Modified Qt ElidedLabel that shrinks to fit content (see https://stackoverflow.com/q/56365244/187359 )

elidedlabel.cpp

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
**   * Redistributions of source code must retain the above copyright
**     notice, this list of conditions and the following disclaimer.
**   * Redistributions in binary form must reproduce the above copyright
**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
**     distribution.
**   * Neither the name of The Qt Company Ltd nor the names of its
**     contributors may be used to endorse or promote products derived
**     from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/


#include "elidedlabel.h"

#include <QPainter>
#include <QTextLayout>
#include <QDebug>

ElidedLabel::ElidedLabel(/*const QString &text, */QWidget *parent)
    : QFrame(parent)
    , elided(false)
//    , content(text)
{
//    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Preferred);
}

void ElidedLabel::setText(const QString &newText)
{
    content = newText;
    update();
    adjustSize(); // Will resize the label
}

void ElidedLabel::paintEvent(QPaintEvent *event)
{
    QFrame::paintEvent(event);

    QPainter painter(this);
    QFontMetrics fontMetrics = painter.fontMetrics();

    bool didElide = false;
    int lineSpacing = fontMetrics.lineSpacing();
    int y = 0;

    QTextLayout textLayout(content, painter.font());
    textLayout.beginLayout();
    forever {
        QTextLine line = textLayout.createLine();

        if (!line.isValid())
            break;

        line.setLineWidth(width());
        int nextLineY = y + lineSpacing;

        if (height() >= nextLineY + lineSpacing) {
            line.draw(&painter, QPoint(0, y));
            y = nextLineY;
        } else {
            QString lastLine = content.mid(line.textStart());
            QString elidedLastLine = fontMetrics.elidedText(lastLine, Qt::ElideRight, width());
            painter.drawText(QPoint(0, y + fontMetrics.ascent()), elidedLastLine);
            line = textLayout.createLine();
            didElide = line.isValid();
            break;
        }
    }
    textLayout.endLayout();

    if (didElide != elided) {
        elided = didElide;
        emit elisionChanged(didElide);
    }
}

QSize ElidedLabel::sizeHint() const
{
    QFontMetrics const fontMetrics(font());
    QRect const r = fontMetrics.boundingRect(
            QRect(QPoint(0, 0), size()),
            Qt::TextWordWrap | Qt::ElideRight,
            content
            );
    return QSize(width(), r.height());
}

void ElidedLabel::resizeEvent(QResizeEvent* event)
{
    QFrame::resizeEvent(event); // Process the event. The label is now resized
    QSize const size = sizeHint();
    if (size.height() < height()) // Shrink the height if needed
        resize(QSize(width(), size.height()));
}

elidedlabel.h

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
**   * Redistributions of source code must retain the above copyright
**     notice, this list of conditions and the following disclaimer.
**   * Redistributions in binary form must reproduce the above copyright
**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
**     distribution.
**   * Neither the name of The Qt Company Ltd nor the names of its
**     contributors may be used to endorse or promote products derived
**     from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/


#ifndef ELIDEDLABEL_H
#define ELIDEDLABEL_H

#include <QtWidgets/QFrame>
#include <QtCore/QRect>
#include <QtGui/QResizeEvent>
#include <QtCore/QString>
#include <QtWidgets/QWidget>

class ElidedLabel : public QFrame
{
    Q_OBJECT
    Q_PROPERTY(QString text READ text WRITE setText)
    Q_PROPERTY(bool isElided READ isElided)

public:
    explicit ElidedLabel(/*const QString &text, */QWidget *parent = nullptr);

    void setText(const QString &text);
    const QString & text() const { return content; }
    bool isElided() const { return elided; }

protected:
    void paintEvent(QPaintEvent *event) override;
    QSize sizeHint() const override;
    void resizeEvent(QResizeEvent* ) override;

signals:
    void elisionChanged(bool elided);

private:
    bool elided;
    QString content;
};

#endif

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

namespace
{
    const auto s_longText = QStringLiteral("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean porttitor lorem felis, id mattis urna vulputate ac. Pellentesque mi nunc, interdum eget urna eget, venenatis elementum tellus. In in tempus nunc. Vivamus porta quis nibh vitae dictum. Etiam sem orci, laoreet non efficitur a, molestie eget ipsum. Praesent vitae velit ante. Ut molestie congue libero, id hendrerit lacus lacinia eu. Sed ornare diam vehicula, tristique ex et, commodo ante. ");
    const auto s_shortText = QStringLiteral("Foo bar baz foo bar baz");
}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->elidedLabelShort->setText(s_shortText);
    ui->elidedLabelLong->setText(s_longText);
}

MainWindow::~MainWindow()
{
    delete ui;
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <property name="maximumSize">
    <size>
     <width>200</width>
     <height>16777215</height>
    </size>
   </property>
   <layout class="QHBoxLayout" name="horizontalLayout">
    <item>
     <layout class="QVBoxLayout" name="verticalLayout">
      <property name="spacing">
       <number>0</number>
      </property>
      <item>
       <widget class="ElidedLabel" name="elidedLabelShort">
        <property name="maximumSize">
         <size>
          <width>16777215</width>
          <height>60</height>
         </size>
        </property>
        <property name="styleSheet">
         <string notr="true">background-color:#ddddff;</string>
        </property>
        <property name="frameShape">
         <enum>QFrame::StyledPanel</enum>
        </property>
        <property name="frameShadow">
         <enum>QFrame::Raised</enum>
        </property>
       </widget>
      </item>
      <item>
       <widget class="QLabel" name="label_2">
        <property name="sizePolicy">
         <sizepolicy hsizetype="Preferred" vsizetype="Expanding">
          <horstretch>0</horstretch>
          <verstretch>0</verstretch>
         </sizepolicy>
        </property>
        <property name="styleSheet">
         <string notr="true">background-color:#ffdddd;</string>
        </property>
        <property name="text">
         <string>TextLabel</string>
        </property>
       </widget>
      </item>
     </layout>
    </item>
    <item>
     <layout class="QVBoxLayout" name="verticalLayout_3">
      <property name="spacing">
       <number>0</number>
      </property>
      <item>
       <widget class="ElidedLabel" name="elidedLabelLong">
        <property name="maximumSize">
         <size>
          <width>16777215</width>
          <height>60</height>
         </size>
        </property>
        <property name="styleSheet">
         <string notr="true">background-color:#ddddff;</string>
        </property>
        <property name="frameShape">
         <enum>QFrame::StyledPanel</enum>
        </property>
        <property name="frameShadow">
         <enum>QFrame::Raised</enum>
        </property>
       </widget>
      </item>
      <item>
       <widget class="QLabel" name="label">
        <property name="sizePolicy">
         <sizepolicy hsizetype="Preferred" vsizetype="Expanding">
          <horstretch>0</horstretch>
          <verstretch>0</verstretch>
         </sizepolicy>
        </property>
        <property name="styleSheet">
         <string notr="true">background-color:#ffdddd;</string>
        </property>
        <property name="text">
         <string>TextLabel</string>
        </property>
       </widget>
      </item>
     </layout>
    </item>
   </layout>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>21</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <customwidgets>
  <customwidget>
   <class>ElidedLabel</class>
   <extends>QFrame</extends>
   <header>elidedlabel.h</header>
   <container>1</container>
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>