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  1. Qt
  2. QTBUG-62818

QPlainTextEdit::setPlainText goes to infinite loop

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Details

    • 3841a7dd49667ceabdcbc416fa1e149bed7ed86e

    Description

      Following code causes the application to go busy loop 

      #include <QApplication>
#include <QPlainTextEdit>

int main(int argc,char*args[])
{
    QApplication app(argc,args);
    QPlainTextEdit *comment = new QPlainTextEdit();
    comment->setPlainText("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\nX\nX\nX");
    auto font = QFontDatabase::systemFont(QFontDatabase::FixedFont);
    comment->setFont(font);
    comment->setWordWrapMode(QTextOption::NoWrap);
    comment->setFixedSize(300,72);
    comment->show();

    return app.exec();
}

       Looks like the same sequence of event is posted again and again on the event loop: 

      QScrollBar - UpdateLater 
QWidget - UpdateLater 
QWidget - MetaCall 
QWidget - ZOrderChange 
QScrollBar - Show 
QWidget - Show 
QWidget - ShowToParent 
QWidget - Hide 
QScrollBar - Hide 
QWidget - HideToParent 
QWidget - Resize 
QWidget - MetaCall 
QWidget - ZOrderChange 
QWidget - Hide 
QScrollBar - Hide 
QWidget - HideToParent 
QScrollBar - Show 
QWidget - Show 
QWidget - ShowToParent 
QWidget - Resize

       
      It looks like the QScrollBars are alternatively hiden and shown. As the event loop is 100% busy, the app is unresponsive.

      This happens if there is exactly three \nX at the end of the text line and the font is FixedFont. 

      Attachments

        1. qtbug62818.zip
          2 kB
        2. QTBUG-62818.zip
          1 kB
        3. qtdiag.txt
          6 kB

        Issue Links

          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-22682 QPlainTextEdit may get stuck trying to adjust scroll bars

          • Not Evaluated - Not yet evaluated/prioritized
          • Closed
          relates to

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-45470 Horizontal scroll bar is not shown in QListView with horizontalScrollBarPolicy and verticalScrollBarPolicy == Qt::ScrollBarAsNeeded

          • P1: Critical - Urgent and Important, will STOP the release if matched with set FixVersion field. This includes regressions from the last version that are not edge cases; Data loss; Build issues; All but the most unlikely crashes/lockups/hanging; Serious usability issues and embarrassing bugs & Bugs critical to a deliverable. This is the highest possible priority for requirements.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-56280 Resizing widget that has QScrollArea with FixedSize layout, causes infinite resize loop due to scrollbars

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-20677 QPrintPreviewWidget hangs

          • P3: Somewhat important - Should be fixed, but doesn't affect the release in any way.
          • Open

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-79906 QTableWidget very high CPU usage when both horizontal and vertical scroll bars shown

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed
          For Gerrit Dashboard: QTBUG-62818
          # Subject Branch Project Status CR V
          214246,4 Prevent infinite relayout when adding scrollbars 5.9 qt/qtbase Status: MERGED +2 0

          Activity

            People

              esabraha Eskil Abrahamsen Blomfeldt
              misalmel Mika Salmela
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              Dates

                Created:
                Updated:
                Resolved:

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