Beginners: signal slot help

SherifOmran

hello guys,

I ve a class and in this class I create a new QWidget to show an image. I want to get the signal when this QWidget is closed, or even the possibility to know if it is open or closed.

here is how I build it from inside my class. the connect has a mistake.

myclass.h
@
private:
QWidget *blub;
@

@myclass.cpp

        QWidget *blub = new QWidget();
        blub->resize(250,230);
        blub->setWindowFlags((windowFlags() | Qt::CustomizeWindowHint) & ~Qt::WindowMaximizeButtonHint); //no resize
        connect(blub,SIGNAL(destroyed(blub)),this,SLOT(handwindowcloseevent()));

@

ChrisW67

The connect() should read:

@connect(blub,SIGNAL(destroyed()),this,SLOT(handwindowcloseevent()));
@

However, there is a difference between closed, as in hidden, and destroyed where the object is being torn down (after a delete or going out of scope). QWidget::visible() will tell you if the widget is visible. You can use the QWidget::closeEvent() (in the blub object) to do pre-close processing if that suits your purposes.

pwnstar23

Use a QPointer instead of a naked pointer. This will save you later on. The QPointer will null itself when the Widget is freed.

Then call
setAttribute( Qt::WA_DeleteOnClose, true );
on your widget it will delete itself when closed.
And because you use a QPointer the pointer will be null as well.

SherifOmran

What is QPointer can you give me an example?

I tried the connect as stated above but it did not work, unfortunately, do i miss something else? Should I create it as a class?

pwnstar23

@
QPointer<QWidget> blub;
blub = new QWidget():
@

A QPointer is just Qt's class wrapper for Qt dynamic memory.

SherifOmran

is it possible say to get keyboard events from the main widget irregardless which (it or blub) has focus.

can i put in the main widget @this->grabkeyboard();@ ?

rapunzel

hello m usind qt designer for first time.. i need to create a calculator using three line edits and two pushbutoons for addition and equality.
cn anyone help me with the code using signals and slots??

SherifOmran

see this video to learn more about signal and slots
https://www.youtube.com/watch?v=GxlB34Cn0zw

rapunzel

hello hav to design a calculator in which if a value becomes more than 10 color of button changes to red otherwise green..
plzzz help me with the code

Sam

You can connect the textChanged() signal of the lineEdit to a slot where you can check the count using
lineEdit->text().length() you can also set the maxlengh like lineEdit->setMaxLength().