How to add and access informations from dynamically created objects QT

[frnklu20]

I'm developing a program that basically adds labels (with drag and drop function and with clicked signal) on the screen and when I click in 2 dynamically added objects, I draw a line between

But now i'm wondering how to add and access informations from those dynamically objects, in clear english, how the program will know that i'm clicking the object with the informations that i want?

My ideia was:

When i click on the screen -> add a label portraying the object that i want (let's say it is a car)
At the same moment->create a new object from the class Car
##The class Car has a variable named "position", that will be the position of the label that represents that object##
in the other line-> Car->position=event->pos() that is the position of the cursor when i create the label

And ok, now how i'll do the link?I'm pretty lost right now

That is my code

customlabel.cpp->the class in charge to handle the clicks on the labels emitting a singal with the position of the clicked labels

CustomLabel::CustomLabel(QWidget *parent):QLabel(parent) {
    this->setMouseTracking(true);
    this->setCursor(Qt::OpenHandCursor);
}


void CustomLabel::mousePressEvent(QMouseEvent *event) {
    QPoint mouse_pos=event->pos();
    diagrama=new Diagrama();

    if(event->button()==Qt::RightButton &&diagrama->modo=="linha") {

        if(mouse_pos.x()<=this->size().width() && mouse_pos.y()<=this->size().height()) {

            if(mouse_pos.x()>0 && mouse_pos.y()>0) {
                emit sendMousePosition(this->pos());
            }
        }
    } else {
        event->ignore();
    }
}

diagrama.cpp->thats the class that draw lines with between the labels, add labels dynamicaly, gives the ability of drag and drop to the labels etc

void Diagrama::showMousePosition(const QPoint &pos)##slot that receives the position of the click on a label
{
    QPoint p=pos;
    pontos.append(p);
    update();
}
...
drag and drop functions
...
void Diagrama::mousePressEvent(QMouseEvent *event)
{....
if(modo=="barramento")
    {
        if(event->button()==Qt::RightButton)
        {
            CustomLabel *child = new CustomLabel(this);
            child->setPixmap(QPixmap(url_barram));
            child->move(event->x(),event->y());
            connect(child, &CustomLabel::sendMousePosition, this, &Diagrama::showMousePosition);##create the labels when i click on the screen
            child->show();
        }
    }

barramento.h->thats the class wich stores all the informations needed of the portrayed object

class Barramento
{

public:
    explicit Barramento(QWidget* parent =0 );
    Barramento();
    QString nome="padrão";
    int num;
    float tensao;
    float ang;
    QPoint pos;
};

Please, help. sz
Just give a me a hand

[mrjj]

Hi
just to be sure i understand the issue
when you click a CustomLabel on screen, you want to somehow to have it related to a
Barramento instance ?
So when you click a CustomLabel, you need some way to know which
Barramento it represents?
or ?

[frnklu20]

YES,exactaly !!!!!

to start i would add manually some informations in the created object, and when i click it, it would appear a messagebox with the informations of that object (just an ideia i don't know)

but how can relate the label and the instance?thats the first step!

[mrjj]

@frnklu20
Well there various ways to do that.
You can add a
Barramento *MyBarramento;
to CustomLabel and assign its Barramento when you create label.
Then it points directly to its data.
(it can also be a non pointer if u wish)

Alternatively, you can have the Barramento in a map and use an id to allow label to look it up.
std::map<QString, Barramento *> BarramentoMap;
BarramentoMap["Car"] = new Barramento;
and you give "Car" to label as its data ID.
This works well if it is not really the CustomLabel that needs the data but something outside of it. So when you click on a label, you can look up data.

[frnklu20]

I think that using a map is the better option, but i've never heard Qmap for example.
I'm kinf of new in Qt... how Qmap works?

[frnklu20]

@mrjj
I saw some videos about Qmap and map in c++ and it is like a dictionary in python i guess
The problem is that the labels that i add on the screen don't have a specific name , all of them are named as 'child' as you can see in the code.
Is that a way that i can use it?

[mrjj]

@frnklu20
Hi
Yes map is like a dictionary. You insert a key and its data.
you can then use key to get data back.

You dont need to use labels name. you can use a dynamic property that just has to match
the id you use for its Barramento;
say
std::map<QString (this is key type) , Barramento * ( this is data) > BarramentoMap;
BarramentoMap["Car"] = new Barramento;
than key Car stores some Barramento

When you create the CustomLabel
you can set property
CustomLabel *lab = new CustomLabel();
lab->setProperty("datakey", "Car");
(or simply add a QString datakey to class CustomLabel to hold it )

in either case, when you click on a Label, you can use its property("datakey") or its
variable to look the actual data up in the list.

You could also add new clicked signal to the CustomLabel that includes the data ID so its send to the slot.
and you can directly look data up.

