General questions about Model in Qt (docs)
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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
QAbstractItemModelclass but I can't find such memeber inQAbstractItemModelclass. Maybe it should beQAbstractItemModel *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
QAbstractItemModelwith 5 virtual functions (index(),parent(),rowCount(),columnCount(), anddata()) my project was build even when I commentedindex(),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::greenorQt::TextFormat? When you typeQt::you have huge list of autocomplite. Is this superglobal class?
@Xilit
model()is not a member ofQAbstractItemModel, it is an instance of it..QModelIndex::model()(which is a member of theQModelIndexclass) 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
QAbstractItemModelyou 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 perQAbstractModelclass, it does not prevent compiling/linking, but you can't instantiate from it. - DOCS:
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@Xilit
model()is not a member ofQAbstractItemModel, it is an instance of it..QModelIndex::model()(which is a member of theQModelIndexclass) 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
QAbstractItemModelyou 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 perQAbstractModelclass, it does not prevent compiling/linking, but you can't instantiate from it.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!
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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
QAbstractItemModelclass but I can't find such memeber inQAbstractItemModelclass. Maybe it should beQAbstractItemModel *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
QAbstractItemModelwith 5 virtual functions (index(),parent(),rowCount(),columnCount(), anddata()) my project was build even when I commentedindex(),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::greenorQt::TextFormat? When you typeQt::you have huge list of autocomplite. Is this superglobal class?
@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.
- DOCS:
-
@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.
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 onQAbstractItemModeland 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!
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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 onQAbstractItemModeland 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!
@Xilit said in General questions about Model in Qt (docs):
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 onQAbstractItemModeland 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 said in General questions about Model in Qt (docs):
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 onQAbstractItemModeland 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!
-
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 onQAbstractItemModeland 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!
@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 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 More or less, on the right side you can click on
Add Qt sourcesthat opens a QFileDialog, where you select the QtSource folder you downloaded.
After accepting, QtC should set up everything on its own!@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
Sourcesto make MySQL work, but it doesn't. Maybe that's why? Because Sqlite does. But I'm not sure what doesTarget pathmeans. -
@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
Sourcesto make MySQL work, but it doesn't. Maybe that's why? Because Sqlite does. But I'm not sure what doesTarget pathmeans.
