QPlainTextEdit Class

QPlainTextEdit is an advanced viewer/editor supporting plain text. It is optimized to handle large documents and to respond quickly to user input.

QPlainText uses very much the same technology and concepts as QTextEdit, but is optimized for plain text handling.

QPlainTextEdit works on paragraphs and characters. A paragraph is a formatted string which is word-wrapped to fit into the width of the widget. By default when reading plain text, one newline signifies a paragraph. A document consists of zero or more paragraphs. Paragraphs are separated by hard line breaks. Each character within a paragraph has its own attributes, for example, font and color.

The shape of the mouse cursor on a QPlainTextEdit is Qt::IBeamCursor by default. It can be changed through the viewport()'s cursor property.

The text is set or replaced using setPlainText() which deletes the existing text and replaces it with the text passed to setPlainText().

Text can be inserted using the QTextCursor class or using the convenience functions insertPlainText(), appendPlainText() or paste().

By default, the text edit wraps words at whitespace to fit within the text edit widget. The setLineWrapMode() function is used to specify the kind of line wrap you want, WidgetWidth or NoWrap if you don't want any wrapping. If you use word wrap to the widget's width WidgetWidth, you can specify whether to break on whitespace or anywhere with setWordWrapMode().

The find() function can be used to find and select a given string within the text.

If you want to limit the total number of paragraphs in a QPlainTextEdit, as it is for example useful in a log viewer, then you can use the maximumBlockCount property. The combination of setMaximumBlockCount() and appendPlainText() turns QPlainTextEdit into an efficient viewer for log text. The scrolling can be reduced with the centerOnScroll() property, making the log viewer even faster. Text can be formatted in a limited way, either using a syntax highlighter (see below), or by appending html-formatted text with appendHtml(). While QPlainTextEdit does not support complex rich text rendering with tables and floats, it does support limited paragraph-based formatting that you may need in a log viewer.

Read-only Key Bindings▲

All the information about using QPlainTextEdit as a display widget also applies here.

Selection of text is handled by the QTextCursor class, which provides functionality for creating selections, retrieving the text contents or deleting selections. You can retrieve the object that corresponds with the user-visible cursor using the textCursor() method. If you want to set a selection in QPlainTextEdit just create one on a QTextCursor object and then make that cursor the visible cursor using setCursor(). The selection can be copied to the clipboard with copy(), or cut to the clipboard with cut(). The entire text can be selected using selectAll().

QPlainTextEdit holds a QTextDocument object which can be retrieved using the document() method. You can also set your own document object using setDocument(). QTextDocument emits a textChanged() signal if the text changes and it also provides a isModified() function which will return true if the text has been modified since it was either loaded or since the last call to setModified with false as argument. In addition it provides methods for undo and redo.

Syntax Highlighting▲

Editing Key Bindings▲

QPlainTextEdit is a thin class, implemented by using most of the technology that is behind QTextEdit and QTextDocument. Its performance benefits over QTextEdit stem mostly from using a different and simplified text layout called QPlainTextDocumentLayout on the text document (see QTextDocument::setDocumentLayout()). The plain text document layout does not support tables nor embedded frames, and replaces a pixel-exact height calculation with a line-by-line respectively paragraph-by-paragraph scrolling approach. This makes it possible to handle significantly larger documents, and still resize the editor with line wrap enabled in real time. It also makes for a fast log viewer (see setMaximumBlockCount()).

See also QTextDocument, QTextCursor, Qt Widgets - Application Example, Code Editor Example, Syntax Highlighter Example, Rich Text Processing

This property holds whether the palette background is visible outside the document area

If set to true, the plain text edit paints the palette background on the viewport area not covered by the text document. Otherwise, if set to false, it won't. The feature makes it possible for the user to visually distinguish between the area of the document, painted with the base color of the palette, and the empty area not covered by any document.

The default is false.

Access functions:

• bool backgroundVisible() const

• void setBackgroundVisible(bool visible)

This property holds the number of text blocks in the document.

By default, in an empty document, this property contains a value of 1.

Access functions:

• int blockCount() const

This property holds whether the cursor should be centered on screen

If set to true, the plain text edit scrolls the document vertically to make the cursor visible at the center of the viewport. This also allows the text edit to scroll below the end of the document. Otherwise, if set to false, the plain text edit scrolls the smallest amount possible to ensure the cursor is visible. The same algorithm is applied to any new line appended through appendPlainText().

The default is false.

Access functions:

• bool centerOnScroll() const

• void setCenterOnScroll(bool enabled)

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This property specifies the width of the cursor in pixels. The default value is 1.

