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QClipboard Class

The QClipboard class provides access to the window system clipboard. More...

Header: #include <QClipboard>
qmake: QT += gui
Inherits: QObject

Public Types

enum Mode { Clipboard, Selection, FindBuffer }

Public Functions

void clear(QClipboard::Mode mode = Clipboard)
QImage image(QClipboard::Mode mode = Clipboard) const
const QMimeData *mimeData(QClipboard::Mode mode = Clipboard) const
bool ownsClipboard() const
bool ownsFindBuffer() const
bool ownsSelection() const
QPixmap pixmap(QClipboard::Mode mode = Clipboard) const
void setImage(const QImage &image, QClipboard::Mode mode = Clipboard)
void setMimeData(QMimeData *src, QClipboard::Mode mode = Clipboard)
void setPixmap(const QPixmap &pixmap, QClipboard::Mode mode = Clipboard)
void setText(const QString &text, QClipboard::Mode mode = Clipboard)
bool supportsFindBuffer() const
bool supportsSelection() const
QString text(QClipboard::Mode mode = Clipboard) const
QString text(QString &subtype, QClipboard::Mode mode = Clipboard) const

Signals

void changed(QClipboard::Mode mode)
void dataChanged()
void findBufferChanged()
void selectionChanged()

Detailed Description

The clipboard offers a simple mechanism to copy and paste data between applications.

QClipboard supports the same data types that QDrag does, and uses similar mechanisms. For advanced clipboard usage read Drag and Drop.

There is a single QClipboard object in an application, accessible as QGuiApplication::clipboard().

Example:

QClipboard *clipboard = QGuiApplication::clipboard();
QString originalText = clipboard->text();
...
clipboard->setText(newText);

QClipboard features some convenience functions to access common data types: setText() allows the exchange of Unicode text and setPixmap() and setImage() allows the exchange of QPixmaps and QImages between applications. The setMimeData() function is the ultimate in flexibility: it allows you to add any QMimeData into the clipboard. There are corresponding getters for each of these, e.g. text(), image() and pixmap(). You can clear the clipboard by calling clear().

A typical example of the use of these functions follows:

void DropArea::paste()
{
    const QClipboard *clipboard = QApplication::clipboard();
    const QMimeData *mimeData = clipboard->mimeData();

    if (mimeData->hasImage()) {
        setPixmap(qvariant_cast<QPixmap>(mimeData->imageData()));
    } else if (mimeData->hasHtml()) {
        setText(mimeData->html());
        setTextFormat(Qt::RichText);
    } else if (mimeData->hasText()) {
        setText(mimeData->text());
        setTextFormat(Qt::PlainText);
    } else {
        setText(tr("Cannot display data"));
    }

Notes for X11 Users

  • The X11 Window System has the concept of a separate selection and clipboard. When text is selected, it is immediately available as the global mouse selection. The global mouse selection may later be copied to the clipboard. By convention, the middle mouse button is used to paste the global mouse selection.
  • X11 also has the concept of ownership; if you change the selection within a window, X11 will only notify the owner and the previous owner of the change, i.e. it will not notify all applications that the selection or clipboard data changed.
  • Lastly, the X11 clipboard is event driven, i.e. the clipboard will not function properly if the event loop is not running. Similarly, it is recommended that the contents of the clipboard are stored or retrieved in direct response to user-input events, e.g. mouse button or key presses and releases. You should not store or retrieve the clipboard contents in response to timer or non-user-input events.
  • Since there is no standard way to copy and paste files between applications on X11, various MIME types and conventions are currently in use. For instance, Nautilus expects files to be supplied with a x-special/gnome-copied-files MIME type with data beginning with the cut/copy action, a newline character, and the URL of the file.

Notes for macOS Users

macOS supports a separate find buffer that holds the current search string in Find operations. This find clipboard can be accessed by specifying the FindBuffer mode.

Notes for Windows and macOS Users

  • Windows and macOS do not support the global mouse selection; they only supports the global clipboard, i.e. they only add text to the clipboard when an explicit copy or cut is made.
  • Windows and macOS does not have the concept of ownership; the clipboard is a fully global resource so all applications are notified of changes.

Notes for Universal Windows Platform Users

  • The Universal Windows Platform only allows to query the clipboard in case the application is active and an application window has focus. Accessing the clipboard data when in background will fail due to access denial.

See also QGuiApplication.

Member Type Documentation

enum QClipboard::Mode

This enum type is used to control which part of the system clipboard is used by QClipboard::mimeData(), QClipboard::setMimeData() and related functions.

ConstantValueDescription
QClipboard::Clipboard0indicates that data should be stored and retrieved from the global clipboard.
QClipboard::Selection1indicates that data should be stored and retrieved from the global mouse selection. Support for Selection is provided only on systems with a global mouse selection (e.g. X11).
QClipboard::FindBuffer2indicates that data should be stored and retrieved from the Find buffer. This mode is used for holding search strings on macOS.

See also QClipboard::supportsSelection().

Member Function Documentation

[signal] void QClipboard::changed(QClipboard::Mode mode)

This signal is emitted when the data for the given clipboard mode is changed.

This function was introduced in Qt 4.2.

See also dataChanged(), selectionChanged(), and findBufferChanged().

[signal] void QClipboard::dataChanged()

This signal is emitted when the clipboard data is changed.

On macOS and with Qt version 4.3 or higher, clipboard changes made by other applications will only be detected when the application is activated.

See also findBufferChanged(), selectionChanged(), and changed().

[signal] void QClipboard::findBufferChanged()

This signal is emitted when the find buffer is changed. This only applies to macOS.

With Qt version 4.3 or higher, clipboard changes made by other applications will only be detected when the application is activated.

