do this on c++ ???
I need connect JSValue if it isCallable without workarounds. I want to know how it makes qml engine...
QObject::connect(QObject, signal, QJSValue, evaluateFunctionSlot);
This will work. I got the solution from this SO post. That said, I don't know if it aligns with the Qt way of doing it. Their example of invoking a QML method uses QMetaObject::invokeMethod().
main.cpp
#include <QGuiApplication>
#include <QQuickItem>
#include <QQuickView>
class MyClass : public QObject
{
Q_OBJECT
signals:
void cppSignal(const QString &msg);
};
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQuickView view(QUrl(u"qrc:/75069400/main.qml"_qs));
view.show();
QObject *item = view.rootObject();
MyClass myClass;
QObject::connect(&myClass, SIGNAL(cppSignal(QString)),
item, SLOT(callFromCpp(QString)));
emit myClass.cppSignal("this is a test");
return app.exec();
}
#include "main.moc"
main.qml
import QtQuick
Rectangle {
width: 320
height: 240
function callFromCpp(value : string) {
console.log("QML" , value)
}
}
As result the best workaround:
qml
function connect(name, fn){
myObject[name].connect(fn[name]);
}
c++
QMetaObject::invokeMethod(MyObject, "connect", Q_ARG(QVariant, "anySlotName"), Q_ARG(QVariant, QVariant::fromValue(data)));
I'm trying to update a MapCircle in QML from a signal in C++ and I'm veen having several issues with it all day.
In my class I have a Q_PROPERTY which is read only and holds the GPS positions of 4 UAVs in a QVariantList
class GCS: public QObject
{
Q_PROPERTY(QVariantList getUavPosition READ getUavPosition NOTIFY uavPositionSet)
public:
QVariantList getUavPosition() ;
signals:
void uavPositionSet();
public slots:
void setUavPosition();
void triggerPosition();
private:
QVariantList connected_uavs;
QVector<QGeoCoordinate> uav_positions;
};
I then define the functions as:
void GCS::setUavPosition()
{
double i = 0.0;
QGeoCoordinate uav_id;
uav_id.setLatitude(0.5);
uav_id.setLongitude(0.5 + i);
uav_id.setAltitude(5);
uav_positions.insert(0, uav_id);
connected_uavs.append( QVariant::fromValue(QGeoCoordinate(uav_positions[0].latitude(), uav_positions[0].longitude())));
i+=0.15;
emit uavPositionSet();
}
QVariantList GCS::getUavPosition()
{
return connected_uavs;
}
void GCS::triggerPosition()
{
setUavPosition();
ROS_INFO("Pos trig");
}
In my main function, I connect triggerPosition to a Timer so as to update the position periodically
int main(int argc, char *argv[])
{
ros::init(argc, argv, "planner");
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QQmlContext* context = engine.rootContext();
GCS gcs;
context->setContextProperty("planner", &gcs);
engine.load(QUrl(QStringLiteral("qrc:/planner.qml")));
QTimer *timer = new QTimer();
timer->setInterval(1000);
QObject::connect(&gcs, SIGNAL(uavPositionSet()), &gcs, SLOT(setUavPosition()));
QObject::connect(timer, SIGNAL(timeout()), &gcs, SLOT(triggerPosition()));
timer->start();
return app.exec();
}
However, when I run my program, there's a slight delay, my mouseArea becomes unusable and the program crashes. When I try to print the longitude to see if it updates, The initial value is printed out multiple times to the terminal but then the program crashes and there's is no MapCircle present on the map
The relevant part of My Qml file looks like this:
Map{
id: map
anchors.fill:parent
plugin: mapPlugin
center: QtPositioning.coordinate(0.5, 0.5)
zoomLevel:50
MapCircle{
id:uavPos
radius:2
color:'black'
border.width:3
}
Connections{
id:uavConnection
target: planner
onUavPositionSet:{
var data = planner.getUavPosition
uavPos.center = QtPositioning.coordinate(data[0].latitude, data[0].longitude)
console.log(data[0].longitude)
}
}
}
Can someone please kindly point me in the right direction here?
