The QDrag class provides support for MIME-based drag and drop data transfer. More...

#include <qdrag.h>

Inheritance diagram for QDrag:

Signals
void	actionChanged (Qt::DropAction action)
	This signal is emitted when the action associated with the drag changes. More...

void	targetChanged (QWidget *newTarget)
	This signal is emitted when the target of the drag and drop operation changes, with newTarget the new target. More...

Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More...

Public Functions
Qt::DropAction	exec (Qt::DropActions supportedActions=Qt::MoveAction)
	Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed. More...

Qt::DropAction	exec (Qt::DropActions supportedActions, Qt::DropAction defaultAction)
	Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed. More...

QPoint	hotSpot () const
	Returns the position of the hot spot relative to the top-left corner of the cursor. More...

QMimeData *	mimeData () const
	Returns the MIME data that is encapsulated by the drag object. More...

QPixmap	pixmap () const
	Returns the pixmap used to represent the data in a drag and drop operation. More...

	QDrag (QWidget *dragSource)
	Constructs a new drag object for the widget specified by dragSource. More...

void	setDragCursor (const QPixmap &cursor, Qt::DropAction action)
	Sets the drag cursor for the action. More...

void	setHotSpot (const QPoint &hotspot)
	Sets the position of the hot spot relative to the top-left corner of the pixmap used to the point specified by hotspot. More...

void	setMimeData (QMimeData *data)
	Sets the data to be sent to the given MIME data. More...

void	setPixmap (const QPixmap &)
	Sets pixmap as the pixmap used to represent the data in a drag and drop operation. More...

QWidget *	source () const
	Returns the source of the drag object. More...

Qt::DropAction	start (Qt::DropActions supportedActions=Qt::CopyAction)
	Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed. More...

QWidget *	target () const
	Returns the target of the drag and drop operation. More...

	~QDrag ()
	Destroys the drag object. More...

Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More...

const QObjectList &	children () const
	Returns a list of child objects. More...

bool	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=0, const QObject receiver=0, const char *member=0)

bool	disconnect (const QObject receiver, const char member=0)

void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More...

void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More...

QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More...

virtual bool	event (QEvent *)
	This virtual function receives events to an object and should return true if the event e was recognized and processed. More...

virtual bool	eventFilter (QObject , QEvent )
	Filters events if this object has been installed as an event filter for the watched object. More...

template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More...

template<typename T >
QList< T >	findChildren (const QString &aName=QString()) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. More...

template<typename T >
QList< T >	findChildren (const QRegExp &re) const

bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false. More...

void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More...

bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More...

void	killTimer (int id)
	Kills the timer with timer identifier, id. More...

virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More...

void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More...

QString	objectName () const

QObject *	parent () const
	Returns a pointer to the parent object. More...

QVariant	property (const char *name) const
	Returns the value of the object's name property. More...

Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More...

void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More...

void	setObjectName (const QString &name)

void	setParent (QObject *)
	Makes the object a child of parent. More...

bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value. More...

void	setUserData (uint id, QObjectUserData *data)

bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More...

int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More...

QThread *	thread () const
	Returns the thread in which the object lives. More...

QObjectUserData *	userData (uint id) const

virtual	~QObject ()
	Destroys the object, deleting all its child objects. More...

Friends
class	QDragManager

class	QWidgetPrivate

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More...

Static Public Functions inherited from QObject
static bool	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More...

static bool	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)
	Disconnects signal in object sender from method in object receiver. More...

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static uint	registerUserData ()

static QString	tr (const char sourceText, const char comment=0, int n=-1)

static QString	trUtf8 (const char sourceText, const char comment=0, int n=-1)

Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More...

Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More...

virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More...

virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More...

virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More...

	QObject (QObjectPrivate &dd, QObject *parent=0)

int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More...

QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. More...

int	senderSignalIndex () const

virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More...

Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject

Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()

T *	qobject_cast (QObject *object)

	QObjectList

void *	qt_find_obj_child (QObject parent, const char type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More...

Detailed Description

The QDrag class provides support for MIME-based drag and drop data transfer.

Drag and drop is an intuitive way for users to copy or move data around in an application, and is used in many desktop environments as a mechanism for copying data between applications. Drag and drop support in Qt is centered around the QDrag class that handles most of the details of a drag and drop operation.

The data to be transferred by the drag and drop operation is contained in a QMimeData object. This is specified with the setMimeData() function in the following way:

        QDrag *drag = new QDrag(this);
        QMimeData *mimeData = new QMimeData;
        mimeData->setText(commentEdit->toPlainText());
        drag->setMimeData(mimeData);

Note that setMimeData() assigns ownership of the QMimeData object to the QDrag object. The QDrag must be constructed on the heap with a parent QWidget to ensure that Qt can clean up after the drag and drop operation has been completed.

