4. QTableWidget Operations over columns

QTableWidget Operations over columns


  • Gents;

    Does anybody have an exemple of how to make a column 3 of a table as the result of the multiplicaion of 2 other columns: Column 1 X column 2.

    Cheers;

    Raouf

    0
  • Moderators

    Sure, here you go:

    connect(&tableWidget, &QTableWidget::itemChanged, &tableWidget, [](QTableWidgetItem* item)
{
    if (item->column() == 0 || item->column() == 1)
    {
        auto other_item  = item->tableWidget()->item(item->row(), (item->column() + 1)%2);
        auto result_item = item->tableWidget()->item(item->row(), 2);

        int val1 = item->data(Qt::DisplayRole).toInt();
        int val2 = other_item->data(Qt::DisplayRole).toInt();

        result_item->setData(Qt::DisplayRole, val1 * val2);
    }
});

    Make sure you add necessary error checking (eg. are the values numbers and things like that) and make the 3rd column read only.
    I left that out as an exercise ;)

    4 2 Replies

  • @Chris-Kawa
    Thas was a hard exercice. I think this is a signal, I don t see the slot though!! I tried to implement that and I get the following error message:

    E:\Computing\Qt Designer\cfadvisor.cpp:191: erreur : no matching function for call to 'CFAdvisor::connect(QTableWidget**, void (QTableWidget::)(QTableWidgetItem), QTableWidget**, CFAdvisor::setupTableItems()::<lambda(QTableWidgetItem*)>)'
    });
    ^
    Thanks

    0
  • Lifetime Qt Champion

    Hi,

    From the look of your error, you are passing the address of the pointer to your QTableWidget item object. Remove the & before it and your should be good to go.

    2

  • @Chris-Kawa
    Sir; I got this code; there's no error message and the window pops up but the column 3 does not calculate the result value. Please advise.

    ui(new Ui::CFAdvisor)
    {
    ui->setupUi(this);

    ui->m_ptable_ConvDesign->setItem(0, 0, new QTableWidgetItem("Pre-PAD"));
ui->m_ptable_ConvDesign->setItem(1, 0, new QTableWidgetItem ("PAD"));

    for (int row = 2; row < ui->m_ptable_ConvDesign->rowCount()-9; ++row)
    {
        for (int column = 1; column < ui->m_ptable_ConvDesign->columnCount(); ++column)
        {
         ui->m_ptable_ConvDesign->setItem(row, 0, new QTableWidgetItem ("SLF"));
        }
    }
ui->m_ptable_ConvDesign->setItem(10, 0, new QTableWidgetItem ("Flush"));

for (int row = 0; row < ui->m_ptable_ConvDesign->rowCount(); ++row)
{
    for (int column = 0; column < ui->m_ptable_ConvDesign->columnCount(); ++column)
    {
        connect(m_ptable_ConvDesign, &QTableWidget::itemChanged, m_ptable_ConvDesign, [](QTableWidgetItem* item)
            {
                if (item->column() == 1 || item->column() == 2)
                {
                    auto CleanVol_item  = item->tableWidget()->item(item->row(), (item->column() + 1)%2);
                    auto PropVol_item = item->tableWidget()->item(item->row(), 3);

                    double val1 = item->data(Qt::DisplayRole).toDouble();
                    double val2 = CleanVol_item->data(Qt::DisplayRole).toDouble();

                    PropVol_item->setData(Qt::DisplayRole, val1 * val2);
                }
            });
    }
}

    }

    0
  • Moderators

    There are many problems in your code. Where to start?...

    I'm not sure you're aware that C++ uses 0-based indexing. Column 3 is thus item->column() == 2. So if you want to multiply first and second column and store in third then you multiply index 0 with index 1 and store in index 2.

    Next, In your first for loop you only put items in column 0, so if you try to access any other column (either read or write) your app will crash. Put empty items in columns 1 and 2 if you don't want to fill them at startup.

    Next, you should only make the connect once, not for every cell in the table! Now you have dozens of identical connections firing when you change a single value.

    Here connect(m_ptable_ConvDesign, &QTableWidget::itemChanged, m_ptable_ConvDesign, [](QTableWidgetItem* item) you're missing ui-> before both m_ptable_ConvDesign. If it compiles you have something wrong in your code because m_ptable_ConvDesign would have to be a local variable.

    As mentioned before if (item->column() == 1 || item->column() == 2) will match second and third column, not first and second.