If you are going to handle information from several elements then it is better to use a model (together with a Repeater to create several elements), so it is only necessary to modify the role of an item:
gcs.h
#ifndef GCS_H
#define GCS_H
#include <QObject>
class QStandardItemModel;
class QAbstractItemModel;
class GCS: public QObject
{
Q_OBJECT
Q_PROPERTY(QObject* uavModel READ uavModel CONSTANT)
public:
enum UAVRoles {
PositionRole = Qt::UserRole + 1000
};
GCS(QObject *parent=nullptr);
QObject *uavModel() const;
public Q_SLOTS:
void triggerPosition();
private:
QStandardItemModel* m_uavModel;
};
#endif // GCS_H
gcs.cpp
#include "gcs.h"
#include <QGeoCoordinate>
#include <QStandardItemModel>
#include <random>
GCS::GCS(QObject *parent):
QObject(parent), m_uavModel(new QStandardItemModel(this))
{
m_uavModel->setItemRoleNames({{PositionRole, "position"}});
for(int i =0; i < 4; i++){
QStandardItem *item = new QStandardItem;
item->setData(QVariant::fromValue(QGeoCoordinate()), PositionRole);
m_uavModel->appendRow(item);
}
}
QObject *GCS::uavModel() const{
return m_uavModel;
}
void GCS::triggerPosition(){
std::mt19937 rng;
rng.seed(std::random_device()());
std::normal_distribution<> dist(-0.0001, +0.0001);
if(QStandardItem *item = m_uavModel->item(0)){
QGeoCoordinate uav_id;
uav_id.setLatitude(0.5 + dist(rng));
uav_id.setLongitude(0.5 + dist(rng));
uav_id.setAltitude(5);
item->setData(QVariant::fromValue(uav_id), PositionRole);
}
}
main.cpp
#include "gcs.h"
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QTimer>
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
GCS gcs;
QQmlApplicationEngine engine;
QQmlContext* context = engine.rootContext();
context->setContextProperty("planner", &gcs);
const QUrl url(QStringLiteral("qrc:/planner.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);
QTimer timer;
timer.setInterval(1000);
QObject::connect(&timer, &QTimer::timeout, &gcs, &GCS::triggerPosition);
timer.start();
return app.exec();
}
planner.qml
import QtQuick 2.14
import QtQuick.Window 2.14
import QtLocation 5.14
import QtPositioning 5.14
Window {
visible: true
width: 640
height: 480
title: qsTr("Hello World")
Plugin {
id: mapPlugin
name: "osm"
}
Map{
id: map
anchors.fill:parent
plugin: mapPlugin
center: QtPositioning.coordinate(0.5, 0.5)
zoomLevel:50
MapItemView{
model: planner.uavModel
delegate: MapCircle{
id:uavPos
radius: 2
color:'black'
border.width:3
center: QtPositioning.coordinate(model.position.latitude, model.position.longitude)
}
}
}
}
This question already has answers here:
Qt5. Embed QWidget object in QML
(5 answers)
Closed 5 years ago.
For a while I thought that I was not able to use Qt c++ classes with qml applications, but I found this: http://doc.qt.io/qt-5/qtqml-cppintegration-definetypes.html.
Now I'm trying to create an instantiable object type. I first ran into "Qwidget: Cannot create a Qwidget without QApplication" reading online it the answer seem to be just to change QGuiApplication to QApplication, but then I get: "ASSERT: "
!d->isWidget"
This is the Qt class that I'm trying to use as a qml type: http://doc.qt.io/qt-5/qlcdnumber.html.
Here is my main.cpp:
#include <QApplication>
#include <QQmlApplicationEngine>
#include <QLCDNumber>
#include <QQuickStyle>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
qmlRegisterType<QLCDNumber>("LCDNumber",1,0,"LCDNumber");
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
Here is what I'm trying to create in main.qml:
...
import LCDNumber 1.0
Window {
...
LCDNumber{
digitCount: 3
intValue: 1
mode: LCDNumber.Dec
segmentStyle: LCDNumber.Flat
smallDecimalPoint: false
value: 0
}
}
Is it really possible to create a qt c++ class in qml? I'm missing something?