Access functions:

• int cursorWidth() const

• void setCursorWidth(int width)

This property holds the title of the document parsed from the text.

By default, this property contains an empty string.

Access functions:

• documentTitle() const

• void setDocumentTitle(const &title)

This property holds the line wrap mode

The default mode is WidgetWidth which causes words to be wrapped at the right edge of the text edit. Wrapping occurs at whitespace, keeping whole words intact. If you want wrapping to occur within words use setWordWrapMode().

Access functions:

• lineWrapMode() const

• void setLineWrapMode( mode)

This property holds the limit for blocks in the document.

Specifies the maximum number of blocks the document may have. If there are more blocks in the document that specified with this property blocks are removed from the beginning of the document.

A negative or zero value specifies that the document may contain an unlimited amount of blocks.

The default value is 0.

Note that setting this property will apply the limit immediately to the document contents. Setting this property also disables the undo redo history.

Access functions:

• int maximumBlockCount() const

• void setMaximumBlockCount(int maximum)

This property holds whether text entered by the user will overwrite existing text

As with many text editors, the plain text editor widget can be configured to insert or overwrite existing text with new text entered by the user.

If this property is true, existing text is overwritten, character-for-character by new text; otherwise, text is inserted at the cursor position, displacing existing text.

By default, this property is false (new text does not overwrite existing text).

Access functions:

• bool overwriteMode() const

• void setOverwriteMode(bool overwrite)

This property holds the editor placeholder text

Setting this property makes the editor display a grayed-out placeholder text as long as the document() is empty.

By default, this property contains an empty string.

This property was introduced in Qt 5.3.

Access functions:

• placeholderText() const

• void setPlaceholderText(const &placeholderText)

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This property gets and sets the plain text editor's contents. The previous contents are removed and undo/redo history is reset when this property is set. currentCharFormat() is also reset, unless textCursor() is already at the beginning of the document.

By default, for an editor with no contents, this property contains an empty string.

Access functions:

• toPlainText() const

• void setPlainText(const &text)

Notifier signal:

• void textChanged()

This property holds whether the text edit is read-only

In a read-only text edit the user can only navigate through the text and select text; modifying the text is not possible.

This property's default is false.

Access functions:

• bool isReadOnly() const

• void setReadOnly(bool ro)

This property holds whether Tab changes focus or is accepted as input

In some occasions text edits should not allow the user to input tabulators or change indentation using the Tab key, as this breaks the focus chain. The default is false.

Access functions:

• bool tabChangesFocus() const

• void setTabChangesFocus(bool b)

This property holds the tab stop distance in pixels

By default, this property contains a value of 80 pixels.

Do not set a value less than the horizontalAdvance() of the QChar::VisualTabCharacter character, otherwise the tab-character will be drawn incompletely.

This property was introduced in Qt 5.10.

Access functions:

• qreal tabStopDistance() const

• void setTabStopDistance(qreal distance)

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Specifies how the label should interact with user input if it displays text.

If the flags contain either Qt::LinksAccessibleByKeyboard or Qt::TextSelectableByKeyboard then the focus policy is also automatically set to Qt::ClickFocus.

The default value depends on whether the QPlainTextEdit is read-only or editable.

Access functions:

• textInteractionFlags() const

• void setTextInteractionFlags( flags)

This property holds whether undo and redo are enabled

Users are only able to undo or redo actions if this property is true, and if there is an action that can be undone (or redone).

By default, this property is true.

Access functions:

• bool isUndoRedoEnabled() const

• void setUndoRedoEnabled(bool enable)

This property holds the mode QPlainTextEdit will use when wrapping text by words

By default, this property is set to QTextOption::WrapAtWordBoundaryOrAnywhere.

Access functions:

• wordWrapMode() const

• void setWordWrapMode( policy)

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Constructs an empty QPlainTextEdit with parent parent.

Constructs a QPlainTextEdit with parent parent. The text edit will display the plain text text.

Destructor.

Returns the reference of the anchor at position pos, or an empty string if no anchor exists at that point.

Appends a new paragraph with html to the end of the text edit.

appendPlainText()

Appends a new paragraph with text to the end of the text edit.

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Returns the bounding rectangle of the text block in content coordinates. Translate the rectangle with the contentOffset() to get visual coordinates on the viewport.

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Returns the bounding rectangle of the text block in the block's own coordinates.

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This signal is emitted whenever the block count changes. The new block count is passed in newBlockCount.

This function returns true if the contents of the MIME data object, specified by source, can be decoded and inserted into the document. It is called for example when during a drag operation the mouse enters this widget and it is necessary to determine whether it is possible to accept the drag.

Returns whether text can be pasted from the clipboard into the textedit.