[frnklu20]

Okay, please be patient with me, i really need your help!

In my mousePressEvent of diagrama.cpp i have:

void Diagrama::mousePressEvent(QMouseEvent *event)
{...

            CustomLabel *child = new CustomLabel(this);
            child->setPixmap(QPixmap(url_barram));
            child->move(event->x(),event->y());
            connect(child,&CustomLabel::opendialog, this, &Diagrama::justopendialog);
            child->show();
            Barramento *barramento=new Barramento(this);##create a new barramento
            BarramentoMap["barramento"]=barramento;      
            child->setProperty("datakey","barramento");##link the new label with the new barramento

And my customlabel class is:

void CustomLabel::mousePressEvent(QMouseEvent *event){


    QPoint mouse_pos=event->pos();
    diagrama=new Diagrama();

    if(event->button()==Qt::RightButton &&diagrama->modo=="linha"){

    if(mouse_pos.x()<=this->size().width() && mouse_pos.y()<=this->size().height()){

    if(mouse_pos.x()>0 && mouse_pos.y()>0){
          emit sendMousePosition(this->pos(),this->property("datakey"));
       }

Now in my signal I emit the position of the label that i clicked and his property("datakey"), can I do it?

Is that it?Or there is something wrong or missing?

[SGaist]

@frnklu20 said in How to add and access informations from dynamically created objects QT:

QPoint mouse_pos=event->pos();
diagrama=new Diagrama();

if(event->button()==Qt::RightButton &&diagrama->modo=="linha"){

You just created diagrama , does this test really make sense ?

[frnklu20]

yes, it does.
In my diagrama class i have some modes and this clicked signal is only emitted when the mode "linha" from diagram is on!

Relax, this is not the problem!Do you know if what i did works?

[mrjj]

@frnklu20
Hi
Seems fine if you also changed the signal sendMousePosition to also have a QVariant in it parameter list.
You could make it a QString and do
emit sendMousePosition(this->pos(),this->property("datakey").toString());

[frnklu20]

Yes, I did it!
This is the slot that handles the signal:

void Diagrama::showMousePosition(const QPoint &pos, const QVariant property)
{
    QPoint p=pos;
    pontos.append(p);##this is to draw a line between the object
    update();
    QMessageBox::about(this,"info",property.toString());##to start i want to just open a message box and show the information, it is temporary before i do something nice
}

There is only one problem, the class barramento is like this:

barramento.h

class Barramento
{

public:
    explicit Barramento(QWidget* parent =0 );
    Barramento();
    QString nome="padrão";
    int num;
    float tensao;
    float ang;
    QPoint pos;
};

barramento.cpp

#include "barramento.h"

Barramento::Barramento()
{

}

This class is like this because i don't need any function, I just need to store informations on those variables.

And when i run the program it gives me an error:
undefined reference to 'Barramento::Barramento(QWidget*)' it happens in the line when i create a new Barramento.

[mrjj]

Hi
you need (also)
Barramento::Barramento( QWidget* parent )
{

}

however, you dont really need it as its not a widget
so you can just delete it completely. (also in .h)

class Barramento
{
public:
    QString nome="padrão";
    int num;
    float tensao;
    float ang;
    QPoint pos;
};

[frnklu20]

It worked!!

THANK YOU <3

You´re an angel man, for real.

I only changed a detail:
Each barramento represents a diferent object with different informations and etc
So i did this:

void Diagrama::mousePressEvent(QMouseEvent *event)
{...
if(modo=="barramento")
    {
        if(event->button()==Qt::RightButton)
        {
            Barramento *barra=new Barramento(this);
            int i=0;
            i+=1;
            BarramentoMap["barramento"+QString::number(i)]=barramento;
            child->setProperty("datakey","barramento"+QString::number(i));
}
...

every time i click on the screen with the mode barramento on, I add 1 to this "i" variable and now when i click on the label it send me a signal in the form "barramento"+i.toString()

dealing with the signal:

void Diagrama::showMousePosition(const QPoint &pos, const QVariant property)
{
    QPoint p=pos;
    pontos.append(p);
    update();
    QMessageBox::about(this,"info",BarramentoMap[property.toString()]->nome);
}

And i can access each object separately!
I don't know if it is the best way, but i'm quite happy now that it is working!

Thank you again SZ

[mrjj]

@frnklu20
Hi
Super. :)
Looks fine.
One note:
You say
if(event->button()==Qt::RightButton)
{
Barramento *barra=new Barramento(this);
int i=0;
i+=1;
BarramentoMap["barramento"+QString::number(i)]=barramento;
child->setProperty("datakey","barramento"+QString::number(i));

so if you would call this code more than once, it would still get "barramento1" as key
and override any barramento1 already put there. Might not be an issue but i did wonder.