Yes, it's possible!
In your class use the Tags Q_PROPERTY and Q_INVOKABLE to provide into QML access to properties and methods class, like this:
class NameYourClass : public QDeclarativeItem {
Q_OBJECT
Q_PROPERTY(int intProperty1 READ getIntProperty1 WRITE setIntProperty1)
Q_PROPERTY(QString strProperty2 READ getStrProperty2 WRITE setStrProperty2)
private:
int intProperty1;
QString strProperty2;
public:
explicit NameYourClass(QDeclarativeItem *parent = 0);
~NameYourClass();
Q_INVOKABLE int getIntProperty1() const;
Q_INVOKABLE void setIntProperty1(int value);
Q_INVOKABLE QString getStrProperty2() const;
Q_INVOKABLE void setStrProperty2(const QString &value);
}
Your main.cpp:
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
qmlRegisterType<NameYourClass>("IdentifierName", 1, 0, "NameYourClass");
return app.exec();
}
Your QML file:
import IdentifierName 1.0
Rectangle {
id: nameRectangle
width: 999
height: 999
onSomethingChange: {
execFunction();
}
property NameYourClass nameDesired: nameObject
NameYourClass {
id: nameObject
intProperty1: 999
}
function execFunction() {
var varExample;
varExample = nameDesired.getIntProperty1();
nameDesired.setIntProperty1(varExample);
}
}
I do not think I've forgotten anything.
I hope it helps!
I have a Qt application and I'd like to show some log. I use a TextArea. However, if the log is large or the events come too fast the GUI can't draw Textarea fast enough.
I have analyzed this problem with Qt Creator (QML Profiler) and if the log is large it takes 300 ms to draw the GUI. I use this software on a Raspberry Pi2.
Any ideas how to solve this? Should I use other QML controls? Thanks.
QML code:
TextArea {
text: appHandler.rawCommunication
readOnly: true
}
C++ code:
Q_PROPERTY(QString rawCommunication READ rawCommunication WRITE setrawCommunication NOTIFY rawCommunicationChanged)
void setrawCommunication(QString val)
{
val.append("\n");
val.append(m_rawCommunication);
m_rawCommunication = val;
emit rawCommunicationChanged(m_rawCommunication);
}
Use a view, like ListView. They instantiate their delegates as needed, based on which data the view says it needs to show depending on the position the user is at in the list. This means that they perform much better for visualising large amounts of data than items like TextArea, which in your case is going to keep a massive, ever-growing string in memory.
Your delegate could then be a TextArea, so you'd have one editable block of text per log line. However, if you don't need styling, I'd recommend going with something a bit lighter, like TextEdit. Taking it one step further: if you don't need editable text, use plain old Text. Switching to these might not make much of a difference, but if you're still seeing slowness (and have lots of delegates visible at a time), it's worth a try.
I tried the ListView suggestion but it has several drawbacks:
No easy way to keep the view positioned at the bottom when new output is added
No selection across lines/delegates
So I ended up using a cached TextArea, updating once every second:
TextArea {
id: outputArea_text
wrapMode: TextArea.Wrap
readOnly: true
font.family: "Ubuntu Mono, times"
function appendText(text){
logCache += text + "\n";
update_timer.start();
}
property string logCache: ""
Timer {
id: update_timer
// Update every second
interval: 1000
running: false
repeat: false
onTriggered: {
outputArea_text.append(outputArea_text.logCache);
outputArea_text.logCache = "";
}
}
Component.onCompleted: {
my_signal.connect(outputArea_text.appendText)
}
}
try this approach:
create a c++ logger class
append all logs to this class
and print them using some action, example a button click
this will solve your performance issue
Example of code:
Logger.h
#ifndef LOGGER_H
#define LOGGER_H
#include <QQmlContext>
#include <QObject>
#include <QStringList>
#include <QQmlEngine>
#include <QString>
#include <QtCore>
#include <QDebug>
class Logger : public QObject
{
Q_OBJECT
public:
explicit Logger(QObject *parent = 0);
~Logger();
Q_INVOKABLE QStringList *getLogStream();
Q_INVOKABLE void printLogStream();
Q_INVOKABLE void appendLog(QString log);
