Access and inheritance
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Hi
If you add contextMenuEvent to MainWindow, then you need
to right click the actual MainWindow, to trigger it.
It wont be triggered by right clicking on the spreadSheet widget.
So not sure having them in MainWindow is what you want ?- One question as well, what will we achieve by re-implementing that virtual protected method please?
Well it allows us to override a default contextMenuEvent so for any widget that can actually show a menu already( like QlineEdit)
it allows to to alter what should be shown ( a new menu )
Or it allows us to add a menu to a QWidget that dont already have such menu.BUT
Often the signal is used instead (of the Event ) as that requires no subclass.
https://doc.qt.io/qt-5/qwidget.html#customContextMenuRequested
That you can just connect to and do get the same effect without subclassing.However, WHAT widget do you want to add contextMenu to ?
The spreadsheet? -
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Hi I would use the SIGNAL then.
I assume it has not right click menu already?
To use it, you enable it with
ui->spreadsheet->setContextMenuPolicy(Qt::CustomContextMenu);
(ui->spreadsheet might not be actual name ;)then connect signal to a slot where you build and exec() the menu.
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I assume it has not right click menu already?
It has. The author said: "A more sophisticated way of providing context menus is to reimplement the QWidget::contextMenuEvent() function,
create a QMenu widget, populate it with the desired actions, and call exec() on it.", so I was motivated to re-implement that method to probably have a nicer or more advanced context menu for the cells!
By the way, I like to use pure code only (no design mode). :) -
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@mrjj Hi,
Yes. The book also shows the code for that.
I know I can add more options to that, for instance, to have five buttons in the context menu rather than that three ones. But by the sentence the author said, I though there should be another way to have a more advanced context menu by re-implementing the virtual protected method when mentioned earlier.By the way, don't you have that book?
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@tomy
Hi
Well the menu already have both shortcut and icon so not sure what else could be added.
There is no "more advanced" menu possible by overwriting contextMenuEvent as
you can just 100% the same just altering
void MainWindow::createActions()
to show what you want.yes, i have it as PDF. did read most of it way back.
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Thank you very much. I was too much stuck in a QML program's problem, sorry for the delay.
If you run the program, even by the latest version of Qt Creator and on a sophisticated and fancy operating system like Windows 10, you see the program still looks old, as though we are in 2000 using it.
Is it because of the code? If so, what parts can be updated, please? -
@tomy
Hi
Nope its just how the QWidgets look.
If you change the icons to flat style,
it will look more "modern"You could use something like
https://github.com/laserpants/qt-material-widgets
if you want to go all in for "modern" look. -
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@mrjj said in Access and inheritance:
The truth is, if a base class do not do anything in its constructor, nothing bad will happen not calling it.
Just for completeness:
If the base class has a default constructor, and it's not called explicitly in the derived class' constructor the compiler is going to generate code to call it implicitly. Omitting it in the initializer list means nothing here, asQMainWindow()is going to be called either way. If the base class does not have a default constructor, and there's no call to the parent's constructor then this is going to generate a compile error, as the compiler has no idea what to do. -
@kshegunov
Hi,If the base class has a default constructor, and it's not called explicitly in the derived class' constructor the compiler is going to generate code to call it implicitly. Omitting it in the initializer list means nothing here, as
QMainWindow()is going to be called either way.Is it true for the Qt Creator compiler too? (I think so)
If the base class does not have a default constructor, and there's no call to the parent's constructor then this is going to generate a compile error, as the compiler has no idea what to do.
Can we conclude this way that, when the base class doesn't have a constructor, in either way, whether the subclass calls the parent's constructor (!) or it doesn't, we will get an error?
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@tomy said in Access and inheritance:
Is it true for the Qt Creator compiler too? (I think so)
Qt Creator is not a compiler, it uses some compiler (whatever you've configured), but yes, it's true for all compiler, as this is standard (and required) behaviour for C++.
Can we conclude this way that, when the base class doesn't have a constructor, in either way, whether the subclass calls the parent's constructor (!) or it doesn't, we will get an error?
No. Not defining a class constructor means the compiler generates a default one for you (unless specifically told otherwise). If you haven't defined a constructor in the base class, then the derived class is going to implicitly call the automatically generated one.
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So we will never have to call the base class's constructor from the subclass, because if there is an explicit constructor for the base class, the compiler calls (implicitly) for us (with the absence of an explicit call from us), and if there is no constructor for the base class, the compiler creates a default one and implicitly calls that in the subclass. Hence, we had better never involve ourselves with calling a base class's constructor directly (from the subclass)! :) :)
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@tomy
Hi
The automatic version is only for a default constructor.
As soon as base class constructor takes parameters, it must be called from subclass as compiler cannot
know how to obtain the parameters to give to base class.
However the compiler will tell you that. -
What @mrjj said, plus the moment you define a constructor, the compiler stops generating for you. Thus if you define a constructor with parameters, the compiler will not generate a default constructor for you. Beautiful system, right? :)
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If you change the icons to flat style, it will look more "modern"
Hi,
The example you posted look very modern and stylish, but too advanced for me now. Thank you.
I like to go step by step. So for the icons, I must download some "flat .png related files" from the Internet and substitute the old ones with these. Right?
