Inserting New Paragraphs in Qt Text Editing Widgets: QTextCursor::insertBlock()

Purpose

• Inserts a new empty block (paragraph) at the current cursor position within a Qt text editing widget like QTextEdit or QPlainTextEdit.

Overloaded Functions

QTextCursor::insertBlock() offers two options:

1. • insertBlock()
   • Inserts a new block with the formatting attributes inherited from the current block where the cursor resides. This includes block format (margins, spacing, etc.) and character format (font, color, etc.).

2. Custom formatting
   

   • insertBlock(const QTextBlockFormat &format, const QTextCharFormat &charFormat)
   • Allows you to specify the desired QTextBlockFormat for the new block's overall appearance and a separate QTextCharFormat for the text within the block.

Steps Involved

1. (Optional) Custom Formatting
   If using the overloaded function, create QTextBlockFormat and QTextCharFormat objects to define the block's and text's formatting.
2. Cursor Positioning
   Ensure the QTextCursor object is positioned at the desired location where you want to insert the new block.
3. Insertion
   Call insertBlock() (default behavior) or insertBlock(format, charFormat) (custom formatting). This triggers the following actions internally:
   • A temporary edit block is initiated.
   • Any content at the cursor position (if present) is removed.
   • The new block is created with the specified formatting.
   • The cursor position is adjusted to be placed at the start of the newly inserted block.
   • The edit block is finalized.

Example (Default Behavior)

#include <QApplication>
#include <QTextEdit>

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

    QTextEdit editor;
    editor.setPlainText("This is some existing text.\n");

    QTextCursor cursor = editor.textCursor();
    cursor.movePosition(QTextCursor::End, QTextCursor::LineMove, 1); // Move cursor to the end of the first line

    cursor.insertBlock(); // Insert a new empty block at the end of the first line

    editor.show();
    return app.exec();
}

Key Points

• Remember to position the cursor appropriately before calling insertBlock().
• For more granular control over formatting, consider using the overloaded function with custom QTextBlockFormat and QTextCharFormat objects.
• Use insertBlock() when you want to create new paragraphs within your text.

---

#include <QApplication>
#include <QTextEdit>
#include <QTextFormat>

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

    QTextEdit editor;
    editor.setPlainText("This is some existing text.\n");

    QTextCursor cursor = editor.textCursor();
    cursor.movePosition(QTextCursor::End, QTextCursor::LineMove, 1); // Move cursor to the end of the first line

    // Create custom formatting objects
    QTextBlockFormat blockFormat;
    blockFormat.setLeftMargin(30); // Indent new block by 30 pixels

    QTextCharFormat charFormat;
    charFormat.setFontItalic(true); // Make text in new block italic

    cursor.insertBlock(blockFormat, charFormat); // Insert with custom formatting

    editor.show();
    return app.exec();
}

In this example:

1. We create QTextBlockFormat (blockFormat) to set a left margin of 30 pixels for the new block, creating an indentation.
2. We create QTextCharFormat (charFormat) to make the text within the new block italic.
3. We call insertBlock(blockFormat, charFormat) to insert the new block with the defined formatting.

---

QTextDocument::setPlainText() or QTextEdit::setPlainText()

• This approach is simpler but less flexible for targeted insertions within the existing text.
• If you want to completely replace the existing text content with new paragraphs, you can use setPlainText().
  • Set the desired text with newlines (\n) to create paragraphs.

QTextDocument::insertText() or QTextEdit::insertPlainText()

• They lack the fine-grained control over formatting offered by insertBlock().
• Similar to setPlainText(), these methods insert text at the current cursor position.
  • You can include newlines (\n) to create paragraphs.

Manual Block Manipulation (Less Common)

• This is a more complex approach and requires careful handling of text document structure, so it's generally recommended to use the higher-level methods like insertBlock() whenever possible.
• In rare scenarios, you might directly manipulate text blocks using methods like QTextDocument::findBlock() and QTextBlock::insertBlockAfter().

Choosing the Right Approach

• Manual block manipulation is typically reserved for advanced scenarios where finer control over the text document structure is necessary.
• For simple text replacement or insertion without specific formatting, setPlainText() or insertText() might be sufficient.
• If you need to insert new paragraphs with specific formatting control, QTextCursor::insertBlock() is the most suitable choice.

• For more granular control over formatting within the inserted text, you might need to combine these methods with character formatting techniques using QTextCharFormat.
• When using setPlainText() or insertText(), keep in mind that any existing formatting in the replaced or inserted text will be applied based on the default styles or the formatting at the insertion point.