Q_INVOKABLE void log(QString log="");
Q_INVOKABLE void log(QString fileName, QString log);
signals:
public slots:
private:
QStringList* stringStream_;
};
#endif // LOGGER_H
Logger.cpp
#include "logger.h"
Logger::Logger(QObject *parent) :
QObject(parent),
stringStream_(new QStringList)
{
}
~Logger(){
if(stringStream_ != NULL)
{
delete stringStream_;
stringStream_ = NULL;
}
}
QStringList* Logger::getLogStream(){
return stringStream_;
}
void Logger::printLogStream()
{
QStringListIterator itr(*stringStream_);
while (itr.hasNext())
qDebug()<< itr.next()<<"\n";
}
void Logger::appendLog(QString log){
stringStream_->push_back(log) ;
}
void Logger::log(QString fileName,QString log)
{
#ifdef ENABLElogs
fileName.push_front(" [");
if(!fileName.contains(".qml"))
{
fileName.append(".qml]:");
}
qDebug()<<fileName<<log;
#else
Q_UNUSED(log);
Q_UNUSED(fileName);
#endif
}
void Logger::log(QString log)
{
#ifdef ENABLElogs
qDebug()<<log;
#else
Q_UNUSED(log);
#endif
}
main.cpp
#include <QtGui/QGuiApplication>
#include "qtquick2applicationviewer.h"
#include "logger.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QtQuick2ApplicationViewer *viewer = new QtQuick2ApplicationViewer;
Logger* stream = new Logger;
viewer->rootContext()->setContextProperty("Stream",stream);
viewer->setMainQmlFile(QStringLiteral("qml/project/main.qml"));
viewer->showExpanded();
return app.exec();
}
main.qml
import QtQuick 2.0
import QtQuick.Controls 1.1
Rectangle {
width: 800
height: 480
Text {
text: qsTr("Hello World")
anchors.centerIn: parent
Component.onCompleted: Stream.appendLog("Text object is completed")
}
Column{
x:300
Button{
text:"append"
onClicked: {
Stream.appendLog("MouseArea object clicked")
}
Component.onCompleted: Stream.appendLog("Button object is completed")
}
Button{
text:"logger"
onClicked: {
Stream.printLogStream()
}
Component.onCompleted: Stream.appendLog("Button logger object is completed")
}
}
TextArea{
text:"blablabla"
Component.onCompleted: Stream.appendLog("TextArea object is completed")
}
Component.onCompleted: Stream.appendLog("the main object is completed")
}
project.pro
#add this line
# comment it, run qmake and recompile to disable logs
DEFINES += ENABLElogs
using this approch you can stop all logs with a single line change when you want to release your soft
However, I have included complete code, using "QAbstractListModel" for a Logging heavy data to QML
listmodel.h
#ifndef LISTMODEL_H
#define LISTMODEL_H
#include <QAbstractListModel>
class ListModel: public QAbstractListModel
{
Q_OBJECT
public:
ListModel();
// Q_PROPERTY(QStringList logs READ name WRITE nameChanged)
int rowCount(const QModelIndex & parent = QModelIndex()) const;
QVariant data(const QModelIndex & index, int role = Qt::DisplayRole) const;
Q_INVOKABLE QVariant activate(int i);
private:
QStringList m_list;
};
#endif // LISTMODEL_H
listmodel.cpp
#include "listmodel.h"
#include <QFile>
#include <QHash>
ListModel::ListModel()
{
QFile file("/home/ashif/LogFile");
if(!file.open(QIODevice::ReadOnly))
{
qDebug( "Log file open failed" );
}
bool isContinue = true;
do
{
if(file.atEnd())
{
isContinue = false;
}
m_list.append(file.readLine());
}
while( isContinue);
}
int ListModel::rowCount(const QModelIndex & parent ) const
{
return m_list.count();
}
QVariant ListModel::data(const QModelIndex & index, int role ) const
{
if(!index.isValid()) {
return QVariant("temp");
}
return m_list.value(index.row());
}
QVariant ListModel::activate(int i)
{
return m_list[i];
}
main.qml
import QtQuick 2.3
import QtQuick.Window 2.2
import QtQuick.Controls 1.4
Window {
visible: true
ListView
{
width: 200; height: 250
anchors.centerIn: parent
model:mylistModel
delegate: Text
{
text:mylistModel.activate(index)
}
}
}
main.cpp
#include <QGuiApplication>
#include <QQmlContext>
#include <QQmlApplicationEngine>
#include "logger.h"
#include "listmodel.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
Logger myLogger;
ListModel listModel;
engine.rootContext()->setContextProperty("mylistModel", &listModel);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
I dont know how to pass parameters from QML file to c++ file in Qt.
