Qt Widgets: Unveiling QFontDialog::open() for Font Selection

Purpose

• Provides options to customize the font's attributes (family, size, style, etc.).
• Presents a modal dialog to the user, allowing them to select a font.

Functionality

1. Creation
   You don't directly create a QFontDialog object using new. Instead, use the static function QFontDialog::getFont():

   QFont initialFont("Arial", 10); // Example initial font
   bool ok;
   QFont selectedFont = QFontDialog::getFont(ok, initialFont, this);
   

   • ok (output parameter): A boolean indicating whether the user clicked OK (true) or Cancel (false).
   • initialFont (optional): The font to display initially in the dialog.
   • this (optional): The parent widget for the dialog (often the current widget).

2. Opening the Dialog
   

   • The open() function is an overloaded function with different forms:

     • open(QObject *receiver, const char *member):
       • Connects the dialog's fontSelected() signal to a slot specified by receiver and member.
       • Disconnects the signal when the dialog closes.

   Example
   

   void handleFontSelection(const QFont& font) {
       // Handle selected font here
       qDebug() << "Selected font:" << font;
   }
   
   QFontDialog fontDialog;
   fontDialog.setCurrentFont(initialFont); // Set initial font
   connect(&fontDialog, &QFontDialog::fontSelected, this, &handleFontSelection);
   fontDialog.open();
   

   • In this example, the handleFontSelection() slot is called with the selected font when the user clicks OK.

Customization (Optional)

• Use methods like setCurrentFont(), setOptions(), and setOption() to control the dialog's appearance and behavior:
  • setCurrentFont(): Set the initial font displayed in the dialog.
  • setOptions(): Enable/disable various font selection options (e.g., bold, italic, underline).
  • setOption(): Enable/disable specific font selection options.

Return Value

• None. However, you can use the selectedFont() function after the dialog closes to retrieve the user-selected font (if they clicked OK).

Additional Notes

• Consider using the getFont() function as it simplifies the process of creating and opening the dialog, handling OK/Cancel results, and retrieving the selected font.
• The fontSelected() signal is emitted when the user selects a font (regardless of whether they click OK or Cancel). However, selectedFont() only provides the chosen font if the user clicked OK.

---

Simple Font Selection with getFont()

#include <QApplication>
#include <QFontDialog>
#include <QFont>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QFont initialFont("Times New Roman", 14);

    bool ok;
    QFont selectedFont = QFontDialog::getFont(ok, initialFont);

    if (ok) {
        qDebug() << "Selected font:" << selectedFont;
    } else {
        qDebug() << "User canceled font selection.";
    }

    return app.exec();
}

This code creates a simple application that opens the font dialog using getFont(). It checks the ok flag to determine if the user selected a font or canceled.

Connecting fontSelected() Signal

#include <QApplication>
#include <QFontDialog>
#include <QFont>
#include <QLabel>

void handleFontSelection(const QFont& font) {
    QLabel label("Selected Font:");
    label.setFont(font);
    label.show();
}

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QFontDialog fontDialog;
    connect(&fontDialog, &QFontDialog::fontSelected, nullptr, &handleFontSelection);
    fontDialog.open();

    return app.exec();
}

This code opens the font dialog and connects its fontSelected() signal to a slot handleFontSelection(). This slot displays a label with the selected font when the user clicks OK.

#include <QApplication>
#include <QFontDialog>
#include <QFont>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QFont initialFont("Arial", 12);
    initialFont.setBold(true);

    QFontDialog fontDialog;
    fontDialog.setCurrentFont(initialFont);
    fontDialog.setOptions(QFontDialog::Bold | QFontDialog::Italic);

    bool ok;
    QFont selectedFont = QFontDialog::getFont(ok, initialFont);

    if (ok) {
        qDebug() << "Selected font:" << selectedFont;
    } else {
        qDebug() << "User canceled font selection.";
    }

    return app.exec();
}

---

QComboBox with Font List

• Connect the currentIndexChanged() signal to a slot that sets the font on a target widget (e.g., QLabel).
• Optionally, include font sizes and styles in the displayed text.
• Populate the combobox with available fonts using QFontDatabase::families().
• Create a QComboBox widget.

Example

#include <QApplication>
#include <QComboBox>
#include <QFont>
#include <QFontDatabase>
#include <QLabel>

void updateFont(const QString& fontName) {
  QFont font(fontName);
  label.setFont(font);
}

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  QComboBox fontComboBox;
  QStringList fonts = QFontDatabase::families();

  for (const QString& font : fonts) {
    fontComboBox.addItem(font);
  }

  QLabel label("Sample Text");

  connect(&fontComboBox, &QComboBox::currentIndexChanged, nullptr, &updateFont);

  fontComboBox.show();
  label.show();

  return app.exec();
}

Advantages

• Compact UI element.
• Simpler implementation.

Disadvantages

• Doesn't provide visual previews of fonts.
• Limited customization compared to QFontDialog.

QFontComboBox

• Emits a currentFontChanged() signal for handling font changes.
• Offers a dropdown with font names, sizes, and styles.
• Qt provides the QFontComboBox widget specifically designed for font selection.

Example

#include <QApplication>
#include <QFontComboBox>
#include <QFont>
#QLabel>

void updateFont(const QFont& font) {
  label.setFont(font);
}

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  QFontComboBox fontComboBox;
  QFont initialFont("Arial", 12);
  fontComboBox.setCurrentFont(initialFont);

  QLabel label("Sample Text");

  connect(&fontComboBox, &QFontComboBox::currentFontChanged, nullptr, &updateFont);

  fontComboBox.show();
  label.show();

  return app.exec();
}

Advantages

• Easier to integrate with existing UI layouts.
• More comprehensive font selection options than QComboBox.

Disadvantages

• Less flexibility than QFontDialog for advanced customization.

Custom Font Selection Widget

• Emit a custom signal when the font is changed.
• Connect these controls to functions that modify a QFont object.
• Create a custom widget with buttons, sliders, or other controls to adjust font properties.

Advantages

• Provides complete control over the UI and behavior.

• Might not be as user-friendly as pre-built options.
• Requires more development effort.