[SOLVED] parameter in constructor of a custom qquickitem

sierdzio

Add a default value to that new parameter, so that QML engine can discard it when generating meta objects. When constructing the object by hand in JavaScript or C++, that parameter will still be available.

matteli

Thanks for attention.
But i want a parameter in the qml instance of my class.
I put a piece of my code illustring the problem.

main.ccp
@
#include <QGuiApplication>
#include "map.h"
#include "model.h"
#include <thread>
#include "message.h"
#include <QQuickView>

int main(int argc, char *argv[])
{
unsigned int width = 1024;
unsigned int height = 608;

QGuiApplication app(argc, argv);

Model model;
model.moveToThread(&model);
model.start();

qmlRegisterType<Map>("Histemul", 0,1, "Map");

QQuickView view;

view.setSource(QUrl::fromLocalFile&#40;"ui.qml"&#41;);
view.setClearBeforeRendering(false);

view.show();


return (app.exec());

}
@

ui.qml
@
import QtQuick 2.0
import Histemul 0.1

Item {
Map {
fill: "land"
...
}
...
}
@

With that, there is no problem. But now i want to pass to the constructor of the class Map the object model and i want to access model in the object constructed in qml.

sierdzio

There is no mechanism in QML that I know of that would allow you to do that. You need to change your approach: for example, add a new Q_INVOKABLE method like "initialise()" to your c++ class, and then in QML call:
@
Map {
Component.onCompleted: {
initialise();
}
}
@

This will fill your object. Another approach would be to use a singleton and access it in the default constructor.

sierdzio

Or just use the Q_PROPERTY setter to adapt every time "fill" changes.

matteli

But in all your approch, the class Map can't access "model" object declared in the main function. When i changed the fill, i used setFill Q_PROPERTY but in this function, i need to acess to the "model" object.

Before used the qquickitem, i have tried to use QQuickWindow::beforeRendering() signal to connect with the painting function but because of problem, i prefered used qquickitem.
When i have tried this, my constructor was :
@
Map::Map(int width, int height, int initialBlock, const QUrl & source, Model & model): QQuickView(source) , mWidth(width), mHeight(height), mTopLeftBlock(initialBlock), mModel(model)
@
but the qquickitem needs a defaut constructor

I tried the singleton but it doesn't seems to work.

The only approch i see for the moment is to use a double signal/solt connected.
One signal when i'm in the setFill function connected to a slot in my function in Model class and at the end of the function a signal connected to a slot to a function in the Map Class.

matteli

The double signal/slot will not work because i can't access the object Map instanced in the qml code.

sierdzio

[quote author="matteli" date="1357994339"]The double signal/slot will not work because i can't access the object Map instanced in the qml code.[/quote]

You need to set object name:
@
// QML
Map {
objectName: "myName"
}

// C++
parent->findChild("myName");
@

Why didn't the singleton work? You should make Model class into a singleton and then it would be available in every place that has it's header included.

matteli

Ah ok, i tried a singleton with the class Map.

What do you think to use setContextProperty for exposing the model object to qml code ?

sierdzio

You can do that if you wish, too. I don't know your app, so I can't say if it's required. Sometimes it's enough just to have it in c++, sometimes it's needed in QML, too.

matteli

ok i resolve my problem. I give a solution for others which have this problem.

Objective : Give access to a object (named : model) for a qquickitem (named : map).

Problem : for using a class as a custom quickitem, you must used qmlRegisterType which only support defaut constructor for the class. There is no possible to give a reference to model during the construction of map in qml code.

My solution according to sierdzio suggestion :

main.cpp
@
#include <QGuiApplication>
#include "map.h"
#include "model.h"
#include <thread>
#include <QQuickView>

int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);

Model model;
model.moveToThread(&model);
model.start();

qmlRegisterType<Map>("MyLib", 0,1, "Map");

QQuickView view;

view.setSource(QUrl::fromLocalFile&#40;"ui.qml"&#41;&#41;;
view.setClearBeforeRendering(false&#41;;

/* After the construction of map in QML code, i continue the init here*/
Map* map = rootQml->findChild<Map *>("map");
map->init(model);

view.show();

return (app.exec&#40;&#41;&#41;;

}

@

map.h
@
#ifndef MAP_H
#define MAP_H
#include "model.h"
#include <QQuickItem>

class Map : public QQuickItem
{
Q_OBJECT

public:
Map();
~Map();

void init(Model &model);

private:
//members
Model *mModel;

//methods
QSGNode *updatePaintNode(QSGNode * oldNode, UpdatePaintNodeData * updatePaintNodeData);

};
#endif // MAP_H
@

map.cpp
@
Map::Map()
{
setFlag(QQuickItem::ItemHasContents, true);
}

Map::~Map()
{
delete mModel;
}

void Map::init(Model &model)
{
mModel = &model;
return;
}
@

ui.qml
@
import QtQuick 2.0
import MyLib 0.1
Item {
Map {
id: map
objectName: "map"
}
}
@

Thank you sierdzio

sierdzio

I'm happy you have found a solution. Please add [Solved] to the beginning of your topic's title. I've already tagged it as solved for you.