Write new data into QTableWidgetItem, convert float into QTableWidgetItem

[Blitzor DDD]

Hello!

this is the code, I wrote:


#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(calc ulate_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!

[anda_skoa]

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

You only have one table, "tbl"



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.




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.



in loop write it into Table?

yes

Cheers,
_

[Blitzor DDD]

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?


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


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?

[anda_skoa]

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.



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.



Could you please provide an example?
Sure, basic C++:


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


Cheers,
_

[Blitzor DDD]

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


#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(calc ulate_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?

[anda_skoa]

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,
_

[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?

this is header-file

.h

#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

[anda_skoa]

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():


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,
_

[Blitzor DDD]

Ok, I added line in .h
QTableWidgetItem * item;
and in .cpp
item = new QTableWidgetItem();

but nevetherless, here:


for(int i=0;i<rank_of_Matrix;i++){
for(int j=0;j<rank_of_Matrix;j++){
//записали в массив то, что есть в таблице 1
A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat();
qDebug() <<"А"<<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?

[anda_skoa]

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

And you did this why?



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?




for(int i=0;i<rank_of_Matrix;i++){
for(int j=0;j<rank_of_Matrix;j++){
//записали в массив то, что есть в таблице 1
A[i][j] = tbl->item(i,j)-> data(Qt::DisplayRole).toFloat();
qDebug() <<"А"<<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?



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


tbl_2->item(i,j)->setData(Qt::EditRole,tableData);

because you are calling setData() on a null pointer.

Cheers,
_

[Blitzor DDD]

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] )));

[d_stranz]

@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/libraries/qt/qtClasses.php?item=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.

[Blitzor DDD]

Yes, yes, I would and I will.
This is just my third program on Qt.
Thank you very much for your links!

[anda_skoa]

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.



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,
_