Using QAbstractTableModel.parent

[Max Yaffe]

I've got a table model derived from QAbstractTableModel. I would like to create column objects within it using something like:

int MyTableModel::appendColumn(...)
{
Column * column = new Column(..., this->parent());
...
}

However this->parent() expects a QModelIndex parameter. I want to supply the parent object given to the MyTableModel when it was created, e.g.
model = new MyTableModel(..., parent);

How should I retrieve that original parent if model->parent() doesn't do it?

Or should I instead be making the model the parent of the column like:
Column * column = new Column(..., this);

Thanks for your help.
Max

[wysota]

I think you are mixing two things. When creating the model, you passed a QObject instance as a parent object of the model. The parent() method of the model is to return an index of an item which is a parent item (not parent widget) to the item passed as the argument. In case of table models it always returns an empty index (because items don't have parents).

Models don't have parent widgets, only widgets do. Models have parent objects which are only used to make sure the model gets deleted when it is no longer needed.

[Max Yaffe]

Ok, so how do I get the parent object?
Max

[wysota]

Use QObject::parent(), although I think you shouldn't need that. What are you trying to achieve?

[Max Yaffe]

Use QObject::parent(), although I think you shouldn't need that. What are you trying to achieve?

I'm trying to create a data table model out of data column objects where each column has a dynamically defined data type. Each column object should be managed by the Qt memory cleanup subsystem so it must derive from QObject and have the Q_OBJECT macro in it's class definition.

Here's my solution:

To add a column execute something like:
int MyTableModel::columnAppendNew(QString name)
{
MyColumn *column = new MyColumn(name, this);
columns_.append(column);
}

The MyColumn class looks like:
class MyColumn : public QObject
{
Q_OBJECT
public:
explicit MyColumn(QString header, QObject *parent = 0)
: header_(header), QObject(parent)
{
}
~AbstractColumn()
{
}
protected:
QString header_;
}

So now, I hope, the MyColumn object is created as a "memory child" of MyTable. N'est pas? Why MyTable is deleted, then all the columns will likewise be deleted.

Would someone please tell the trolls their dual usage of the term "parent" is confusing.

Thanks,
Max

[wysota]

Do you need to derive those columns from QObject only because you want them cleaned up when the model gets deleted? If so, then you might just call qDeleteAll() on your columns_ object in the model destructor. And you don't need the Q_OBJECT macro even if you want to keep the QObject legacy. As long as you don't need the meta object for the class (like when declaring new signals or slots), Q_OBJECT is not required.

[Max Yaffe]

Do you need to derive those columns from QObject only because you want them cleaned up when the model gets deleted?

Yes, I wanted to use the cleanup mechanism. I think I read that one can explicitly delete new'ed object, but, let's face it, I'm just lazy. Actually, the cleanup is a great feature of Qt. I also hope to be able to send signals to the columns to force things like change column format, etc.

Thanks for your help.

Max

[wysota]

I think you should manipulate columns this way. The model should be responsible for that and it doesn't need signals and slots. So in general I think you shouldn't derive the columns from QObject. It just doesn't seem to have any advantages and is causing you problems.