Scrolls the document in order to center the cursor vertically.

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Reimplements: QFrame::changeEvent(QEvent *ev).

Deletes all the text in the text edit.

Notes:

• The undo/redo history is also cleared.

• currentCharFormat() is reset, unless textCursor() is already at the beginning of the document.

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Returns the content's origin in viewport coordinates.

The origin of the content of a plain text edit is always the top left corner of the first visible text block. The content offset is different from (0,0) when the text has been scrolled horizontally, or when the first visible block has been scrolled partially off the screen, i.e. the visible text does not start with the first line of the first visible block, or when the first visible block is the very first block and the editor displays a margin.

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Reimplements: QAbstractScrollArea::contextMenuEvent(QContextMenuEvent *e).

Shows the standard context menu created with createStandardContextMenu().

If you do not want the text edit to have a context menu, you can set its contextMenuPolicy to Qt::NoContextMenu. If you want to customize the context menu, reimplement this function. If you want to extend the standard context menu, reimplement this function, call createStandardContextMenu() and extend the menu returned.

Information about the event is passed in the event object.

void MyQPlainTextEdit::contextMenuEvent(QContextMenuEvent *event)
{
    QMenu *menu = createStandardContextMenu();
    menu->addAction(tr("My Menu Item"));
    //...
    menu->exec(event->globalPos());
    delete menu;
}

Copies any selected text to the clipboard.

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This signal is emitted when text is selected or de-selected in the text edit.

When text is selected this signal will be emitted with yes set to true. If no text has been selected or if the selected text is de-selected this signal is emitted with yes set to false.

If yes is true then copy() can be used to copy the selection to the clipboard. If yes is false then copy() does nothing.

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This function returns a new MIME data object to represent the contents of the text edit's current selection. It is called when the selection needs to be encapsulated into a new QMimeData object; for example, when a drag and drop operation is started, or when data is copied to the clipboard.

If you reimplement this function, note that the ownership of the returned QMimeData object is passed to the caller. The selection can be retrieved by using the textCursor() function.

This function creates the standard context menu which is shown when the user clicks on the text edit with the right mouse button. It is called from the default contextMenuEvent() handler. The popup menu's ownership is transferred to the caller.

We recommend that you use the createStandardContextMenu(QPoint) version instead which will enable the actions that are sensitive to where the user clicked.

This function creates the standard context menu which is shown when the user clicks on the text edit with the right mouse button. It is called from the default contextMenuEvent() handler and it takes the position in document coordinates where the mouse click was. This can enable actions that are sensitive to the position where the user clicked. The popup menu's ownership is transferred to the caller.

This function was introduced in Qt 5.5.

Returns the char format that is used when inserting new text.

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returns a QTextCursor at position pos (in viewport coordinates).

This signal is emitted whenever the position of the cursor changed.

returns a rectangle (in viewport coordinates) that includes the cursor.

returns a rectangle (in viewport coordinates) that includes the cursor of the text edit.

Copies the selected text to the clipboard and deletes it from the text edit.

If there is no selected text nothing happens.

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Returns a pointer to the underlying document.

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Reimplements: QAbstractScrollArea::dragEnterEvent(QDragEnterEvent *event).

Reimplements: QAbstractScrollArea::dragLeaveEvent(QDragLeaveEvent *event).

Reimplements: QAbstractScrollArea::dragMoveEvent(QDragMoveEvent *event).

Reimplements: QAbstractScrollArea::dropEvent(QDropEvent *event).

Ensures that the cursor is visible by scrolling the text edit if necessary.

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Returns previously set extra selections.

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Finds the next occurrence of the string, exp, using the given options. Returns true if exp was found and changes the cursor to select the match; otherwise returns false.

This is an overloaded function.

Finds the next occurrence, matching the regular expression, exp, using the given options. The QTextDocument::FindCaseSensitively option is ignored for this overload, use QRegularExpression::CaseInsensitiveOption instead.

Returns true if a match was found and changes the cursor to select the match; otherwise returns false.

This function was introduced in Qt 5.13.

Returns the first visible block.

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Reimplements: QWidget::focusInEvent(QFocusEvent *event).

Reimplements: QWidget::focusNextPrevChild(bool next).

Reimplements: QWidget::focusOutEvent(QFocusEvent *event).

Returns the paint context for the viewport(), useful only when reimplementing paintEvent().

Reimplements: QWidget::inputMethodEvent(QInputMethodEvent *event).

Reimplements: QWidget::inputMethodQuery(Qt::InputMethodQuery query) const.

