c++ - Qt paintEvent crashes -

im trying draw simple board on widget.

when i'm trying automatize this, paintevent crashes. think caused loop inside, right? how paint in other way?

void widget::paintevent(qpaintevent *event) { qpixmap mypix( qsize(20,20) ); qpainter painter(this); for(int = 0; < 100; i+5){     painter.drawline(qpointf(i,0),qpointf(i,max)); } this->setpixmap(mypix); } 

your loop incorrect , causes program crash (i'm sure that's not fault here). should written this:

for(int = 0; < 100; i+=5){     p.drawline(qpointf(i,0),qpointf(i,max)); } 

i.e. assignment of increment. way job , finish properly.

on side note, suggest use drawpixmap() instead of setpixmap(). setpixmap() not cause infinite recursion , example next code works properly.

//... this->setpixmap(qpixmap("g:/2/qt.jpg")); qlabel::paintevent(event); 

why? approach infinite recursion never produced (see here):

if call repaint() in function may called paintevent(), may infinite recursion. update() function never causes recursion.

indeed setpixmap() calls update(), not repaint(). prove see source code:

setpixmap source:

void qlabel::setpixmap(const qpixmap &pixmap) {     q_d(qlabel);     //...     d->updatelabel();//what does? } 

updatelabel source:

void qlabelprivate::updatelabel() {     q_q(qlabel);     //...     q->updategeometry();     q->update(q->contentsrect());//not repaint  } 

as said not mistake think better if need qpainter.