A pixmap can be used to represent the data while the drag is in progress, and will move with the cursor to the drop target. This pixmap typically shows an icon that represents the MIME type of the data being transferred, but any pixmap can be set with setPixmap(). The cursor's hot spot can be given a position relative to the top-left corner of the pixmap with the setHotSpot() function. The following code positions the pixmap so that the cursor's hot spot points to the center of its bottom edge:

drag->setHotSpot(QPoint(drag->pixmap().width()/2,

drag->pixmap().height()));

Note: On X11, the pixmap may not be able to keep up with the mouse movements if the hot spot causes the pixmap to be displayed directly under the cursor.

The source and target widgets can be found with source() and target(). These functions are often used to determine whether drag and drop operations started and finished at the same widget, so that special behavior can be implemented.

QDrag only deals with the drag and drop operation itself. It is up to the developer to decide when a drag operation begins, and how a QDrag object should be constructed and used. For a given widget, it is often necessary to reimplement mousePressEvent() to determine whether the user has pressed a mouse button, and reimplement mouseMoveEvent() to check whether a QDrag is required.

See also: {Drag and Drop}, QClipboard, QMimeData, QWindowsMime, QMacPasteboardMime, {Draggable Icons Example}, {Draggable Text Example}, {Drop Site Example}, {Fridge Magnets Example}

Definition at line 61 of file qdrag.h.

Constructors and Destructors

◆ QDrag()

QDrag::QDrag ( QWidget * dragSource )

explicit

Constructs a new drag object for the widget specified by dragSource.

Definition at line 113 of file qdrag.cpp.

     : QObject(*new QDragPrivate, dragSource)
 {
     Q_D(QDrag);
     d->source = dragSource;
     d->target = 0;
     d->data = 0;
     d->hotspot = QPoint(-10, -10);
     d->possible_actions = Qt::CopyAction;
     d->executed_action = Qt::IgnoreAction;
     d->defaultDropAction = Qt::IgnoreAction;
 }

◆ ~QDrag()

QDrag::~QDrag ( )

Destroys the drag object.

Definition at line 129 of file qdrag.cpp.

 {
     Q_D(QDrag);
     delete d->data;
     QDragManager *manager = QDragManager::self();
     if (manager && manager->object == this)
         manager->cancel(false);
 }

Functions

◆ actionChanged

void QDrag::actionChanged ( Qt::DropAction action )

signal

This signal is emitted when the action associated with the drag changes.

See also: targetChanged()

◆ exec() [1/2]

Qt::DropAction QDrag::exec ( Qt::DropActions supportedActions = Qt::MoveAction )

Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed.

Since: 4.3

The drop actions that the user can choose from are specified in supportedActions. The default proposed action will be selected among the allowed actions in the following order: Move, Copy and Link.

Note: On Linux and Mac OS X, the drag and drop operation can take some time, but this function does not block the event loop. Other events are still delivered to the application while the operation is performed. On Windows, the Qt event loop is blocked while during the operation.

Definition at line 243 of file qdrag.cpp.

Referenced by QIconModeViewBase::filterStartDrag(), QmlJSDebugger::ToolBarColorBox::mouseMoveEvent(), QTextControlPrivate::startDrag(), and QAbstractItemView::startDrag().

 {
     return exec(supportedActions, Qt::IgnoreAction);
 }

◆ exec() [2/2]

Qt::DropAction QDrag::exec	(	Qt::DropActions	supportedActions,
		Qt::DropAction	defaultDropAction
	)

Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed.

Since: 4.3

The drop actions that the user can choose from are specified in supportedActions.

The defaultDropAction determines which action will be proposed when the user performs a drag without using modifier keys.

Note: On Linux and Mac OS X, the drag and drop operation can take some time, but this function does not block the event loop. Other events are still delivered to the application while the operation is performed. On Windows, the Qt event loop is blocked during the operation. However, QDrag::exec() on Windows causes processEvents() to be called frequently to keep the GUI responsive. If any loops or operations are called while a drag operation is active, it will block the drag operation.

Definition at line 270 of file qdrag.cpp.

 {
     Q_D(QDrag);
     if (!d->data) {
         qWarning("QDrag: No mimedata set before starting the drag");
         return d->executed_action;
     }
     QDragManager *manager = QDragManager::self();
     d->defaultDropAction = Qt::IgnoreAction;
     d->possible_actions = supportedActions;
 
     if (manager) {
         if (defaultDropAction == Qt::IgnoreAction) {
             if (supportedActions & Qt::MoveAction) {
                 d->defaultDropAction = Qt::MoveAction;
             } else if (supportedActions & Qt::CopyAction) {
                 d->defaultDropAction = Qt::CopyAction;
             } else if (supportedActions & Qt::LinkAction) {
                 d->defaultDropAction = Qt::LinkAction;
             }
         } else {
             d->defaultDropAction = defaultDropAction;
         }
         d->executed_action = manager->drag(this);
     }
 
     return d->executed_action;
 }

◆ hotSpot()

QPoint QDrag::hotSpot ( ) const

Returns the position of the hot spot relative to the top-left corner of the cursor.

