QWT Plot Curve Dashline not showing

[horizonQt]

Hi everyone,
Im using qwtplot and ı want curve to be dashline.
curve->setPen(Qt::red, 2, Qt::Dashline);

but not working. I can't see dashed when the graph is flowing. I can see it in the changes and when I zoom in.

[SGaist]

Hi,

Please provide a minimal compilable example that shows the situation.