QML code:
import QtQuick 1.1
Rectangle{
id:loin
height: 272
width:480
property alias loguid:loginuid
signal sigHome()
Rectangle{
id:rect1
width:parent.width-80
height:24
TextInput {
id:loginuid
maximumLength: 16
width: maximumLength * 20
focus: false
validator: RegExpValidator { regExp: /\d+/ }
KeyNavigation.down: login1
}
}
Button{
id: login1
x: 195
y: 187
height:30;
focus:false
border.color:"black"
opacity: activeFocus ? 1.0 : 0.5
Text{
text:"LOGIN"
anchors.horizontalCenter:login1.horizontalCenter;
anchors.verticalCenter:login1.verticalCenter;
}
Keys.onReturnPressed: {
if(loginuid.text < 1000000000000000)
{
text1.opacity=0.1
error1.visible=true
errorText.text="\n enter valid 16 digit number\n"
errorOk.focus=true
loginuid.focus=false
}
else{
loginuid.focus=false
loin.sigHome()
}
}
}
}
c++ code:
#include <QApplication>
#include <QDeclarativeView>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
int uid;
QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
view.show();
return app.exec();
}
When I press the login button rect1.text content shud go to main.cpp file and uid in the main.cpp get dat value. Something like this uid=rect1.text.
How to do it?
I wouldn't try to listen for a QML signal from the C++ side. Calling a C++ method with arguments is much easier and achieves the same:
To do so you have to:
define a slot or invokable method accepting the required arguments
register the class carrying the method with the declarative engine
then you can set an instance of this class as a property of your root context and finally call this method from QML
This topic is also well covered in the official documentation.
Thanks, sebasgo, your response helped me. I used signals and slots to communicate.
I created a signal in main.qml.
signal info(string msg)
and in login page
else{
info(loginUid.text)
loginuid.focus=false
loin.sigHome()
}
and in main.cpp I connected it to d slot
main.cpp goes like this
#include <QtGui>
#include <QApplication>
#include <QDeclarativeView>
#include <QtDeclarative>
class DeclarativeView : public QDeclarativeView
{
Q_OBJECT
public:
DeclarativeView(const QUrl & source) : QDeclarativeView(source)
{
}
public slots:
void readText(QString quid)
{
qdebug<<quid;
}
};
#include "main.moc"
int main(int argc, char *argv[])
{
QString file = "main.qml";
QApplication app(argc, argv);
DeclarativeView view(QUrl::fromLocalFile(file));
QDeclarativeItem *item = qobject_cast<QDeclarativeItem *>(view.rootObject());
QObject::connect(item, SIGNAL(info(QString)), &view, SLOT(readText(QString)));
view.show();
return app.exec();
}
Create a GUI controller C++ class:
class UiController : public QObject
{
Q_OBJECT
public:
UiController();
virtual ~UiController();
public slots:
void cal_daysoff__onDoubleClicked(const QDate& date);
};
In QML file you define, say, a calendar control in which you connect a signal to a slot in the controller:
Calendar{
id: cal_daysoff
Layout.fillWidth: true
Layout.fillHeight: true
onDoubleClicked: UiController.cal_daysoff__onDoubleClicked(date)
}
In main file, when launching the QML interface, connect the interface to the controller:
#include "uicontroller.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
UiController control;
engine.rootContext()->setContextProperty("UiController", &control);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}