Write new data into QTableWidgetItem, convert float into QTableWidgetItem

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Hello!

this is the code, I wrote:

Code:

#include "widget.h"
 
Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    this->setGeometry(30,30,800,750);
    rank = new QLineEdit("Enter the Rank", this);//rank->setGeometry(10,0,20,20);
    ok = new QPushButton("Ok", this); ok->setGeometry(150, 0,80,30);
    calculate = new QPushButton("calculate",this); calculate->setGeometry(250,0,80,30);
 
    coppy = new QTableWidgetItem;
 
    connect(ok,SIGNAL(clicked()),this,SLOT(ok_clicked()));
    connect(calculate,SIGNAL(clicked()),this,SLOT(calculate_clicked()));
}
 
Widget::~Widget()
{
 
}
 
void Widget::ok_clicked()  
{
 
   rank_of_Matrix = rank->text().toDouble(); 
   tbl=new QTableWidget(rank_of_Matrix,rank_of_Matrix,this);
   tbl->setGeometry(20,50,770,250);
   tbl->show();                     
 
    tbl->setItem(2,2,ptwi = new QTableWidgetItem(QString::number(40)));  
 
 
   Action_toArray(); // wrote all information into Array A[i][j] and make 0 all elements equals to zero
 
}
 
void Widget::calculate_clicked() 
{
    tbl  = new QTableWidget(rank_of_Matrix,rank_of_Matrix,this); 
 
    tbl ->setGeometry(20,350,770,250);  
    tbl->setItem(2,2, coppy->clone());   
    tbl ->show();                       
}
 
void Widget::Action_toArray()
{
 
    A= new float* [rank_of_Matrix]; 
    for(int i=0;i<rank_of_Matrix;i++){
        A[i]=new float [rank_of_Matrix];
    }
 
    for(int i=0;i<rank_of_Matrix;i++){
        for(int j=0;j<rank_of_Matrix;j++){
             //wrote into Array from QTableWidget
            A[i][j] = tbl->item(i,j)->data(Qt::DisplayRole).toFloat();
        }
    }
 
//make all elements equals to 2 
    for(int i=0;i<rank_of_Matrix;i++){
        for(int j=0;j<rank_of_Matrix;j++){
           if(A[i][j]==2){
               A[i][j]=0;
           }
        }
    }
}

My question is: how to write changed Array into Table2 after clicking button "Calculate"? Do I get it right that I need to convert float into QTableWidgetItem and then using command tbl->setItem(rank_of_Matrix,rank_of_Matrix, coppy->clone()); in loop write it into Table?

Thank you in advance!

17th July 2016, 10:42
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Quote:

Originally Posted by Blitzor DDD

My question is: how to write changed Array into Table2 after clicking button "Calculate"?

You only have one table, "tbl"

Quote:

Originally Posted by Blitzor DDD

Do I get it right that I need to convert float into QTableWidgetItem

No, you format the number as a QString and set that as the table widget item's text.
You can additionally store the actual number through setData(), using Qt::EditRole.

Quote:

Originally Posted by Blitzor DDD

and then using command tbl->setItem(rank_of_Matrix,rank_of_Matrix, coppy->clone());

No, you just create a new QTableWidgetItem, passing the text as its constructor argument.

Quote:

Originally Posted by Blitzor DDD

in loop write it into Table?

yes

Cheers,
_
17th July 2016, 11:06
Blitzor DDD

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Quote:

You only have one table, "tbl"

I meant tbl of course. I am going to use the same tbl and created it on the Widget below. Is it possible?

Quote:

setData(), using Qt::EditRole.

but setDate() has type bool. http://doc.qt.io/qt-5/qabstractitemmodel.html#setData

Quote:

No, you just create a new QTableWidgetItem, passing the text as its constructor argument. You can additionally store the actual number through setData(), using Qt::EditRole.

Could you please provide an example?
17th July 2016, 12:07
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem
Quote:

Originally Posted by Blitzor DDD

I meant tbl of course. I am going to use the same tbl and created it on the Widget below. Is it possible?

If you want to create a new table every time the button is clicked and just keep the old table for viewing, sure, why not.

