Application hangs after using up/down arrows in scrollbar of scrollarea widget

Vidya H

I am running a Qt5.15 based application on a embedded Linux platform target. I have a QScrollArea widget to display particular information. There is a scrollbar with up and down arrows.

When I use the scrollbar, the scrolling is smooth. However, when I press and hold the up/down arrow, it starts to scroll and within few seconds, the UI hangs.

Please suggest how to fix this. Let me know if further details are required.

SGaist

Hi,

Did you set any configuration on the scroll area's QScrollBars ?
How big is it ?

Vidya H

@SGaist , below is a snippet of the scroll area properties. Label "lblSysInfoSystemName" is available in the below snippet for reference. The area is huge with multiple such labels.

Please note that this is a multi-threaded application.

<widget class="QScrollArea" name="scrollArea">
    <property name="geometry">
     <rect>
      <x>14</x>
      <y>198</y>
      <width>996</width>
      <height>290</height>
     </rect>
    </property>
    <property name="styleSheet">
     <string notr="true">QScrollArea QWidget
{   
    background-color:rgba(0,0,0,0);
}


/******************************* ScrollBar Vertical ***********************************/

QScrollBar:vertical 
{
  border-color:rgb(76,76,76);
  border-radius: 8px;
  background-color:rgb(76,76,76);
  width:65px;
  margin: 0px 0px 0px 5px;
}

QScrollBar::handle:vertical 
{
  background-color: rgb(100, 191, 187);
  min-height: 50px;
  border-radius: 8px;
  margin: 60px 5px 60px 5px;
}

QScrollBar::handle:vertical:disabled 
{
  background-color:rgb(76,76,76);
  min-height: 50px;
  border-radius: 8px;
  margin: 60px 5px 60px 5px;
}

 QScrollBar::add-line:vertical
{
   background-color: rgb(76,76,76);
   height: 56px;
   subcontrol-position: bottom;
   subcontrol-origin: margin;
   margin: 0px 0px 0px 5px; 
   border-bottom-right-radius:8px;
	border-bottom-left-radius:8px;
}

QScrollBar::add-line:vertical::pressed
{
   background-color: rgb(100, 191, 187);
   height: 56px;
   subcontrol-position: bottom;
   subcontrol-origin: margin;
   margin: 0px 0px 0px 5px; 
 border-bottom-right-radius:8px;
	border-bottom-left-radius:8px;
}

QScrollBar::sub-line:vertical 
{
   background-color:rgb(76,76,76);
   height: 56px;
   subcontrol-position: top;
   subcontrol-origin: margin;
    margin: 0px 0px 0px 5px;
	border-top-right-radius:8px;
	border-top-left-radius:8px;
}

QScrollBar::sub-line:vertical::pressed
{
   background-color: rgb(100, 191, 187);
  height: 56px;
   subcontrol-position: top;
   subcontrol-origin: margin;
    margin: 0px 0px 0px 3px;
	border-top-right-radius:8px;
	border-top-left-radius:8px;
}

QScrollBar::add-page:vertical, QScrollBar::sub-page:vertical 
{
   background-color: none;
}

QScrollBar::up-arrow:vertical
{
	image:url(:/new/Images/resources/UIImages/UpArrowWhite.png);
	margin-top:2px;
}

QScrollBar::up-arrow:vertical::pressed
{
	image:url(:/new/Images/resources/UIImages/UpArrowWhite.png);
	margin-top:2px;
}

QScrollBar::up-arrow:vertical:disabled
{
  image: none;
}

QScrollBar::down-arrow:vertical
{
 	image:url(:/new/Images/resources/UIImages/DownArrowWhite.png);
	margin-bottom:2px;
}

QScrollBar::down-arrow:vertical::pressed
{
  image:url(:/new/Images/resources/UIImages/DownArrowWhite.png);
	margin-bottom:2px;
}
QScrollBar::down-arrow:vertical:disabled
{
  image: none;
}
</string>
    </property>
    <property name="verticalScrollBarPolicy">
     <enum>Qt::ScrollBarAsNeeded</enum>
    </property>
    <property name="sizeAdjustPolicy">
     <enum>QAbstractScrollArea::AdjustIgnored</enum>
    </property>
    <property name="widgetResizable">
     <bool>true</bool>
    </property>
    <widget class="QWidget" name="scrollAreaWidgetContents">
     <property name="geometry">
      <rect>
       <x>0</x>
       <y>0</y>
       <width>980</width>
       <height>1955</height>
      </rect>
     </property>
     <property name="minimumSize">
      <size>
       <width>0</width>
       <height>1955</height>
      </size>
     </property>
     <widget class="QLabel" name="lblSysInfoSystemName">
      <property name="geometry">
       <rect>
        <x>0</x>
        <y>0</y>
        <width>552</width>
        <height>55</height>
       </rect>
      </property>
      <property name="font">
       <font>
        <family>Helvetica LT</family>
        <pointsize>17</pointsize>
       </font>
      </property>
      <property name="styleSheet">
       <string notr="true">/**************** Label *************************/

SGaist

How huge is this QScrollArea ?

Vidya H

This is how the screen looks like. I have hidden sensitive information.

SGaist

Can you provide a minimal compilable example that reproduces this behavior ?

Vidya H

I tested the example code in Qt and it works fine on the target board. I am using linuxfb platform. Could this be something to do with the environment variables?

Vidya H

@SGaist , could you please help on this issue? Is this due to Qt framework or my application or root file system or environment variables setting? I want to narrow down the issue.

OZVID Technologies

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ElizabethTurner

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SGaist

@Vidya-H If the Qt example is working properly on the target then it means that something is wrong with your application.

Not knowing more about it, one classical way to find the issue is to remove everything from the application then add gradually things back until it breaks again.

Vidya H

Okay. I added delay of 20 millisecond when scroll bar value changed. I am seeing performance improvement with this. The application hang frequency has reduced drastically. Is this a correct approach? Please suggest.

SGaist

No it's not a correct approach.
You have to find what is currently slowing down your application.
Like I wrote above, the most basic version of it is starting from scratch adding your elements one at a time to determine what is going wrong.
Another option is to instrument your application and analyse it with a tool such as Hotspot.

Vidya H

Thank you for the support. I will use this tool for further analysis.