Formatting Magic in Qt: Dive Deeper with QTextCursor, QTextDocument, and Inline Formatting

Purpose

• Formatting information encompasses various visual attributes that can be applied to text, including font properties (family, size, weight), foreground and background colors, alignment, indentation, and more.
• Text objects in Qt represent elements that group parts of a document together, such as lists, frames, or tables.
• In Qt's rich text processing framework, QTextObject::format() is a const member function used to retrieve the formatting information associated with a specific text object within a QTextDocument.

Usage

1. • To work with text objects and formatting, you'll need to include the QTextDocument header:

     #include <QTextDocument>
     

2. Create a Text Object (Usually Indirectly)
   

   • You typically don't create text objects directly. Instead, they are managed by the QTextDocument class. When you create a list, frame, or table within the document, a corresponding text object is automatically created behind the scenes.

3. Get a Reference to the Text Object
   

   • You might obtain a reference to a text object using methods like currentTextObject() on a QTextCursor or iterating through the document's text objects.

4. Call format()
   

   • Once you have a reference to the text object, call its format() function to retrieve the associated QTextFormat object:

     QTextObject* textObject = ...; // Get a reference to the text object
     QTextFormat format = textObject->format();
     

Returned QTextFormat Object

• You can use the various member functions of QTextFormat to:
  • Access specific formatting properties (e.g., fontProperty(), foreground(), alignment())
  • Modify existing formatting properties
  • Create a new format object with different settings
• The QTextFormat object returned by format() encapsulates the formatting properties applied to the text object.

Example (Modifying Font Boldness)

QTextObject* textObject = ...; // Get the text object reference
QTextFormat format = textObject->format();

// Check if the font is currently bold
if (format.fontProperty().boldWeight() == QFont::Bold) {
    format.setFontWeight(QFont::Normal); // Make it non-bold
} else {
    format.setFontWeight(QFont::Bold);   // Make it bold
}

textObject->setFormat(format); // Apply the modified format back to the text object

Additional Notes

• Consider using formatIndex() along with QTextDocument::allFormats() to retrieve a list of all formatting objects used in the document and potentially modify them.
• QTextObject is a base class for various text objects like QTextList, QTextFrame, and QTextTable. The specific formatting properties available in the returned QTextFormat will depend on the type of text object.

---

#include <QApplication>
#include <QWidget>
#include <QHBoxLayout>
#include <QTextEdit>
#include <QPushButton>
#include <QTextCursor>
#include <QTextFormat>

class TextFormattingExample : public QWidget {
    Q_OBJECT

public:
    TextFormattingExample(QWidget *parent = nullptr) : QWidget(parent) {
        // Create layout and widgets
        auto layout = new QHBoxLayout(this);
        textEdit = new QTextEdit;
        boldButton = new QPushButton("Bold");
        italicButton = new QPushButton("Italic");

        // Connect buttons to slots
        connect(boldButton, &QPushButton::clicked, this, &TextFormattingExample::toggleBold);
        connect(italicButton, &QPushButton::clicked, this, &TextFormattingExample::toggleItalic);

        // Add widgets to layout
        layout->addWidget(textEdit);
        layout->addWidget(boldButton);
        layout->addWidget(italicButton);

        setLayout(layout);
    }

private slots:
    void toggleBold() {
        QTextCursor cursor = textEdit->textCursor();
        if (cursor.hasSelection()) {
            // Get the format of the selected text
            QTextFormat format = cursor.currentTextObject()->format();

            // Toggle font weight (bold or normal)
            format.setFontWeight(format.fontProperty().boldWeight() == QFont::Bold ? QFont::Normal : QFont::Bold);

            // Apply the modified format back to the selection
            cursor.setCharFormat(format);
        }
    }

    void toggleItalic() {
        QTextCursor cursor = textEdit->textCursor();
        if (cursor.hasSelection()) {
            // Get the format of the selected text
            QTextFormat format = cursor.currentTextObject()->format();

            // Toggle font italic (on or off)
            format.setFontItalic(!format.fontProperty().italic());

            // Apply the modified format back to the selection
            cursor.setCharFormat(format);
        }
    }

private:
    QTextEdit *textEdit;
    QPushButton *boldButton, *italicButton;
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    TextFormattingExample example;
    example.show();
    return app.exec();
}

1. • Necessary headers (QApplication, QWidget, QHBoxLayout, QTextEdit, QPushButton, QTextCursor, QTextFormat) are included.
   • The TextFormattingExample class inherits from QWidget and provides functionalities for text formatting.

2. Constructor
   

   • Creates a layout, QTextEdit, and two QPushButtons.
   • Connects button clicks to corresponding slots (toggleBold and toggleItalic).
   • Sets the layout for the widget.

3. toggleItalic Slot
   

   • Similar to toggleBold, but toggles font italic using format.setFontItalic().

4. main Function
   

   • Creates a QApplication object and an instance of TextFormattingExample.
   • Shows the widget and runs the application event loop.

Improvements

• It demonstrates formatting a text selection instead of the entire document.
• This example uses a QTextEdit for user interaction.

---

QTextCursor::charFormat()

• It's more concise for situations where you don't need to specifically access a text object.
• If you're working with a text selection or the current character position, you can use QTextCursor::charFormat().

Example

QTextCursor cursor = textEdit->textCursor(); // Get the cursor
QTextFormat format = cursor.charFormat(); // Get format at cursor position

// Or, if there's a selection:
if (cursor.hasSelection()) {
  format = cursor.charFormat(); // Get format of the selection
}

QTextDocument::allFormats()

• You can then loop through the list and inspect or modify the formatting information as needed.
• This method returns a list of QTextFormat objects.
• If you need to iterate through all formatting objects used in the entire document, you can use QTextDocument::allFormats().

Example

QTextDocument* document = textEdit->document(); // Get the document
QList<QTextFormat> allFormats = document->allFormats();

// Loop through all formatting objects
for (const QTextFormat& format : allFormats) {
  // Access specific properties (e.g., font, color)
  QFont font = format.fontProperty();
  QColor foreground = format.foreground();
}

Inline Formatting with QTextCharFormat

• This approach is useful when creating formatted text dynamically or applying formatting to specific characters.
• For basic formatting within a specific piece of text, you can directly set inline formatting using QTextCharFormat.

Example

QString formattedText = "This is ";
QTextCharFormat boldFormat;
boldFormat.setFontWeight(QFont::Bold);

formattedText.append("<span style=\" font-weight: bold; \">bold</span>"); // Inline style using HTML-like syntax

QTextEdit* textEdit = new QTextEdit;
textEdit->setText(formattedText); // Set formatted text

The choice of method depends on your specific needs:

• Use inline formatting with QTextCharFormat for applying formatting directly to specific text content.
• Use QTextDocument::allFormats() to iterate through all formatting objects in the document.
• Use QTextCursor::charFormat() for quick retrieval of formatting at the cursor position or within a selection.
• Use QTextObject::format() when you need to access the formatting associated with a specific text object in the document structure.