[kind of solved] subclassed QAbstractTableModel::setData does not get called

andi456

It seems, as if QAbstractTableModel subclasses do not like nlohmann::json parameters to be passed to their constructor. I've started another project with basically the same subclass and it shows the same error of an undefined reference to vtable. I guess the setData method would not get called, even if i found a way to get it to compile.

Could this be an issue of the nlohmann::json library? Or what could one do to further investigate the issue?

JonB

@andi456 said in subclassed QAbstractTableModel::setData does not get called:

as if QAbstractTableModel subclasses do not like nlohmann::json parameters to be passed to their constructor.

Don't know what you mean. QAbstractTableModel doesn't know anything about JSON. What you do with nlohmann::json parameters is up to you.

andi456

Well, that's why I tried to pass a nlohmann::json argument to the constructor, which results in the obscure "undefined reference to vtable" error for the QAbstractTableModel subclass. After some research on the internet this error can have all kinds of causes. But I do not see any obvious error in my code.

Christian Ehrlicher

What build system do you use? Is the moc file for zaubertablemodel.h generated, compiled and linked?

SGaist

Hi,

Might be a silly question but do you build the class code along with your test ?

andi456

@SGaist No, I've written both a minimal test project and a test. The errors were similar. After running qmake on the minimal testproject, new errors occurred:
:-1: Fehler: moc_ztablemodel.o:(.data.rel.ro._ZTV11ZTableModel[_ZTV11ZTableModel]+0xb0): undefined reference to `ZTableModel::headerData(int, Qt::Orientation, int) const'

And so on for all the reimplemented methods of QAbstractTableModel.

The moc_* files are there obviously but cannot be linked somehow?

SGaist

Missing symbols suggests that you might be:

not building the class sources
not implementing the methods

One thing you can is start from an empty class and the gradually add the methods to see where it breaks

andi456

Don't i have to implement at least

code_text
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const  Q_DECL_OVERRIDE;
int rowCount(const QModelIndex &parent = QModelIndex()) const  Q_DECL_OVERRIDE;
int columnCount(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;```
code_text

? That's what I did in my minimal test class .

Christian Ehrlicher

@andi456 said in subclassed QAbstractTableModel::setData does not get called:

That's what I did in my minimal test class .

But you declared headerData() without providing an implementation.

andi456

@Christian-Ehrlicher The relevant parts of the implementation can be found in my first post in the second code block. I just copied the necessary parts to my minimal test example, created with qtcreator.

Christian Ehrlicher

@andi456 but even there I see no headerData() implementation...

andi456

Here it is:

QVariant ZTableModel::headerData(int section, Qt::Orientation orientation, int role) const
{
QList<QString> headerliste = ZTableModel::get_header(j_zl);
    if (role != Qt::DisplayRole) {
    return QVariant();
}
if (orientation == Qt::Horizontal) {
    for (int i=0; i < headerliste.size(); ++i) {
        QString s = headerliste.at(i);
    if (i == section) {
        return s;
        break;
    }
    }
}

JonB

@andi456
@Christian-Ehrlicher said you had not implemented headerData().
The error messages you pasted includes

undefined reference to ZTableModel::headerData(int, Qt::Orientation, int) const

Do you not think this indicates a problem?

JonB

@andi456 said in subclassed QAbstractTableModel::setData does not get called:

Here it is:

Your post crossed with mine.

Could you please delete all object files etc. and do a clean rebuild from scratch. If you still get an error could you copy & paste that/those.

andi456

I see, got the minimal example to compile. It was a matter of the header declarations that i forgot to comment out.. Thank you.. I'll see what happens after the implementation of setData and flags and report back later.

andi456

After implementing the setData and flags and making use of the convenient debugging capabilities of qtcreator, I can now tell that setData is being called, when i enter something from the keyboard, which seems to be discarded afterwards.

Edit: Wrong impression on first Debug run.

Update: The new value is being put into the json-object, according to the debugging information, dataChanged is being emitted too, but for some reason the change is not being displayed. What might i be missing?

I missed writing back the data into the json list in the setData method.

andi456

First of all, thank you all for your support. The reason, why I wrote "kind of solved" into the headline of the post, is the following. I just loaded the original project into qtcreator in order to debug it. qtcreator seems to have run some scripts and the setData method got actually called without the code having changed at all. Unfortunately, I do not know what was necessary. (I just used vim for writing the program before.)