mainwindow.cpp Example File

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 #include <QtWidgets>

 #include "mainwindow.h"
 #include "encodingdialog.h"
 #include "previewform.h"

 MainWindow::MainWindow()
 {
     textEdit = new QPlainTextEdit;
     textEdit->setLineWrapMode(QPlainTextEdit::NoWrap);
     setCentralWidget(textEdit);

     findCodecs();

     previewForm = new PreviewForm(this);
     previewForm->setCodecList(codecs);

     createMenus();

     setWindowTitle(tr("Codecs"));

     const QRect screenGeometry = QApplication::desktop()->screenGeometry(this);
     resize(screenGeometry.width() / 2, screenGeometry.height() * 2 / 3);
 }

 void MainWindow::open()
 {
     const QString fileName = QFileDialog::getOpenFileName(this);
     if (fileName.isEmpty())
         return;
     QFile file(fileName);
     if (!file.open(QFile::ReadOnly)) {
         QMessageBox::warning(this, tr("Codecs"),
                              tr("Cannot read file %1:\n%2")
                              .arg(QDir::toNativeSeparators(fileName),
                                   file.errorString()));
         return;
     }

     const QByteArray data = file.readAll();

     previewForm->setWindowTitle(tr("Choose Encoding for %1").arg(QFileInfo(fileName).fileName()));
     previewForm->setEncodedData(data);
     if (previewForm->exec())
         textEdit->setPlainText(previewForm->decodedString());
 }

 void MainWindow::save()
 {
     const QAction *action = qobject_cast<const QAction *>(sender());
     const QByteArray codecName = action->data().toByteArray();
     const QString title = tr("Save As (%1)").arg(QLatin1String(codecName));

     QString fileName = QFileDialog::getSaveFileName(this, title);
     if (fileName.isEmpty())
         return;
     QFile file(fileName);
     if (!file.open(QFile::WriteOnly | QFile::Text)) {
         QMessageBox::warning(this, tr("Codecs"),
                              tr("Cannot write file %1:\n%2")
                              .arg(QDir::toNativeSeparators(fileName),
                                   file.errorString()));
         return;
     }

     QTextStream out(&file);
     out.setCodec(codecName.constData());
     out << textEdit->toPlainText();
 }

 void MainWindow::about()
 {
     QMessageBox::about(this, tr("About Codecs"),
             tr("The <b>Codecs</b> example demonstrates how to read and write "
                "files using various encodings."));
 }

 void MainWindow::aboutToShowSaveAsMenu()
 {
     QString currentText = textEdit->toPlainText();

     foreach (QAction *action, saveAsActs) {
         QByteArray codecName = action->data().toByteArray();
         QTextCodec *codec = QTextCodec::codecForName(codecName);
         action->setVisible(codec && codec->canEncode(currentText));
     }
 }

 void MainWindow::findCodecs()
 {
     QMap<QString, QTextCodec *> codecMap;
     QRegularExpression iso8859RegExp("^ISO[- ]8859-([0-9]+).*$");
     QRegularExpressionMatch match;

     foreach (int mib, QTextCodec::availableMibs()) {
         QTextCodec *codec = QTextCodec::codecForMib(mib);

         QString sortKey = codec->name().toUpper();
         int rank;

         if (sortKey.startsWith(QLatin1String("UTF-8"))) {
             rank = 1;
         } else if (sortKey.startsWith(QLatin1String("UTF-16"))) {
             rank = 2;
         } else if ((match = iso8859RegExp.match(sortKey)).hasMatch()) {
             if (match.captured(1).size() == 1)
                 rank = 3;
             else
                 rank = 4;
         } else {
             rank = 5;
         }
         sortKey.prepend(QLatin1Char('0' + rank));

         codecMap.insert(sortKey, codec);
     }
     codecs = codecMap.values();
 }

 void MainWindow::createMenus()
 {
     QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
     QAction *openAct =
         fileMenu->addAction(tr("&Open..."), this, &MainWindow::open);
     openAct->setShortcuts(QKeySequence::Open);

     QMenu *saveAsMenu = fileMenu->addMenu(tr("&Save As"));
     connect(saveAsMenu, &QMenu::aboutToShow,
             this, &MainWindow::aboutToShowSaveAsMenu);
     foreach (const QTextCodec *codec, codecs) {
         const QByteArray name = codec->name();
         QAction *action = saveAsMenu->addAction(tr("%1...").arg(QLatin1String(name)));
         action->setData(QVariant(name));
         connect(action, &QAction::triggered, this, &MainWindow::save);
         saveAsActs.append(action);
     }

     fileMenu->addSeparator();
     QAction *exitAct = fileMenu->addAction(tr("E&xit"), this, &QWidget::close);
     exitAct->setShortcuts(QKeySequence::Quit);

     auto toolMenu =  menuBar()->addMenu(tr("&Tools"));
     auto encodingAction = toolMenu->addAction(tr("Encodings"), this, &MainWindow::encodingDialog);
     encodingAction->setShortcut(Qt::CTRL + Qt::Key_E);
     encodingAction->setToolTip(tr("Shows a dialog allowing to convert to common encoding in programming languages."));

     menuBar()->addSeparator();

     QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));
     helpMenu->addAction(tr("&About"), this, &MainWindow::about);
     helpMenu->addAction(tr("About &Qt"), qApp, &QApplication::aboutQt);
 }

 void MainWindow::encodingDialog()
 {
     if (!m_encodingDialog) {
         m_encodingDialog = new EncodingDialog(this);
         const QRect screenGeometry = QApplication::desktop()->screenGeometry(this);
         m_encodingDialog->setMinimumWidth(screenGeometry.width() / 4);
     }
     m_encodingDialog->show();
     m_encodingDialog->raise();

 }