    This trick (item->column() + 1)%2 only works for 0 and 1: (0+1)%2 = 1, (1+1)%2 = 0. For values 1 and 2 in your code it results in garbage: (1+1)%2 = 0, (2+1)%2 = 1. If you're not comfortable with modulo arithmetic just use a branch expression: (item->column() == 1) ? 2 : 1.

    As mentioned above this item->tableWidget()->item(item->row(), 3); gets an item in fourth column, not third.

    4 3 Replies

  • @Chris-Kawa
    For now; I would like to confirm the columns assignments:

    I am using the first column as an indicator of the stage type; the second and the third are input data and the fourth in the result.

    Thanks for your comments. Let me make the changes and I will let you know.

    Cheers;

    Raouf

    0

  • @Chris-Kawa
    Thank you man for your support. The code is working and is described below for those who wand to do the same:

    ui(new Ui::CFAdvisor)
    {
    ui->setupUi(this);

    ui->m_ptable_Conv->setItem(0, 0, new QTableWidgetItem("Type1"));
ui->m_ptable_Conv->setItem(1, 0, new QTableWidgetItem ("Type2"));

    for (int row = 2; row < ui->m_ptable_Conv->rowCount()-9; ++row)
    {
        for (int column = 0; column < ui->m_ptable_Conv->columnCount(); ++column)
        {
         ui->m_ptable_Conv->setItem(row, 0, new QTableWidgetItem ("Type3"));
        }
    }
ui->m_ptable_Conv->setItem(10, 0, new QTableWidgetItem ("Type4"));

for (int row = 0; row < ui->m_ptable_Conv->rowCount(); ++row)
{
    for (int column = 1; column < ui->m_ptable_Conv->columnCount(); ++column)
    {
        QTableWidgetItem *newItem = new QTableWidgetItem();
        ui->m_ptable_Conv->setItem(row, column, newItem);
    }
}
    connect(ui->m_ptable_Conv, &QTableWidget::itemChanged, ui->m_ptable_Conv, [](QTableWidgetItem* item)
            {
                if (item->column() == 1 || item->column() == 2)
                {
                    auto Input1_item  = item->tableWidget()->item(item->row(), 1);
                    auto Input2_item  = item->tableWidget()->item(item->row(), 2);
                    auto Result_item = item->tableWidget()->item(item->row(), 3);

                    double val1 = Input1_item->data(Qt::DisplayRole).toDouble();
                    double val2 = Input2_item->data(Qt::DisplayRole).toDouble();

                    Result_item->setData(Qt::DisplayRole, val1 * val2);
                }
            });
    0

  • @Chris-Kawa
    I have a new challenge and I am wondering if you have time to help out. I want to caluculate column 5 which is the result of Column 3 + (factor * Column 4).
    The factor is a static input outside the table. The error I had were: the factor is not captured and is a static.

    Your support is welcome.

    Cheers;

    Raouf

    0 1 Reply
  • Qt Champions 2019

    @Abderaouf Why don't you show the code?
    How exactly is this static factor declared and where?

    0
  • Moderators

    The error says it all: you need to capture the value before you can use it inside a lambda. For example if the input is a global static like this static int foo = 42; you would capture a reference to it like this:[&foo](QTableWidgetItem* item)

    2 1 Reply

  • @Chris-Kawa

    below is the code I came up with. @jsulm the static factor is declared in a groupe box in the first tab and is copied in another groupe box in the second tab where the table is so the user can know what factor he s using without going back and forth, the factor is not a global static one. The calculation is done but with a wrong result: colulmn 5 = colulmn 3 without the additional factor * column 4. I am pretty sure there is a mistake in the declaration.

    Cheers;

    Raouf

    static double AVF = ui->Input_PropAVF->text().toDouble();
    ui->label_PropAVF1->setText(QString::number(AVF));

        connect(ui->m_ptable_ConvDesign, &QTableWidget::itemChanged, ui->m_ptable_ConvDesign, [&AVF](QTableWidgetItem* item)
               {
               if (item->column() == 2 || item->column() == 3)
                {
                    auto CleanVol_item  = item->tableWidget()->item(item->row(), 2);
                    auto PropVol_item = item->tableWidget()->item(item->row(), 3);
                    auto SlurryVol_item  = item->tableWidget()->item(item->row(), 4);

                    double val1 = CleanVol_item->data(Qt::DisplayRole).toDouble();
                    double val2 = PropVol_item->data(Qt::DisplayRole).toDouble();

                    SlurryVol_item->setData(Qt::DisplayRole, (AVF * val2) + val1);
                }
            });
    0
  • Moderators