This function inserts the contents of the MIME data object, specified by source, into the text edit at the current cursor position. It is called whenever text is inserted as the result of a clipboard paste operation, or when the text edit accepts data from a drag and drop operation.

Convenience slot that inserts text at the current cursor position.

It is equivalent to

edit->textCursor().insertText(text);

Reimplements: QAbstractScrollArea::keyPressEvent(QKeyEvent *e).

Reimplements: QWidget::keyReleaseEvent(QKeyEvent *event).

Loads the resource specified by the given type and name.

This function is an extension of QTextDocument::loadResource().

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Merges the properties specified in modifier into the current character format by calling QTextCursor::mergeCharFormat on the editor's cursor. If the editor has a selection then the properties of modifier are directly applied to the selection.

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This signal is emitted whenever the content of the document changes in a way that affects the modification state. If changed is true, the document has been modified; otherwise it is false.

For example, calling setModified(false) on a document and then inserting text causes the signal to get emitted. If you undo that operation, causing the document to return to its original unmodified state, the signal will get emitted again.

Reimplements: QAbstractScrollArea::mouseDoubleClickEvent(QMouseEvent *e).

Reimplements: QAbstractScrollArea::mouseMoveEvent(QMouseEvent *e).

Reimplements: QAbstractScrollArea::mousePressEvent(QMouseEvent *e).

Reimplements: QAbstractScrollArea::mouseReleaseEvent(QMouseEvent *e).

Moves the cursor by performing the given operation.

If mode is QTextCursor::KeepAnchor, the cursor selects the text it moves over. This is the same effect that the user achieves when they hold down the Shift key and move the cursor with the cursor keys.

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Reimplements: QAbstractScrollArea::paintEvent(QPaintEvent *event).

Pastes the text from the clipboard into the text edit at the current cursor position.

If there is no text in the clipboard nothing happens.

To change the behavior of this function, i.e. to modify what QPlainTextEdit can paste and how it is being pasted, reimplement the virtual canInsertFromMimeData() and insertFromMimeData() functions.

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Convenience function to print the text edit's document to the given printer. This is equivalent to calling the print method on the document directly except that this function also supports QPrinter::Selection as print range.

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Redoes the last operation.

If there is no operation to redo, i.e. there is no redo step in the undo/redo history, nothing happens.

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This signal is emitted whenever redo operations become available (available is true) or unavailable (available is false).

Reimplements: QAbstractScrollArea::resizeEvent(QResizeEvent *event).

Reimplements: QAbstractScrollArea::scrollContentsBy(int dx, int dy).

Selects all text.

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This signal is emitted whenever the selection changes.

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Sets the char format that is be used when inserting new text to format by calling QTextCursor::setCharFormat() on the editor's cursor. If the editor has a selection then the char format is directly applied to the selection.

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Makes document the new document of the text editor.

The parent QObject of the provided document remains the owner of the object. If the current document is a child of the text editor, then it is deleted.

The document must have a document layout that inherits QPlainTextDocumentLayout (see QTextDocument::setDocumentLayout()).

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This function allows temporarily marking certain regions in the document with a given color, specified as selections. This can be useful for example in a programming editor to mark a whole line of text with a given background color to indicate the existence of a breakpoint.

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Changes the text of the text edit to the string text. Any previous text is removed.

text is interpreted as plain text.

Notes:

• The undo/redo history is also cleared.

• currentCharFormat() is reset, unless textCursor() is already at the beginning of the document.

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Sets the visible cursor.

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Reimplements: QWidget::showEvent(QShowEvent *event).

This signal is emitted whenever the document's content changes; for example, when text is inserted or deleted, or when formatting is applied.

Returns a copy of the QTextCursor that represents the currently visible cursor. Note that changes on the returned cursor do not affect QPlainTextEdit's cursor; use setTextCursor() to update the visible cursor.

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Returns the text of the text edit as plain text.

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Undoes the last operation.

If there is no operation to undo, i.e. there is no undo step in the undo/redo history, nothing happens.

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This signal is emitted whenever undo operations become available (available is true) or unavailable (available is false).

This signal is emitted when the text document needs an update of the specified rect. If the text is scrolled, rect will cover the entire viewport area. If the text is scrolled vertically, dy carries the amount of pixels the viewport was scrolled.

The purpose of the signal is to support extra widgets in plain text edit subclasses that e.g. show line numbers, breakpoints, or other extra information.

Reimplements: QAbstractScrollArea::wheelEvent(QWheelEvent *e).

Zooms in on the text by making the base font size range points larger and recalculating all font sizes to be the new size. This does not change the size of any images.

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Zooms out on the text by making the base font size range points smaller and recalculating all font sizes to be the new size. This does not change the size of any images.

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