PDF Viewer Example

 // Copyright (C) 2017 Klaralvdalens Datakonsult AB (KDAB).
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 #include "zoomselector.h"

 #include <QLineEdit>

 ZoomSelector::ZoomSelector(QWidget *parent)
     : QComboBox(parent)
 {
     setEditable(true);

     addItem(QLatin1String("Fit Width"));
     addItem(QLatin1String("Fit Page"));
     addItem(QLatin1String("12%"));
     addItem(QLatin1String("25%"));
     addItem(QLatin1String("33%"));
     addItem(QLatin1String("50%"));
     addItem(QLatin1String("66%"));
     addItem(QLatin1String("75%"));
     addItem(QLatin1String("100%"));
     addItem(QLatin1String("125%"));
     addItem(QLatin1String("150%"));
     addItem(QLatin1String("200%"));
     addItem(QLatin1String("400%"));

     connect(this, &QComboBox::currentTextChanged,
             this, &ZoomSelector::onCurrentTextChanged);

     connect(lineEdit(), &QLineEdit::editingFinished,
             this, [this](){onCurrentTextChanged(lineEdit()->text()); });
 }

 void ZoomSelector::setZoomFactor(qreal zoomFactor)
 {
     setCurrentText(QString::number(qRound(zoomFactor * 100)) + QLatin1String("%"));
 }

 void ZoomSelector::reset()
 {
     setCurrentIndex(8); // 100%
 }

 void ZoomSelector::onCurrentTextChanged(const QString &text)
 {
     if (text == QLatin1String("Fit Width")) {
         emit zoomModeChanged(QPdfView::ZoomMode::FitToWidth);
     } else if (text == QLatin1String("Fit Page")) {
         emit zoomModeChanged(QPdfView::ZoomMode::FitInView);
     } else {
         qreal factor = 1.0;

         QString withoutPercent(text);
         withoutPercent.remove(QLatin1Char('%'));

         bool ok = false;
         const int zoomLevel = withoutPercent.toInt(&ok);
         if (ok)
             factor = zoomLevel / 100.0;

         emit zoomModeChanged(QPdfView::ZoomMode::Custom);
         emit zoomFactorChanged(factor);
     }
 }