General questions about Model in Qt (docs)

Xilit

I have another bunch of questions. I don't want to start new topic of newbiesh questions so I decided to continue write here.

DOCS:
"Model indexes contain a pointer to the model that created them, and this prevents confusion when working with more than one model".

QAbstractItemModel *model = index.model();

What does .model() means? It must be a member of QAbstractItemModel class but I can't find such memeber in QAbstractItemModel class. Maybe it should be

QAbstractItemModel *model = model.index();

But there is no member index() with no parameters. Also I can't see Model indexes in this example.

Another question.

I always thought that in C++ pure virtual function is obligatory for implementation in child classes. To illustrate that I've created class A with

virtual void myFunction() = 0;

and class B : public A (class B inherits class A). So class A is abstract (you can't create object of such class). Class B is not abstract so I can create object of class B... BUT! Only if I implement virtual function

virtual void myFunction() = 0;

in class B first. Maybe not implement, but just write like that:

void myFunction() override {};

Even without implementation. Only after that I can create object of class B. So implementation of virtual function is obligatory for child classes.

But when I made subclass from QAbstractItemModel with 5 virtual functions ( index(), parent(), rowCount(), columnCount(), and data() ) my project was build even when I commented index(), rowCount(), columnCount() which are virtual. Why if I must implement all virtual functions?

If I press F2 to name of class (for example QStringListModel) I go to header file. But where is cpp-files to see the impementation of it?
Also I'd like to find out what is Qt-class is? I mean Qt::green or Qt::TextFormat? When you type Qt:: you have huge list of autocomplite. Is this superglobal class?

JonB

@Xilit
model() is not a member of QAbstractItemModel, it is an instance of it.. QModelIndex::model() (which is a member of the QModelIndex class) returns the model the index belongs to. It should not be what you said it should be :) With few/rare exceptions, you can rely on the Qt doc pages being correct!

Yes to everything you said about pure virtual (but not just virtual without pure, I think you know that.) So far as I can see they do need implementing in a sub-class, so if you truly derived from QAbstractItemModel you would need to implement. There are queries on the web showing others receiving compiler/linker errors when they fail to do so. I think you'd have to show your code. Thinking aloud, did you instantiate your sub-class? Without that I think it would remain pure virtual itself. As per QAbstractModel class, it does not prevent compiling/linking, but you can't instantiate from it.

Xilit

@JonB

Thank you!

Thinking aloud, did you instantiate your sub-class? Without that I think it would remain pure virtual itself.

I know that was very silly but I didn't create any object of this class.:( When I created it I've got error that I need implement some methods. I didn’t think that I would wait for this error so much.:D

Maybe someone can help me with 3-4 questions? Thank you!

sierdzio

@Xilit said in General questions about Model in Qt (docs):

If I press F2 to name of class (for example QStringListModel) I go to header file. But where is cpp-files to see the impementation of it?

If you checked "Sources" during installation of Qt (in Qt installer) you should be able to go to the .cpp file after pressing F4.

But if you don't have Qt sources, then there is actually no .cpp file so Qt Creator cannot show it.

You can always look the file up, for example in Woboq code browser or by downloading Qt source code manually.

Also I'd like to find out what is Qt-class is? I mean Qt::green or Qt::TextFormat? When you type Qt:: you have huge list of autocomplite. Is this superglobal class?

It's a namespace. See the docs.

Xilit

@sierdzio

Thank you!

That's strange. I've checked "Sources" during installation of Qt but after pressing F4 nothing happend. For exmple I created in my project QAbstractItemModel *model;, put cursor on QAbstractItemModel and press F2 --> go to header (qabstractitemmodel.h). And after pressing F4 nothing happened. Did I made something wrong?

"It's a namespace. See the docs."

Got it. Thank you!

sierdzio

@Xilit said in General questions about Model in Qt (docs):

@sierdzio

Thank you!

That's strange. I've checked "Sources" during installation of Qt but after pressing F4 nothing happend. For exmple I created in my project QAbstractItemModel *model;, put cursor on QAbstractItemModel and press F2 --> go to header (qabstractitemmodel.h). And after pressing F4 nothing happened. Did I made something wrong?

Perhaps it does not work nowadays. Last time I tried this was a long time ago.

"It's a namespace. See the docs."

Got it. Thank you!

Xilit

@sierdzio

Found it in Woboq code browser. According it this file should be in qtbase/src/corelib/itemmodels/qabstractitemmodel.cpp. Thank you for this site.)

I just want to see how rowCount or colomnCount were implemented.

Is this link correct?

J.Hilk

@Xilit said in General questions about Model in Qt (docs):

That's strange. I've checked "Sources" during installation of Qt but after pressing F4 nothing happend. For exmple I created in my projectQAbstractItemModel *model;, put cursor on QAbstractItemModel and press F2 --> go to header (qabstractitemmodel.h). And after pressing F4 nothing happened. Did I made something wrong?

I'm pretty sure, you have to add the path manually in the settings of QtCreator.
Settings -> Debugger -> General -> Add QtSources

Xilit

@J-Hilk

Thank you!

If I correctly inderstand you meant this?

J.Hilk

@Xilit More or less, on the right side you can click on Add Qt sources that opens a QFileDialog, where you select the QtSource folder you downloaded.
After accepting, QtC should set up everything on its own!

Xilit

@J-Hilk

Still don't work.( But as I've mentioned above I've already found in Woboq code browser. On this link).

Interesting. I download Sources to make MySQL work, but it doesn't. Maybe that's why? Because Sqlite does. But I'm not sure what does Target path means.

jsulm

@Xilit Did you use "Add Qt sources..." button to add Qt sources?

Xilit

@jsulm

Yes, I did. I think I pressed just Add instead of Add Qt sources. Now it's look like:

But when I press F4 in header file (qabstractitemmodel.h) nothing happens. It still don't want to show me cpp file.