Change the thickness of HLine/VLine in Qt Designer - qt

Question

When I am trying to develop a simple UI, to make a visible separation between widgets I decided to use lines. I could use them, but when I try to change the thickness of them it didn't work. And also the lines drawn are incomplete. I changed the lineWidth property to change the thickness. This is the demonstration of how I did it.
Has someone got any experience about this? Can someone show me what I am doing wrong, and how to do it properly?

Answer 1

[NB: the solution given below assumes the default Fusion widget-style is being used. Some other custom styles may impose their own settings, which could very likely produce different results]
There are two separate issues here:
Firstly, to get the desired thickness, you must adjust the following properties of the line:
set the frameShadow to Sunken or Raised
set the lineWidth to zero (this is needed so as to get the exact desired thickness, since it would otherwise increase the total value)
set the midLineWidth to the desired thickness (e.g. 10)
set the minimumHeight (or minimumWidth, for vertical lines) to the same value as above
[optional] set the Mid role in the palette to an appropriate colour
Secondly, to join horizontal and vertical lines so they form a T-junction, you must set the vertcal and/or horizontal spacing to zero for the layouts containing the relevant lines, and then set the stylesheet margins of the neighbouring widgets to restore the spacing wherever needed. To illustrate this, I have added below a simple Qt Designer example. This sets the vertical spacing of the main grid-layout to zero, and also sets the margin-bottom of the top widget, and the margin-top of the two bottom widgets to the default spacing of the layout:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>Form</class>
<widget class="QWidget" name="Form">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>300</height>
</rect>
</property>
<property name="windowTitle">
<string>Form</string>
</property>
<layout class="QGridLayout" name="gridLayout">
<property name="verticalSpacing">
<number>0</number>
</property>
<item row="2" column="1">
<widget class="Line" name="line_2">
<property name="minimumSize">
<size>
<width>10</width>
<height>0</height>
</size>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="midLineWidth">
<number>10</number>
</property>
<property name="orientation">
<enum>Qt::Vertical</enum>
</property>
</widget>
</item>
<item row="1" column="0" colspan="3">
<widget class="Line" name="line">
<property name="minimumSize">
<size>
<width>0</width>
<height>10</height>
</size>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="midLineWidth">
<number>10</number>
</property>
<property name="orientation">
<enum>Qt::Horizontal</enum>
</property>
</widget>
</item>
<item row="2" column="0">
<widget class="QLabel" name="label_2">
<property name="styleSheet">
<string notr="true">background: white; margin-top: 6px</string>
</property>
<property name="frameShape">
<enum>QFrame::StyledPanel</enum>
</property>
</widget>
</item>
<item row="2" column="2">
<widget class="QLabel" name="label_3">
<property name="styleSheet">
<string notr="true">background: white; margin-top: 6px</string>
</property>
<property name="frameShape">
<enum>QFrame::StyledPanel</enum>
</property>
</widget>
</item>
<item row="0" column="0" colspan="3">
<widget class="QLabel" name="label">
<property name="styleSheet">
<string notr="true">background: white; margin-bottom: 6px</string>
</property>
<property name="frameShape">
<enum>QFrame::StyledPanel</enum>
</property>
</widget>
</item>
</layout>
</widget>
<resources/>
<connections/>
</ui>