[Solved] Subclassing QAbstractTableModel

ninio

I have got implemented all the virtual function than subclassing QAbstractTableModel needs, anyway I can't see anything. Just an empty table.

I made a simple example which reproduces this issues:
@#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QAbstractTableModel>

namespace Ui {
class MainWindow;
}

//////////////////////////////////////////////////
/// \brief The MainWindow class
class MainWindow : public QMainWindow
{
Q_OBJECT

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

private:
Ui::MainWindow *ui;
};

//////////////////////////////////////////////////
/// \brief The ThreadModel class
class ThreadModel : public QAbstractTableModel
{
Q_OBJECT

public:
explicit ThreadModel(QObject *parent = 0);
~ThreadModel();

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 override;

protected:
QList<QList<int>> threadList;
};

#endif // MAINWINDOW_H
@

@#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <sstream>
using namespace std;

////////////////////////////////////////////////
/// \brief The ThreadDetail class
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);

ThreadModel model;
ui->tableView->setModel(&model);

}

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

//////////////////////////////////////////////////
/// \brief The ThreadModel class
ThreadModel::ThreadModel(QObject parent/ = 0*/)
{
QList<int> column1;
column1.push_back(10);
column1.push_back(20);
column1.push_back(30);
column1.push_back(40);

threadList.push_back(column1);

QList<int> column2;
column2.push_back(50);
column2.push_back(60);
column2.push_back(70);
column2.push_back(80);

threadList.push_back(column2);

}

ThreadModel::~ThreadModel()
{
}

int ThreadModel::rowCount(const QModelIndex&/* parent*/) const
{
return threadList[0].size();
}

int ThreadModel::columnCount(const QModelIndex&/* parent*/) const
{
return threadList.size();
}

QVariant ThreadModel::data(const QModelIndex &index, int role) const
{
if (role == Qt::DisplayRole)
return threadList[index.column()][index.row()];

return QVariant::Invalid;

}

QVariant ThreadModel::headerData(int section, Qt::Orientation orientation, int role) const
{
if (role == Qt::DisplayRole)
{
stringstream ss;
if (orientation == Qt::Horizontal)
{
ss << "H_" << section;
return QString(ss.str().c_str());
}
else if (orientation == Qt::Vertical)
{
ss << "H_" << section;
QString debug = QString(ss.str().c_str());
return QString(ss.str().c_str());
}
}

return QVariant::Invalid;

}
@

What else do I need to do? :S

SGaist

Hi,

If the role is not something you handle, return the base class function's implementation otherwise your view won't have any information to show you anything

ninio

What do you mean with "handling the rol"? What else do I need to do?

SGaist

@ if (role == Qt::DisplayRole)@

You only handle DisplayRole, returning QVariant::Invalid for every other role just gives the views nothing to work on.

What to do ? What I already wrote, for every other role return the base class implementation result of data and headerData

ninio

First, you CAN'T to return the base class implementation, because it's PURE virtual. You know, the data function is = 0.
And second, even no handling the rol (without condition) it shows nothing.

SGaist

Yes you can. You can have have a pure virtual function with a default implementation which is not the case for QAbstractTableModel.

Anyway, you are missing some checks like e.g. the validity for the index given as a parameter. Did you also ensure that all your methods are called ?

You can have a look at the Pixelator example, it uses a custom QAbstractTableModel

ninio

Let's see if we are talking about the same. If we have:
@#include <iostream>
using namespace std;

class A
{
public:
virtual void foo() = 0; // Now, you NEED to override this method!
};

void A::foo()
{
cout << "A::foo" << endl;
}

class B : public A
{
public:
void foo() override; // Overriding base foo. You get a compiling error if not!:
// Cannot declare variable 'b' to be of abstract type 'B' B b; because the following virtual functions are pure within 'B'
};

void B::foo()
{
cout << "B::foo" << endl;
}

int main(int argc, char *argv[])
{
B b;

b.foo();

return 0;

}@

As I said before, I can't to call a pure virtual function (=0). You need to override it on its derived class.

yetanotherbender

I stumbled upon a similar problem when reading the "Model/View Tutorial":http://qt-project.org/doc/qt-5/modelview.html . One of your problem(s) might be, that you create a Stack-variable "model" in your MainWindow constructor, which you then pass to the tableView as model. When the constructor is done, the Stack-variable won't exist anymore.

You could try allocating "model" on the heap and see if this is fixing your problem. I.e. change

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

ThreadModel model;
ui->tableView->setModel(&model);

}@

... to ...

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

ThreadModel *model = new ThreadModel();
ui->tableView->setModel(model);

}@

SGaist

yetanotherbender has the right solution, I missed that one in your code.

As for our little understanding problem:

@
#include <iostream>
using namespace std;

class A
{
public:
virtual void foo() = 0; // Now, you NEED to override this method! << Correct and agreed
};

void A::foo()
{
cout << "A::foo" << endl;
}

class B : public A
{
public:
void foo() override; // Overriding base foo. You get a compiling error if not!: << still correct and agreed
};

void B::foo()
{
A::foo() // If your B class doesn't do anything special you can call the base class default implementation
}

int main(int argc, char *argv[])
{
B b;

b.foo();

return 0;

}
@

ninio

[quote author="yetanotherbender" date="1403608883"]You could try allocating “model” on the heap and see if this is fixing your problem[/quote]

Great! That fixed the problem! Thank you SO F*much!! :D

SGaist, thank you for trying and being pacient!! :)

SGaist

You're welcome !

Happy Qt coding ! :)