Are Widgets like LineEdit affected by scope ?

mrmorph

I'm still learning. I'm writing a plugin for Daz Studio.

I found when the form initially loads in my main function that something like :

QLineEdit *leDimWidth = new QLineEdit();
leDimWidth->setText("300");

Will work, but when I use set text in a separate function I get an 'ACCESS_VIOLATION' crash.

leDimWidth is set up in my header like this :

private:
	QLineEdit		*leDimWidth;

The function calling it is in a public slot.

Not quite sure what I might be doing wrong.

Anyone have any ideas please ?

bsomervi

You may be calling QLineEdit::setText() before the widget is constructed or after it has been destroyed.

mrmorph

@bsomervi Nope I don't think so - the application is fully loaded and the layout displayed on screen.

To test it I set the text when I press a button on the layout.

Then it goes to a separate function to set the text, then crashes.

Can you give me one rep so I don't keep getting this 500 second time delay please ? I'm not a spammer :O

kshegunov

@mrmorph
Looks correct, do you mind sharing a bit more of the code?

mrmorph

Here's the code...

main cpp :

..... SNIP....

QLineEdit *leDimWidth = new QLineEdit("11");
QPushButton *button1 = new QPushButton(tr("Button 1"));
	
.....SNIP.....

// * THIS WORKS WHEN SETTING UP THE FORM *
leDimWidth->setText("300");

// Signals and Slots
connect(button1, SIGNAL(pressed()), this, SLOT(doThis("Hmmm")));

..... SNIP....

void Stacker::doThis(QString say) {
	// * THIS DOES NOT WORK - CAUSES CRASH *
	leDimWidth->setText("500");
}

Header File :


...SNIP...

class Stacker : public DzPane {
    Q_OBJECT
public:
    Stacker();
    ~Stacker();

public slots:
    void			doThis(QString say);
private:
	QLineEdit		*leDimWidth;

};

#endif // STACKER_H

mrjj

@mrmorph said:

 QLineEdit *leDimWidth = new QLineEdit();

and you also have one in

private:
    QLineEdit       *leDimWidth;

so should the line
QLineEdit *leDimWidth = new QLineEdit();
not be

leDimWidth = new QLineEdit();

as else you new a local one and the one in "private" is just a dangling pointer?

kshegunov

@mrjj
Good eye! I think you found it. :)

mrmorph

@mrjj Brilliant, thanks a lot, that was it :)

I'd spent ages on this so many thanks.

Great support here.

If you don't mind I will remove most of my code as it's a commercial product.

mrjj

@mrmorph
well I must have confess to have done it myself,
pasting from .h :)
Yeah better remove code then, so u wont get in trouble.

Just a note.
We do not have to new Widgets. Most are quite happy as non pointers.

private:
    QLineEdit    leDimWidth;

mrmorph

@mrjj Well you are good at this, you've saved me again :)

I snipped up my code, but hopefully left enough to show where I went wrong for others.

Thanks again.

Rog.

SGaist

Hi,

Just a quick note, if your widget on stack (i.e. leDimWidth) gets a parent, you'll have a double delete problem since it will get destroyed when the parent is and again when your Stacker object gets destroyed.