Quote:

Originally Posted by Blitzor DDD

but setDate() has type bool. http://doc.qt.io/qt-5/qabstractitemmodel.html#setData

That is a different setData(), but which of the three arguments is of type bool?
I see QModelIndex, QVariant and int.

Quote:

Originally Posted by Blitzor DDD

Could you please provide an example?

Sure, basic C++:
Code:

QTableWidgetItem *item = new QTableWidgetItem(text); item->setData(Qt::EditRole, value);
Cheers,
_

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

So, I tried this, but program goes out since I click "calculate"

Code:

#include "widget.h"
#include <QAbstractItemModel>
 
Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    this->setGeometry(30,30,800,750);
    rank = new QLineEdit("Enter the Rank", this);//rank->setGeometry(10,0,20,20);
    ok = new QPushButton("Ok", this); ok->setGeometry(150, 0,80,30);
    calculate = new QPushButton("calculate",this); calculate->setGeometry(250,0,80,30);
 
 
 
    connect(ok,SIGNAL(clicked()),this,SLOT(ok_clicked()));
    connect(calculate,SIGNAL(clicked()),this,SLOT(calculate_clicked()));
}
 
Widget::~Widget()
{
 
}
 
void Widget::ok_clicked()  
{
 
   rank_of_Matrix = rank->text().toDouble();  
   tbl=new QTableWidget(rank_of_Matrix,rank_of_Matrix,this); 
   tbl->setGeometry(20,50,770,250);  
   tbl->show();                      
}
 
void Widget::calculate_clicked()  
{
    tbl_2  = new QTableWidget(rank_of_Matrix,rank_of_Matrix,this);  
 
    tbl_2 ->setGeometry(20,350,770,250);   
    Action_toArray(); 
    tbl_2 ->show(); 
}
 
void Widget::Action_toArray()
{
 
    A= new float* [rank_of_Matrix];  
    for(int i=0;i<rank_of_Matrix;i++){
        A[i]=new float [rank_of_Matrix];
    }
 
//read from Table 1 tbl
    for(int i=0;i<rank_of_Matrix;i++){
        for(int j=0;j<rank_of_Matrix;j++){
 
           A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat();
        }
    }
 
    //operation with Array 
    for(int i=0;i<rank_of_Matrix;i++){
        for(int j=0;j<rank_of_Matrix;j++){
           if(A[i][j]==2)
           {
               A[i][j]=0;
           }
        }
    }
 
    //write to Table2    tbl_2 
    QVariant tableData;
    for(int i=0;i<rank_of_Matrix;i++){
        for(int j=0;j<rank_of_Matrix;j++){
         tableData = A[i][j];
         tbl_2->item(i,j)->setData(Qt::EditRole,tableData);
        }
    }
}

So, could you please tell me what is wrong and how I can fix it?

17th July 2016, 12:52
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

You are accessing tbl->item(i, j), where did you create these items?
You are also accessing tbl_2->item(i, j), where did you create these items?

Cheers,
_

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

I thought, that item is a function to access to element of the Table and this is not an object to create it, isn't it?

this is header-file

.h

Code:

#ifndef WIDGET_H
#define WIDGET_H
 
#include <QWidget>
#include <QTableWidget>
#include <QLabel>
#include <QLineEdit>
#include <QPushButton>
#include <QTableWidgetItem>
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    Widget(QWidget *parent = 0);
    ~Widget();
 
private:
    QTableWidget     * tbl;         
    QTableWidgetItem * ptwi = 0;
    QTableWidgetItem * coppy;
    QStringList      * lst;       
    QLineEdit        * rank;
    QPushButton      * ok;
    QPushButton      * calculate;
 
    int rank_of_Matrix=1;
    float x=0;
    float **A;
 
 
private slots:
    void ok_clicked();
    void calculate_clicked();
    void Action_toArray();
};
 
#endif // WIDGET_H

17th July 2016, 14:01
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Quote:

Originally Posted by Blitzor DDD

I thought, that item is a function to access to element of the Table and this is not an object to create it, isn't it?

QTableWidget::item():

Quote:

Returns the item for the given row and column if one has been set; otherwise returns 0.

You don't seem to set items anywhere, so it is most likely that you are getting a null pointer back.
You don't check for "not null" so your crash is very likely the attempted dereferencing of that null pointer.