    Aww, that doesn't look right.
    Why do you use a text input widget when you want a number? Using text to store a double is just weird. Better use something like QDoubleSpinBox and then you get the double value directly.
    You don't need a static variable to pass it to that lambda. I only gave that example because you said you have a static input, which you don't really seem to.
    Just capture this by reference and use the value directly:

    [&](QTableWidgetItem* item) {
    ...
    SlurryVol_item->setData(Qt::DisplayRole, (ui->Input_PropAVF->text().toDouble() * val2) + val1);
}

    If you used a proper QDoubleSpinBox it would be like this:

    [&](QTableWidgetItem* item) {
    ...
    SlurryVol_item->setData(Qt::DisplayRole, (ui->Input_PropAVF->value() * val2) + val1);
}
    1 2 Replies

  • @Chris-Kawa Wow, this is a kids game for you isn't it. I regret I didn t study this when I had the chance.

    Thanks man

    0

  • @Chris-Kawa , hello man;

    I have a new challenge, hope this is the last.

    The next operation I need to do is calculating the items of a given column, column 4, of a given table, m_ptable_Conductor, from a column 4 of another table, m_ptable_ConvDesign, using a value storedd in QLineEdit; as follows:
    SlurryVolCond_item->setData(Qt::DisplayRole, qRound(val1 * (ui->Input_DesSLF-> text().toDouble())));

    The results will populate the column of table 2 upon click on a push button.

    I have prepared the below code, there's no error but nothing is changing in table 2.

    void CFAdvisor::on_Button4_clicked()
{
    connect(ui->m_ptable_Conductor, &QTableWidget::itemChanged, ui->m_ptable_ConvDesign, [&](QTableWidgetItem* item)
               {
               if (item->column() == 4)
                {
                    auto SlurryVolConv_item = ui->m_ptable_ConvDesign->item(item->row(), 4);
                    auto SlurryVolCond_item  = item->tableWidget()->item(item->row(), 4);

                    double val1 = SlurryVolConv_item->data(Qt::DisplayRole).toDouble();
                    
                    SlurryVolCond_item->setData(Qt::DisplayRole, qRound(val1 * (ui->Input_DesSLF-> text().toDouble())));

                   
                    }

            });
}

    Thanks

    0
  • Lifetime Qt Champion

    Hi
    Put a breakpoint at
    if (item->column() == 4)
    and single step from there. You can then see what values u take etc.

    0 1 Reply

  • @mrjj
    Thanks mrjj. I think I fixed that based on Chris-kawa previous comments. I have another issue. I want to creat a Qpushbutton that fill the items of the second table based on the data of the first table using an if condition that check the QString of the 2nd column. If the value is "Y", the calculation should be on one way and if the value is "N" the calculation are done in another way. The code is not showing any error but .exe is crashing when I push the button. below is my code, thanks for reviewing it and advising:

    void CFAdvisor::on_Button4_clicked()
    {
    QString str1;
    QString str2 = "Y";
    QString str3 = "N";

      for (int row = 0; row < ui->m_ptable_ConvDesign->rowCount(); ++row)
      {
          QTableWidgetItem *stagepulse_item = ui->m_ptable_ConvDesign->item(row, 1);
          str1 = stagepulse_item->data(Qt::DisplayRole).toString();
      }

    for (int column = 0; column < ui->m_ptable_Conductor->columnCount(); ++column)
    {
      for (int row = 0; row < ui->m_ptable_Conductor->rowCount(); ++row)
      {
          if (str1 == str2)
           {

        QTableWidgetItem *PropConCond_item = ui->m_ptable_Conductor->item(row, 1);
        QTableWidgetItem *PropConConv_item = ui->m_ptable_ConvDesign->item(row,2);
        PropConCond_item->setData(Qt::DisplayRole,PropConConv_item->text().toDouble());

        QTableWidgetItem *SlurryVolCond_item = ui->m_ptable_Conductor->item(row, 4);
        QTableWidgetItem *SlurryVolConv_item = ui->m_ptable_ConvDesign->item(row,5);
        SlurryVolCond_item->setData(Qt::DisplayRole,qRound(((ui->Input_DesSLF-> text().toDouble())) * (SlurryVolConv_item->text().toDouble())));

        QTableWidgetItem *CleanVolCond_item = ui->m_ptable_Conductor->item(row, 2);
        CleanVolCond_item->setData(Qt::DisplayRole,qRound((SlurryVolCond_item->text().toDouble()) / ( 1 + ((ui->label_PropAVF1->text().toDouble()) * (PropConCond_item->text().toDouble())))));