This function was introduced in Qt 4.2.

See also dataChanged(), selectionChanged(), and changed().

[signal] void QClipboard::selectionChanged()

This signal is emitted when the selection is changed. This only applies to windowing systems that support selections, e.g. X11. Windows and macOS don't support selections.

See also dataChanged(), findBufferChanged(), and changed().

void QClipboard::clear(QClipboard::Mode mode = Clipboard)

Clear the clipboard contents.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, this function clears the global clipboard contents. If mode is QClipboard::Selection, this function clears the global mouse selection contents. If mode is QClipboard::FindBuffer, this function clears the search string buffer.

See also QClipboard::Mode and supportsSelection().

QImage QClipboard::image(QClipboard::Mode mode = Clipboard) const

Returns the clipboard image, or returns a null image if the clipboard does not contain an image or if it contains an image in an unsupported image format.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the image is retrieved from the global clipboard. If mode is QClipboard::Selection, the image is retrieved from the global mouse selection.

See also setImage(), pixmap(), mimeData(), and QImage::isNull().

const QMimeData *QClipboard::mimeData(QClipboard::Mode mode = Clipboard) const

Returns a pointer to a QMimeData representation of the current clipboard data (can be nullptr if the given mode is not supported by the platform).

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the data is retrieved from the global clipboard. If mode is QClipboard::Selection, the data is retrieved from the global mouse selection. If mode is QClipboard::FindBuffer, the data is retrieved from the search string buffer.

The text(), image(), and pixmap() functions are simpler wrappers for retrieving text, image, and pixmap data.

Note: The pointer returned might become invalidated when the contents of the clipboard changes; either by calling one of the setter functions or externally by the system clipboard changing.

See also setMimeData().

bool QClipboard::ownsClipboard() const

Returns true if this clipboard object owns the clipboard data; otherwise returns false.

bool QClipboard::ownsFindBuffer() const

Returns true if this clipboard object owns the find buffer data; otherwise returns false.

This function was introduced in Qt 4.2.

bool QClipboard::ownsSelection() const

Returns true if this clipboard object owns the mouse selection data; otherwise returns false.

QPixmap QClipboard::pixmap(QClipboard::Mode mode = Clipboard) const

Returns the clipboard pixmap, or null if the clipboard does not contain a pixmap. Note that this can lose information. For example, if the image is 24-bit and the display is 8-bit, the result is converted to 8 bits, and if the image has an alpha channel, the result just has a mask.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the pixmap is retrieved from the global clipboard. If mode is QClipboard::Selection, the pixmap is retrieved from the global mouse selection.

See also setPixmap(), image(), mimeData(), and QPixmap::convertFromImage().

void QClipboard::setImage(const QImage &image, QClipboard::Mode mode = Clipboard)

Copies the image into the clipboard.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the image is stored in the global clipboard. If mode is QClipboard::Selection, the data is stored in the global mouse selection.

This is shorthand for:

QMimeData *data = new QMimeData;
data->setImageData(image);
clipboard->setMimeData(data, mode);

See also image(), setPixmap(), and setMimeData().

void QClipboard::setMimeData(QMimeData *src, QClipboard::Mode mode = Clipboard)

Sets the clipboard data to src. Ownership of the data is transferred to the clipboard. If you want to remove the data either call clear() or call setMimeData() again with new data.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the data is stored in the global clipboard. If mode is QClipboard::Selection, the data is stored in the global mouse selection. If mode is QClipboard::FindBuffer, the data is stored in the search string buffer.

The setText(), setImage() and setPixmap() functions are simpler wrappers for setting text, image and pixmap data respectively.

See also mimeData().

void QClipboard::setPixmap(const QPixmap &pixmap, QClipboard::Mode mode = Clipboard)

Copies pixmap into the clipboard. Note that this is slower than setImage() because it needs to convert the QPixmap to a QImage first.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the pixmap is stored in the global clipboard. If mode is QClipboard::Selection, the pixmap is stored in the global mouse selection.

See also pixmap(), setImage(), and setMimeData().

void QClipboard::setText(const QString &text, QClipboard::Mode mode = Clipboard)

Copies text into the clipboard as plain text.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the text is stored in the global clipboard. If mode is QClipboard::Selection, the text is stored in the global mouse selection. If mode is QClipboard::FindBuffer, the text is stored in the search string buffer.

See also text() and setMimeData().

bool QClipboard::supportsFindBuffer() const

Returns true if the clipboard supports a separate search buffer; otherwise returns false.

bool QClipboard::supportsSelection() const

Returns true if the clipboard supports mouse selection; otherwise returns false.

QString QClipboard::text(QClipboard::Mode mode = Clipboard) const

Returns the clipboard text as plain text, or an empty string if the clipboard does not contain any text.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the text is retrieved from the global clipboard. If mode is QClipboard::Selection, the text is retrieved from the global mouse selection. If mode is QClipboard::FindBuffer, the text is retrieved from the search string buffer.

See also setText() and mimeData().

QString QClipboard::text(QString &subtype, QClipboard::Mode mode = Clipboard) const

This is an overloaded function.

Returns the clipboard text in subtype subtype, or an empty string if the clipboard does not contain any text. If subtype is null, any subtype is acceptable, and subtype is set to the chosen subtype.

The mode argument is used to control which part of the system clipboard is used. If mode is QClipboard::Clipboard, the text is retrieved from the global clipboard. If mode is QClipboard::Selection, the text is retrieved from the global mouse selection.

Common values for subtype are "plain" and "html".

Note that calling this function repeatedly, for instance from a key event handler, may be slow. In such cases, you should use the dataChanged() signal instead.

See also setText() and mimeData().

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