Cheers,
_
17th July 2016, 14:38
Blitzor DDD

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem
Ok, I added line in .h
QTableWidgetItem * item;
and in .cpp
item = new QTableWidgetItem();

but nevetherless, here:
Code:

for(int i=0;i<rank_of_Matrix;i++){ for(int j=0;j<rank_of_Matrix;j++){ //Ð·Ð°Ð¿Ð¸ÑÐ°Ð»Ð¸ Ð² Ð¼Ð°ÑÑÐ¸Ð² Ñ‚Ð¾, Ñ‡Ñ‚Ð¾ ÐµÑÑ‚ÑŒ Ð² Ñ‚Ð°Ð±Ð»Ð¸Ñ†Ðµ 1 A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat(); qDebug() <<"Ð"<<i<<" "<<j<<" = "<<A[i][j]; } }
I checked with qDebug() and it worked, data has been set into Array

and item in this loop has nothing to do with item connected to QTableWidget....

So, I still have no idea what is going on and what should I do with that...
Could you please tell me again?
17th July 2016, 15:14
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem
Quote:

Originally Posted by Blitzor DDD

Ok, I added line in .h
QTableWidgetItem * item;

And you did this why?

Quote:

Originally Posted by Blitzor DDD

and in .cpp
item = new QTableWidgetItem();

So you have a single tabel widget item stored in a member of the class.
How will that help solve your problem?
Quote:
Originally Posted by Blitzor DDD

Code:

for(int i=0;i<rank_of_Matrix;i++){ for(int j=0;j<rank_of_Matrix;j++){ //Ð·Ð°Ð¿Ð¸ÑÐ°Ð»Ð¸ Ð² Ð¼Ð°ÑÑÐ¸Ð² Ñ‚Ð¾, Ñ‡Ñ‚Ð¾ ÐµÑÑ‚ÑŒ Ð² Ñ‚Ð°Ð±Ð»Ð¸Ñ†Ðµ 1 A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat(); qDebug() <<"Ð"<<i<<" "<<j<<" = "<<A[i][j]; } }

I checked with qDebug() and it worked, data has been set into Array
Oh, maybe you have manually entered data into that table?

Quote:

Originally Posted by Blitzor DDD

So, I still have no idea what is going on and what should I do with that...
Could you please tell me again?

Check the stack trace of your program when it crashes.

I am pretty sure it crashes in
Code:

tbl_2->item(i,j)->setData(Qt::EditRole,tableData);
because you are calling setData() on a null pointer.

Cheers,
_
17th July 2016, 15:17
Blitzor DDD

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Yes, you are right.
And yes I enter it manually.

Problem was solved when I changed problem line to:
tbl_2->setItem(i,j, ptwi = new QTableWidgetItem(QString::number( A[i][j] )));
17th July 2016, 16:05
d_stranz

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

@BlitzorDDD: You could save yourself a lot of time and head-pounding if you used Google and looked up some of the many, many examples on how to use QTableWidget:

https://wiki.qt.io/How_to_Use_QTableWidget
http://www.codeprogress.com/cpp/libr...m=QTableWidget

and you would make many fewer mistakes if you learned how to write a good Qt application by studying the examples and tutorials on the Qt web site:

http://doc.qt.io/qt-5/qtexamplesandtutorials.html

We could spend many hours fixing each new bug you create, or you could teach yourself not to make bugs in the first place.
17th July 2016, 16:17
Blitzor DDD

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Yes, yes, I would and I will.
This is just my third program on Qt.
Thank you very much for your links!
17th July 2016, 16:20
anda_skoa

Re: Write new data into QTableWidgetItem, convert float into QTableWidgetItem

Quote:

Originally Posted by Blitzor DDD

Yes, you are right.
And yes I enter it manually.

Which, unsurprisingly, results in items being added to the table.
Your tbl_2, on the other hand, remains empty.

Quote:

Originally Posted by Blitzor DDD

Problem was solved when I changed problem line to:
tbl_2->setItem(i,j, ptwi = new QTableWidgetItem(QString::number( A[i][j] )));

Not sure what you have the "ptwi" in there for, but yes.
As already clarified in comment #2, btw.

Cheers,
_