Help with QWidget::show()

mmikeinsantarosa

I need to call a function when a QWidget gets its show() method gets called and I have looked at examples for Mainwindow but I don't understand how this works.
The widget that needs to implement show() is called ChartProperties. For declaring it in the header,
void MainWindow::showEvent(QShowEvent *ev);
doesn't work because this isn't a mainwindow and
void ChartProperties::showEvent(QShowEvent *ev)
complains about an extra member showevent.

Any suggestions would be much appreciated.

I'm clueless here and thanks for any response.

SGaist

Hi,

@mmikeinsantarosa said in Help with QWidget::show():

I have irtual void showEvent(QShowEvent *event) override;

This is just a declaration, you still have to implement the function itself.

Christian Ehrlicher

@mmikeinsantarosa said in Help with QWidget::show():

void ChartProperties::showEvent(QShowEvent *ev)
complains about an extra member showevent.

What exact error message do you get?

mmikeinsantarosa

@Christian-Ehrlicher said in Help with QWidget::show():

void ChartProperties::showEvent(QShowEvent *ev)

I get "extra qualification on member 'showEvent'"

mmikeinsantarosa

And the widget is actually a "QDialog".

Christian Ehrlicher

And please show how you defined and declared this function.

mmikeinsantarosa

Realizing that the class is actually a QDialog so I just changed the declaration to
virtual void showEvent(QShowEvent *event) override;
and it doesn't complain now.

So now, how do I hook it up to execute another function?
Right clicking on it and selecting refactor doesn't provide a way to create a function in my source. Do I need to create a slot to connect it to?

Christian Ehrlicher

@mmikeinsantarosa said in Help with QWidget::show():

So now, how do I hook it up to execute another function?

I don't understand this question. Simply create a function in your class and call it from within your other function.

mmikeinsantarosa

Sorry, I'm feeling pretty dumb here.

Another class executes the ChartProperties->Show() method and when the dialog is rendered, I want to trap the ChartProperties show() event.
I have irtual void showEvent(QShowEvent *event) override;
in my ChartProperties header but I don't understand how to receive the showEvent..

Christian Ehrlicher

As explained in the documentation this function is called when the widget is shown, you must not call it by yourself.

SGaist

Hi,

@mmikeinsantarosa said in Help with QWidget::show():

I have irtual void showEvent(QShowEvent *event) override;

This is just a declaration, you still have to implement the function itself.

mmikeinsantarosa

Do I create a slot then connect this event to my slot?

Christian Ehrlicher

@mmikeinsantarosa said in Help with QWidget::show():

Do I create a slot then connect this event to my slot?

What slot? showEvent() is a class function, not a slot. Please learn C++ basics first.

mpergand

@mmikeinsantarosa

Your question seems pretty close this this one

As an alternative, you can simply do:

MyDialog::show()
{
  myFunction();
  QDialog::show();
}

Using showEvent is dangerous cause it can be called multi times !

mmikeinsantarosa

The method name is "showEvent" which leads me to think it's a signal. It's also listed in the signals list in the documentation for QDialog so I thought it might actually be a signal.

thanks for clearing this up SGaist.

SGaist

@mmikeinsantarosa said in Help with QWidget::show():

It's also listed in the signals list in the documentation for QDialog

That's wrong, neither in the Qt 5 nor in the Qt 6 documentation.

It is listed under Reimplemented Protected Functions.

Beside that, signals name do not finish in "event". They usually have a name in relation to some action like rejected in QDialog.

mmikeinsantarosa

I stand corrected. entering QDialog in the Qt help and selecting signals reveals signals at the top, with 3 items under it then Reimplemented Protected Functions where the showEvent function is listed.

JonB

@mmikeinsantarosa
Indeed, that is how Qt documentation lays out its methods.

To reiterate something @Christian-Ehrlicher said. In Qt nomenclature:

Methods ending in Event (showEvent(), mouseMoveEvent()) are not signals. Instead they are protected virtual methods. You must sub-class and override if you want to access them.
Signals tend to be named as the past tense of something that has happened (clicked(), customContextMenuRequested()). You cannot override them. You can connect() to them, without needing to sub-class.
And slots are just named as an action to be performed (show(), setDiabled()).