Trouble with custom QSlider

Smeeth

@SGaist Sorry, by "put it on the stack" do you mean use a member variable? Or somehow access the painter object without instantiating it each time?

I went back to QSlider but setting the max-width for the groove doesn't change the width of the handle, it still extends to the wide size policy of the widget.

arsinte_andrei

@Smeeth
I think he is referring to the

auto painter = new QPainter(this);

like that painter get destroyed only with the form
so you should change that ...
and also is getting a new place in memory everytime you touch the slider - careful with the memory management

Smeeth

@arsinte_andrei Got it. So how can I get the painter without calling new QPainter(this)?

SGaist

QPainter painter(this);

arsinte_andrei

@Smeeth here you have two options -

delete

private:
QPainter *painter;

and

painter = new QPainter(this);

and inside the paint event add

void AlarmLimitsSlider::paintEvent(QPaintEvent *ev) {
QPainter painter;
//TODO the painting

options
you have declared the painter as a global variable... so make a global init

so in your constructor add

painter = new QPainter(this);

and delete it from the paint event

Smeeth

@arsinte_andrei Oh I see, for some reason I thought you had to create a new Painter for each time the paint event is triggered. I will try this solution.

SGaist

Based on the documentation of QPainter:

The common use of QPainter is inside a widget's paint event: Construct and customize (e.g. set the pen or the brush) the painter. Then draw. Remember to destroy the QPainter object after drawing. For example:

arsinte_andrei

so as SGaist sugest.. and he is right... at option 2 keep

painter = new QPainter(this);

the first line in the paintEvent and add

delete painter;

as your last line in the paint event...

but anyway I do not understand why will you want option 2 when option 1 is the best???

SGaist

@arsinte_andrei said in Trouble with custom QSlider:

so as SGaist sugest.. and he is right... at option 2 keep
painter = new QPainter(this);
the first line in the paintEvent and add
delete painter;
as your last line in the paint event...

but anyway I do not understand why will you want option 2 when option 1 is the best???

It's not what I suggested, use a stack base painter, there's really no need to allocate if on the heap.

arsinte_andrei

@SGaist you pointed at the option 2.. but if you look at option 1 is exactly what you have said.. this is what I've recommended...

void AlarmLimitsSlider::paintEvent(QPaintEvent *ev) {
QPainter painter;
//TODO the painting

or

void AlarmLimitsSlider::paintEvent(QPaintEvent *ev) {
QPainter painter(this);
//TODO the painting

same thing.. - except the second one has parent

SGaist

It's not the same thing. It's not a parent, it's the paint device that the painter will be active on. If you don't pass it, you will have to call begin and end explicitly. See the constructor documentation.

arsinte_andrei

Hmm.... After years pf doing Qt programming I have to agree that I still have a lot to learn about... I do apologize for the wrong information that I've provided....
Best explanation... God bless SGaist...