Why VerticalHeaderItem cause crit.error

Engelard

When i add any action to my VertHItem - in runtime it cause crit error and the program stop working. I've included QHeaderView, certain Item indeed exist, but i simply can't set text for it:

if(tabWidGuide.verticalHeaderItem(0)->text()=="1") tabWidGuide.verticalHeaderItem(0)->setBackground(Qt::red);

That code assures that item at '0' exist and it's label is 1, which is true, it 1 by default in my app.

P.S. here is it in documentation

mrjj

Hi
You should check its not NULL
try
qDebug() << "item = " << tabWidGuide.verticalHeaderItem(0);

jsulm

@Engelard said in Why VerticalHeaderItem cause crit.error:

if(tabWidGuide.verticalHeaderItem(0)->text()=="1") tabWidGuide.verticalHeaderItem(0)->setBackground(Qt::red);

To add to @mrjj : you should ALWAYS check pointers before dereferencing them!

if(tabWidGuide.verticalHeaderItem(0) && tabWidGuide.verticalHeaderItem(0)->text()=="1") tabWidGuide.verticalHeaderItem(0)->setBackground(Qt::red);

aha_1980

@Engelard

And that's exactly the difference between pointers and references you have to understand.

Pointers have to be checked against nullptr before de-referencing, references can always be used.

JonB

@jsulm , @aha_1980
I agree with your advice. However, I took the OP at his word when his question states

[I am] certain Item indeed exist

I shall be interested to see whether he comes back and says that pointer was NULL after all, maybe I'm too trusting...!

Engelard

Tnx for all advices for checking item, now it shows that header does'nt exist. BUT. Why it exist in the app, and it returning like it does'nt?

aha_1980

@Engelard

Why it exist in the app, and it returning like it does'nt?

How do you set it?
Do you set it before your read it back?

Engelard

@aha_1980 i didn't set anything, i assume that it set by default, so why would i set it..

aha_1980

@Engelard said in Why VerticalHeaderItem cause crit.error:

i assume that it set by default,

It isn't.