How can i pass data between Qwidgets forms?

Eduardo12l

@Flotisable Ok, I'm quite new at C++ . I have a problem yet in Dialog2.cpp
This is my QList<int> L .This time im not using an array (LunINI), im using L.

Dialog2.h

public:
    explicit Dialog2(QWidget *parent = 0);
    Dialog2(QWidget *parent = 0, const QString curso = "", const int numero = 0);
    int n = 0;
    int LunINI[24];
    QList <int> L;

Dialog3.h

class Dialog3 : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog3(QWidget *parent = 0);
    Dialog3(QWidget *parent = 0, QList<int> *L = 0);
    ~Dialog3();
private:
    int LunINI[24];
    QList <int> L;
    Ui::Dialog3 *ui;
};

Dialog2.cpp

void Dialog2::on_pushButton_clicked(){
    Dialog3 *v = new Dialog3(this, L); //ERROR C2664 "cannot convert parameter 2 from 'QList<int>'  to  'QList<int>* '"
    close();
    v->show();
}

Dialog3.cpp


Dialog3::Dialog3(QWidget *parent, QList<int> *L) :
    QDialog(parent),
    ui(new Ui::Dialog3), L(*L)
{
    ui->setupUi(this);
}

jsulm

@Eduardo12l You should use QVector if you're going to use it like an array as it is much more efficient for this than QList.

Dialog3 *v = new Dialog3(this, L); //ERROR C2664 "cannot convert parameter 2 from 'QList<int>'  to  'QList<int>* '"

that's because Dialog3() constructor takes a pointer:

Dialog3 *v = new Dialog3(this, &L);

Flotisable

@Eduardo12l
to add @jsulm , you can use const reference instead of pointer in your Dialog3's constructor

this way, you don't need to use & and *operator, I think it will make it more readable in your code

Eduardo12l

@jsulm Thx this time Qt doesn't show an error message

Eduardo12l

@Flotisable I dont understand, Do you mean that should add "const" instead of &?

I mean

Dialog3 *v = new Dialog3 (this, **const** L )

Flotisable

@Eduardo12l
no, I mean

Dialog3::Dialog3( QWidget *parent, const QList<int> &L ) :
    QDialog( parent ), ui( new Ui::Dialog3 ), L( L )

and

Dialog3 *v = new Dialog3( this, L );

Eduardo12l

@Flotisable It doesnt work but anyway thx ^^

jsulm

@Eduardo12l What does not work? What is the error?

Eduardo12l

@jsulm What Flotisable says doesnt work. The code is below:

Dialog2.h

public:
    explicit Dialog2(QWidget *parent = 0);
    Dialog2(QWidget *parent = 0, const QString curso = "", const int numero = 0);
    int n = 0;
    int LunINI[24];
    QList<int> L;
    ~Dialog2();

Dialog3.h:

public:

    explicit Dialog3(QWidget *parent = 0);
    Dialog3(QWidget *parent = 0, const QList<int> &L=0); // ERROR C2440: Cannot convert from 'INT' to 'const QList<int>&'
    ~Dialog3();

private:
    int LunINI[24];
    QList <int> L;
    Ui::Dialog3 *ui;

Dialog2.cpp

void Dialog2::on_pushButton_clicked(){
    Dialog3 *v = new Dialog3(this, L); 
    close();
    v->show();
}

Dialog3.cpp

Dialog3::Dialog3(QWidget *parent, const QList<int> &L) :
    QDialog(parent),
    ui(new Ui::Dialog3), L(L)
{
    ui->setupUi(this);
}

SGaist

Hi,

You can't assign 0 to QList container. That's the error. You have to assign it an empty QList value if you want a default value for it.

On a side note, the common pattern is to have the parent parameter as the last in the constructor.

Eduardo12l

@SGaist Thx but How can i assign an empty QList value?

Flotisable

@Eduardo12l
since you have overloaded constructor, you don't need to give L a default value.
if you want, you can use

  Dialog3( QWidget *parent = 0, const QList<int> &L = QList<int>() )

QList<int>() will construct a QList<int> instance with empty value.

for what @SGaist says, you can modify the constructor this way

Dialog3( const QList<int> &L = QList<int>(), QWidget *parent = 0 )

as I have said, you don't need to set a default value for L, so

Dialog3( const QList<int> &L, QWidget *parent = 0 )

is enough