Questions regarding QAbstractTableModel and QDataWidgetMapper

BadPistol97

I was able to show a single row of data in a tableView and then I was trying to use QDataWidgetMapper to map the data both on a tableView and lineEdit. So that when I change the data in lineEdit, the table will reflect the changes as well (am I right about the function of QDataWidgetMapper here?)

Code of constructing a model for Table and Mapping:

amodel.h

#ifndef AMODEL_H
#define AMODEL_H
#include <QAbstractTableModel>

class aModel:public QAbstractTableModel
{
    Q_OBJECT

public:
    aModel(QObject *parent = nullptr);

     // to add data to the model
    void populateData(const QList<QString> &contactName,const QList<QString> &contactPhone);

    int rowCount(const QModelIndex &parent = QModelIndex()) const override;

    int columnCount(const QModelIndex &parent = QModelIndex()) const override;

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;

    QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const Q_DECL_OVERRIDE;
 

private:
    QList<QString> tm_contact_name;
    QList<QString> tm_contact_phone;

};

#endif // AMODEL_H

amodel.cpp

#include "amodel.h"

aModel::aModel(QObject *parent) : QAbstractTableModel (parent)
{

}


// Create a method to populate the model with data:
void aModel::populateData(const QList<QString> &contactName,const QList<QString> &contactPhone)
{
    tm_contact_name.clear();
    tm_contact_name = contactName;
    tm_contact_phone.clear();
    tm_contact_phone = contactPhone;
    return;
}

int aModel::rowCount(const QModelIndex &parent) const{

    Q_UNUSED(parent);
    return tm_contact_name.length();
    //return 2;
}

int aModel::columnCount(const QModelIndex &parent) const{

    Q_UNUSED(parent);
    return 2;

    //return 3;
}

QVariant aModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid() || role != Qt::DisplayRole) {
        return QVariant();
    }
    if (index.column() == 0) {
        return tm_contact_name[index.row()];
    } else if (index.column() == 1) {
        return tm_contact_phone[index.row()];
    }
    return QVariant();
}

QVariant aModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    if (role == Qt::DisplayRole && orientation == Qt::Horizontal) {
        if (section == 0) {
            return QString("Name");
        } else if (section == 1) {
            return QString("Phone");
        }
    }
    return QVariant();
}

Mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QLabel>
#include <algorithm>
#include <QLineEdit>
#include <QDataWidgetMapper>
#include <QDebug>

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

    QList<QString> contactNames;
    QList<QString> contactPhoneNums;

    contactNames.append("Thomas");
    contactPhoneNums.append("123-456-7890");

    aModel *PhoneBookModel = new aModel(this);

    PhoneBookModel->populateData(contactNames,contactPhoneNums);

    ui->tableView->setModel(PhoneBookModel);

    ui->tableView->horizontalHeader()->setVisible(true);

    ui->tableView->show();

    QDataWidgetMapper *mapper = new QDataWidgetMapper;

    mapper->setOrientation(Qt::Horizontal);

    mapper->setModel(PhoneBookModel);

    mapper->addMapping(ui->lineEdit,0);

    mapper->addMapping(ui->lineEdit_2,1);

    mapper->toFirst();


}

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

This is the table and 2 lineEdits:

From the code, it seems like I have mapped the data in model to those lineEdits. Should the data have been shown in lineEdit? or it was not mapped at all?

VRonin

@BadPistol97 said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

Should the data have been shown in lineEdit?

No, you are missing 1 step (connecting the view to the mapper) described here: https://doc.qt.io/qt-5/qdatawidgetmapper.html#setCurrentModelIndex

P.S.
populateData is wrong. When you add/remove rows or change the content of the model you have to signal it. See https://doc.qt.io/QT-5/qabstractitemmodel.html#subclassing

SGaist

Hi,

Besides the point made by @VRonin, you are only returning something for DisplayRole you need to also do that for EditRole.

JonB

Not wanting to be too OT to the question. But: I have been using Qt model/views for two years and until now I had no idea that it had a QDataWidgetMapper class, so that I could link my view-tables to dedicated, distinct widgets for editing each row, which I need. Not knowing, I have written explicit, separate code for all these widgets. The only mention in the overview https://doc.qt.io/qt-5/model-view-programming.html I now see is in the The Model/View Classes list at the foot. I have not come across the class mentioned in all my reading about the views I use.

This is a shame :(

BadPistol97

@VRonin said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

No, you are missing 1 step (connecting the view to the mapper) described here: https://doc.qt.io/qt-5/qdatawidgetmapper.html#setCurrentModelIndex

Okay, now I added code:

QDataWidgetMapper *mapper = new QDataWidgetMapper;

    mapper->setOrientation(Qt::Horizontal);

    mapper->setModel(PhoneBookModel);
    
    // added this line 
    connect(ui->tableView->selectionModel(),SIGNAL(currentColumnChanged(QModelIndex,QModelIndex)),
            mapper,SLOT(setCurrentModelIndex(QModelIndex)));

    mapper->addMapping(ui->lineEdit,0);

    mapper->addMapping(ui->lineEdit_2,1);

    mapper->toFirst();

but it says:

VRonin

why did you use currentColumnChanged instead of currentRowChanged as suggested by the documentation?
the error you see has nothing to do with the code above, it refers dataChanged at line 362
Use the new connection syntax to have those errors checked at compile time and solved faster

BadPistol97

@SGaist said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

Besides the point made by @VRonin, you are only returning something for DisplayRole you need to also do that for EditRole.

