Object of QTableWidget

Armin

Hi
I write this code :
and i created a object of QTableWidget for public in mainwindows1.h

void MainWindow::on_pushButton_2_clicked()
{
    table.setCurrentCell(rowname , 1) = ui->textEdit->toPlainText();
    rowname = rowname++ ;
}

and i get this error :

C:\Users\armin\Documents\DataBase\mainwindow1.cpp:18: error: '((MainWindow*)this)->MainWindow::table' does not have class type
table.setCurrentCell(rowname , 1) = ui->textEdit->toPlainText();
^

Why i don't any access to my object of QTableWidget ?
Thanks

koahnig

@Armin

setCurrentCell returns void. Therefore, you cannot assign anything.

mrjj

Hi
Access to the items is via
http://doc.qt.io/qt-5/qtablewidget.html#item

table.setCurrentCell(rowname , 1) = ui->textEdit->toPlainText();

---->
QString text=ui->textEdit->toPlainText();
QTableWidgetItem *item=table.item(rowname , 1);
if (item)
item->setText(text);
else
qDebug() << "check rowname!!";

http://doc.qt.io/qt-5/qtablewidgetitem.html#setText

Armin

@mrjj said in Object of QTableWidget:

QTableWidgetItem *item=table.item(rowname , 1);

Thanks.
But i don't want create object in this function.
In fact i create function in header file and public class.

Armin

@koahnig
Thanks. so what i do?

koahnig

@Armin

QString text=ui->textEdit->toPlainText();      // you create a string object here
QTableWidgetItem *item=table.item(rowname , 1);       // you do not create an object here, you basically store the pointer
if (item)
    item->setText(text);
else
   qDebug() << "check rowname!!";

This would lok more compact, but laso kind of hard to read.

if (table.item(rowname , 1))
    table.item(rowname , 1)->setText( ui->textEdit->toPlainText() );
else
   qDebug() << "check rowname!!";

IMHO it is better to use the initial approach proposed by @mrjj . It is clearer for understanding what is happening. Performancewise both versions are probably at the day's end identical assuming that compiler will end up in the same optimization.

koahnig

@Armin

I just stumbled over your statement in the first post.

    rowname = rowname++ ;

I think in most cases it does not what you are expecting. I was not sure and wrote a small test application:

#include <QCoreApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    int rowname = 1;
    rowname = rowname++;
    qDebug() << rowname;
    rowname = rowname++;
    qDebug() << rowname;
    return a.exec();
}

The result is:

1
1

Tested on windows 10 with MiinGW Qt 5.4.2 in debug mode.

Armin

@koahnig said in Object of QTableWidget:

initial

Thanks
So Can't i access to member of object in class from function ? like this:

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    int row = 1;
    int clm = 7;
    QTableWidget *table (int row,int clm);
    int rowname = 1;



private slots:
    void on_pushButton_2_clicked();


private:
    Ui::MainWindow *ui;
};

#include "mainwindow1.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

 void MainWindow::on_pushButton_2_clicked()
{
    table.setCurrentCell(rowname , 1) = ui->textEdit->toPlainText();
    rowname = rowname++ ;
}

koahnig

@Armin

You can access a member in an object, but you are introducing a couple of problems in your code. I doubt that you get it compiled at all.

    int row = 1;                                                   // no possible this way
    int clm = 7;                                                   // see above
    QTableWidget *table (int row,int clm); // that is a declaration of a function called table
    int rowname = 1;                                       // same as first problem.

class MainWindow : public QMainWindow
{
    Q_OBJECT

    int row;
    int clm;
    QTableWidget *table;
    int rowname ;

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();



private slots:
    void on_pushButton_2_clicked();


private:
    Ui::MainWindow *ui;
};

#include "mainwindow1.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    row = 1;
    clm = 7;
   table = new QTableWidget (int row,int clm);
    rowname = 1;
}

MainWindow::~MainWindow()
{
    delete ui;
}

 void MainWindow::on_pushButton_2_clicked()
{
   QString text=ui->textEdit->toPlainText();      // you create a string object here
   QTableWidgetItem *item=table.item(rowname , 1);       // you do not create an object here, you basically store the pointer
   if (item)
       item->setText(text);
   else
      qDebug() << "check rowname!!";
   ++rowname ;
}

Note: this may work. It is not tested at all. Just brain to keyboard.

A friendly recommendation: I would propose to go through some tutorials in C++. You do not do yourself a favor by too much trial and error. You need to get at least a basic understanding there.

VRonin

@koahnig said in Object of QTableWidget:

int row = 1; // no possible this way

It is possible in C++11 but I did not find 1 person yet that thinks it's a good idea. I guess it's acceptable only if you have a lot of constructors and they all must initialise the member to the same value

@koahnig said in Object of QTableWidget:

A friendly recommendation: I would propose to go through some tutorials in C++. You do not do yourself a favor by too much trial and error. You need to get at least a basic understanding there.

I couldn't agree more

koahnig

@VRonin

Thanks for adding this comment. I was not completely aware of this detail. Now after your comment there seem to be a faint memory. ;)

For simple variables this is acceptable, but I am not sure either, if it is a good idea. Latest with the assignment of the table, there should be a problem, because you would need a call to the new operator. Or am I wrong there as well?

Armin

Thanks all
My problem is solved