           }

           if (str1 == str3)
           {

        QTableWidgetItem *PropConCond_item = ui->m_ptable_Conductor->item(row, 1);
        QTableWidgetItem *PropConConv_item = ui->m_ptable_ConvDesign->item(row,2);
        PropConCond_item->setData(Qt::DisplayRole,PropConConv_item->text().toDouble());

        QTableWidgetItem *SlurryVolCond_item = ui->m_ptable_Conductor->item(row, 4);
        QTableWidgetItem *SlurryVolConv_item = ui->m_ptable_ConvDesign->item(row,5);
        SlurryVolCond_item->setData(Qt::DisplayRole,SlurryVolConv_item->text().toDouble());

        QTableWidgetItem *CleanVolCond_item = ui->m_ptable_Conductor->item(row, 2);
        CleanVolCond_item->setData(Qt::DisplayRole,qRound((SlurryVolCond_item->text().toDouble()) / ( 1 + ((ui->label_PropAVF1->text().toDouble()) * (PropConCond_item->text().toDouble())))));

           }
        }
    }
}

    Regards;

    Raouf

    0
  • Lifetime Qt Champion

    Hi
    You should check all pointer to QTableWidgetItem * before using them.
    It might return NULL and u crash.

    Still if you place a break point and single step you should find the line that makes you crash.

    0 1 Reply

  • @mrjj I think it is that line, where I convert a QtableWidgetItem to QString:

    str1 = stagepulse_item->data(Qt::DisplayRole).toString();

    The syntax is right, I dont know what is the real reason though.

    0 2 Replies
  • Lifetime Qt Champion

    @Abderaouf
    It seems correct. You are getting a QVariant from data and call toString.
    So when debugging it crash on this line?

    0 1 Reply

  • @Abderaouf said in QTableWidget Operations over columns:

    I dont know what is the real reason though

    probably stagepulse_item is a null pointer

    also your logic does not work, at the moment the calculation is based on whether the last line, second column in m_ptable_ConvDesign is Y or N

    1 1 Reply

  • @mrjj When I run it, it works until I click on the button and then It crashes even though all the data are input. when I take out this line, the button doesn't work when I click at it.

    0 1 Reply
  • Lifetime Qt Champion

    @Abderaouf
    as @VRonin asks,
    could stagepulse_item be NULL ?

    1

  • @VRonin how can I check if stagepulse_item is a null pointer??
    I want to check the value of each line not only the last. I should probably add another for loop for the columns, right??

    0 1 Reply
  • Lifetime Qt Champion

    @Abderaouf

    if ( ! stagepulse_item) {
    qDebug () << "NULL !!!";
    return;
    }

    str1 = stagepulse_item->data(Qt::DisplayRole).toString();
    ...

    • I want to check the value of each line not only the last. I should probably add another for loop for the columns, right??

    yes something like that. currently u loop m_ptable_ConvDesign first and set str1 but that should be checked
    while u loop over the rows. So for a row if COL have Y/N then do it accordingly.

    2 1 Reply

  • @mrjj

    I used the below and it worked fine:

    QTableWidgetItem *stagepulse_item = ui->m_ptable_ConvDesign->item(row, 1);
    if(stagepulse_item!=NULL)
    {
    str1 = stagepulse_item->data(Qt::DisplayRole).toString();
    }

    Cheers;

    1

  • Gents;

    One more challenge. I am trying to create a menu in my QTabWidget using the below basic code:

    void CFAdvisor::CreateMenu()

    {
    fileMenu = MenuBar().addMenu(tr("&File"));
    fileMenu->addAction(actionExit);
    fileMenu-> addAction(actionPrint);
    helpMenu = MenuBar() ->addMenu(tr("&Help"));
    helpMenu-> addAction(actionContent);
    helpMenu-> addAction(actionAbout);

    }

    I have a the error message though, it says the following:

    C:\computing\Qt Designer\cfadvisor.cpp:488: error: 'menuBar' was not declared in this scope
    fileMenu = menuBar()->addMenu(tr("&File"));
    ^

    Any advise on how to correct this error. this is the Qt version I have.

    0_1483725857061_upload-e59f0784-f714-4f46-8b9d-31dd599923a6

    Cheers

    0
  • Lifetime Qt Champion

    Hi
    Where is MenuBar() ?
    if CFAdvisor is not a main window type then you need to create the MenuBar yourself if not already
    added in Designer.

    http://www.codeprogress.com/cpp/libraries/qt/QMenuBarAddMenu.php

    0
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