I guessed you and @VRonin were referring this
bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override;

So I added the function like this in amodel.cpp:

bool aModel::setData(const QModelIndex &index, const QVariant &value, int role ){

    if(role == Qt::EditRole){
        if(!checkIndex(index))
            return false;

       QString m_gridData[this->rowCount()][this->columnCount()];

       m_gridData[index.row()][index.column()] = value.toString();

       QString result;

       for(int row = 0; row < this->rowCount(); row++){

           for(int col=0; col < this->columnCount(); col++)
               result += m_gridData[row][col] + " ";
       }

       emit editComplete(result);
       return true;
    }

    return false;

}

am I correct?

BadPistol97

@VRonin Alright, I have changed the line to:

connect(
        ui->tableView->selectionModel(),&QItemSelectionModel::currentRowChanged,
                mapper,&QDataWidgetMapper::setCurrentModelIndex);

the data in tableView is still not shown in those lineEdits though.

SGaist

@BadPistol97 said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

@SGaist said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

Besides the point made by @VRonin, you are only returning something for DisplayRole you need to also do that for EditRole.

I guessed you and @VRonin were referring this
bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override;

So I added the function like this in amodel.cpp:
// snip
am I correct?

No, you are wrong. I was talking about your "data" method.

Just return the same stuff for display and edit roles and you will be good to go.

VRonin

P.S. to @SGaist post:

Your setData implementation is wrong, you are not emitting dataChanged.
As with anybody approaching model/view programming, I always suggest, instead of subclassing a model which is quite hard, just use something like QAbstractItemModel* model = new QStandardItemModel(GiveMeAParent);. This way you can have a model that works out of the box and you can always change it later to something more efficient without changing existing code

BadPistol97

@SGaist

Alright, I have changed the if condition in
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override; to:
if (!index.isValid() || role != Qt::DisplayRole && Qt::EditRole)

Now the LineEdits show the data from tableView.

BadPistol97

@VRonin

@VRonin said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

just use something like QAbstractItemModel* model = new QStandardItemModel(GiveMeAParent);.

May I know what will be the parent here?

BadPistol97

@VRonin said in Questions regarding QAbstractTableModel and QDataWidgetMapper:

Your setData implementation is wrong, you are not emitting dataChanged

Okay, I have finally found a clear documentation about this:

And have changed the setData(const QModelIndex &index, const QVariant &value, int role) to:

bool aModel::setData(const QModelIndex &index, const QVariant &value, int role ){

    if(index.isValid() && role == Qt::EditRole){

        int row = index.row();
        
        // contacts is a c++ struct 
        auto contact = contacts.value(row);

        if (index.column() == 0)
              contact.name = value.toString();

        else if (index.column() == 1)
              contact.phone = value.toString();

        else
              return false;

        contacts.replace(row,contact);

        emit dataChanged(index,index,{role});

        return true;
    }

    return false;

}

Now the LineEdits can change the data of the tableView when new data is keyed in .

BadPistol97

Now if I want to add one more row to the table and 2 more lineEdits for the new row in the table:

How to map the new row to the new LineEdits by using the same mapper?

SGaist

Update the mapper current index.

BadPistol97

@SGaist

I found that no matter I put toFirst(), toNext(), or toLast() the LineEdits being mapped by the mapper always contain the data from the first row of the table.

    mapper->setOrientation(Qt::Horizontal);

    mapper->setSubmitPolicy(QDataWidgetMapper::ManualSubmit);

    mapper->setModel(PhoneBookModel);

    connect(
        ui->tableView->selectionModel(),&QItemSelectionModel::currentRowChanged,
                mapper,&QDataWidgetMapper::setCurrentModelIndex);

    mapper->addMapping(ui->lineEdit,0);
    mapper->addMapping(ui->lineEdit_2,1);

    mapper->toLast();

What did I do wrong?

SGaist

When are you adding data to your model ?

BadPistol97

@SGaist

I added data to the model before the tableView set to that model:

 aModel *PhoneBookModel = new aModel(this);

 PhoneBookModel->setContactsInfo("Thomas","123-456-7890");
 PhoneBookModel->setContactsInfo("Richard","222-333-4444");

 ui->tableView->setModel(PhoneBookModel);
 ui->tableView->horizontalHeader()->setVisible(true);
 ui->tableView->show();

Then I mapped the data of the model to lineEdits.

VRonin

Stop. Step back.
It looks like you want 2 labels and 2 line edits for each row in your model. Can I ask why?
You can edit the items directly inside the view, you don't need external editors

BadPistol97

@VRonin

I wanted to make something like this:

This is the page showing table

And another view to edit the record, so I would like to have each column of a row mapped to a lineEdit