Just a note2, about clean up.
I can see you assign
Barramento *barra=new Barramento(this); >> the this
as parent.
Do you have
class Barramento : public QObject <<<
{

so it becomes part of the parent/owner system ?

Else, we are currently leaking the Barramento in the list as nothing will delete them on close down.
Not a big issues as the OS will clean it up when you close but im just old school and like it to be certain.

[frnklu20]

"so if you would call this code more than once, it would still get "barramento1" as key
and override any barramento1 already put there. Might not be an issue but i did wonder."

That's the point! the user change the informations of the barramento
that he wants

"so it becomes part of the parent/owner system ?"
yes, it becomes part of Diagrama class

My point here is when i click on the screen add a label that represents a barramento object created at the same time.We're ok with that now

The next step is to add and change informations about it.You already saw the variables in class barramento,so here is what i thought:

When i create the label on the screen, i execute a Dialog from the class BarramDialog

And to get those values, i did:

if(modo=="barramento")
    {
        if(event->button()==Qt::RightButton)
        {
           int i=0;
            i+=1;
            CustomLabel *child = new CustomLabel(this);
            BarramDialog *barram=new BarramDialog;
            barram->setModal(true);

            child->setPixmap(QPixmap(url_barram));
            child->move(event->x(),event->y());
            connect(child, &CustomLabel::sendMousePosition, this, &Diagrama::showMousePosition);
            connect(child,&CustomLabel::opendialog, this, &Diagrama::justopendialog);
            child->show();
            barram->exec();##executing the dialog right after i create the label

            Barramento *barramento=new Barramento(this);
            barramento->setnum(barram->num);
            barramento->setang(barram->ang);
            barramento->settensao(barram->tensao);##getting those input values on the BarramDialog
            barramento->setnome(barram->nome);
            BarramentoMap["barramento"+QString::number(i)]=barramento;
            child->setProperty("datakey","barramento"+QString::number(i));
        }
    }

barramento.h

class Barramento
{

public:
    explicit Barramento(QWidget* parent =0 );
    Barramento();
    QString nome="padrão";
    int num;
    float tensao;
    float ang;

    void setnome(QString &);
    void setnum(int &);
    void settensao(float &);#these functions are responsible to change the variable values that i want 
    void setang(float &);

};

"Else, we are currently leaking the Barramento in the list as nothing will delete them on close down."
So how can i delete them?
" im just old school and like it to be certain." i get it hahaha

[mrjj]

@frnklu20 said in How to add and access informations from dynamically created objects QT:

ok. super its works as you want, no reason for alarm about the id.

So how can i delete them?

Well if you don't use the parent parameter in
explicit Barramento(QWidget* parent =0 );

then you can simply loop the and and call delete on each.
disclaimer*: fast typed. might have errors.

for (auto const& x : BarramentoMap)
{
delete x.second;
}

a good place to do it , would be the destructor of the main window. or where the BarramentoMap lives.

[frnklu20]

Ok! i'll do it

Just one more question, how can i do to support this link between the label and the class barramento with drag and drop functions?

diagrama.cpp

void Diagrama::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

void Diagrama::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

void Diagrama::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
        QDataStream dataStream(&itemData, QIODevice::ReadOnly);

        QPixmap pixmap;
        QPoint offset;
        dataStream >> pixmap >> offset;

        CustomLabel *newIcon = new CustomLabel(this);
        newIcon->setPixmap(pixmap);
        newIcon->move(event->pos() - offset);
        newIcon->show();
        newIcon->setAttribute(Qt::WA_DeleteOnClose);
        connect(newIcon, &CustomLabel::sendMousePosition, this, &Diagrama::showMousePosition);
        connect(newIcon,&CustomLabel::opendialog, this, &Diagrama::justopendialog);
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

these are the functions responsible for that, and the problem is on
void Diagrama::dropEvent(QDropEvent *event)

in this function i create another label with the same pixmap that i'm moving and i delete(just guessing) the old one, so the new one has no barramento object linked to it

what i thought was to get the property("datakey") of the old label (which is emitted by CustomLabel class) and do something like this:

new_label->setProperty("datakey",property("datakey"))
with this new line, the new_label overrides the informations of the old one, wich is not a problem beacuse it doesn't exist anymore.

But how can i do it? since that i don't have the emitted signal of custom label in drag and drop?

[mrjj]

Hi
Since you already pack some data
(the dataStream >> pixmap >> offset; )
could you not just include a QString with its datakey ID
with the pixmap and offset and set it on the newly created label?

[frnklu20]

ok, but how?

let's say I do this:
QString data;

dataStream>>pixmap>>offset>>data;

how the program will know that data=this->property("datakey")?