Definition at line 199 of file qdrag.cpp.

Referenced by QOleDropSource::createCursors().

 {
     Q_D(const QDrag);
     return d->hotspot;
 }

◆ mimeData()

QMimeData * QDrag::mimeData ( ) const

Returns the MIME data that is encapsulated by the drag object.

Definition at line 155 of file qdrag.cpp.

Referenced by QDragManager::drag(), and QOleDropTarget::Drop().

 {
     Q_D(const QDrag);
     return d->data;
 }

◆ pixmap()

QPixmap QDrag::pixmap ( ) const

Returns the pixmap used to represent the data in a drag and drop operation.

Definition at line 175 of file qdrag.cpp.

Referenced by QOleDropSource::createCursors(), and setPixmap().

 {
     Q_D(const QDrag);
     return d->pixmap;
 }

◆ setDragCursor()

void QDrag::setDragCursor	(	const QPixmap &	cursor,
		Qt::DropAction	action
	)

Sets the drag cursor for the action.

This allows you to override the default native cursors. To revert to using the native cursor for action pass in a null QPixmap as cursor.

The action can only be CopyAction, MoveAction or LinkAction. All other values of DropAction are ignored.

Definition at line 340 of file qdrag.cpp.

 {
     Q_D(QDrag);
     if (action != Qt::CopyAction && action != Qt::MoveAction && action != Qt::LinkAction)
         return;
     if (cursor.isNull())
         d->customCursors.remove(action);
     else
         d->customCursors[action] = cursor;
 }

◆ setHotSpot()

void QDrag::setHotSpot ( const QPoint & hotspot )

Sets the position of the hot spot relative to the top-left corner of the pixmap used to the point specified by hotspot.

Note: on X11, the pixmap may not be able to keep up with the mouse movements if the hot spot causes the pixmap to be displayed directly under the cursor.

Definition at line 189 of file qdrag.cpp.

Referenced by QIconModeViewBase::filterStartDrag(), and QAbstractItemView::startDrag().

 {
     Q_D(QDrag);
     d->hotspot = hotspot;
 }

◆ setMimeData()

void QDrag::setMimeData ( QMimeData * data )

Sets the data to be sent to the given MIME data.

Ownership of the data is transferred to the QDrag object.

Definition at line 142 of file qdrag.cpp.

Referenced by QLineEditPrivate::drag(), QDragManager::drag(), QOleDropTarget::Drop(), QIconModeViewBase::filterStartDrag(), QmlJSDebugger::ToolBarColorBox::mouseMoveEvent(), QColorWell::mouseMoveEvent(), QColorShowLabel::mouseMoveEvent(), QTextControlPrivate::startDrag(), and QAbstractItemView::startDrag().

 {
     Q_D(QDrag);
     if (d->data == data)
         return;
     if (d->data != 0)
         delete d->data;
     d->data = data;
 }

◆ setPixmap()

void QDrag::setPixmap ( const QPixmap & pixmap )

Sets pixmap as the pixmap used to represent the data in a drag and drop operation.

You can only set a pixmap before the drag is started.

Definition at line 166 of file qdrag.cpp.

Referenced by QIconModeViewBase::filterStartDrag(), QmlJSDebugger::ToolBarColorBox::mouseMoveEvent(), QColorWell::mouseMoveEvent(), QColorShowLabel::mouseMoveEvent(), and QAbstractItemView::startDrag().

 {
     Q_D(QDrag);
     d->pixmap = pixmap;
 }

◆ source()

QWidget * QDrag::source ( ) const

Returns the source of the drag object.

This is the widget where the drag and drop operation originated.

Definition at line 209 of file qdrag.cpp.

Referenced by QX11Data::dndEnable(), and QOleDropTarget::Drop().

 {
     Q_D(const QDrag);
     return d->source;
 }

◆ start()

Qt::DropAction QDrag::start ( Qt::DropActions request = Qt::CopyAction )

Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed.

Note: It is recommended to use exec() instead of this function.

The drop actions that the user can choose from are specified in request. Qt::CopyAction is always allowed.

Note: Although the drag and drop operation can take some time, this function does not block the event loop. Other events are still delivered to the application while the operation is performed.

See also: exec()

Definition at line 317 of file qdrag.cpp.

Referenced by QLineEditPrivate::drag(), QColorWell::mouseMoveEvent(), and QColorShowLabel::mouseMoveEvent().

 {
     Q_D(QDrag);
     if (!d->data) {
         qWarning("QDrag: No mimedata set before starting the drag");
         return d->executed_action;
     }
     QDragManager *manager = QDragManager::self();
     d->defaultDropAction = Qt::IgnoreAction;
     d->possible_actions = request | Qt::CopyAction;
     if (manager)
         d->executed_action = manager->drag(this);
     return d->executed_action;
 }

◆ target()

QWidget * QDrag::target ( ) const

Returns the target of the drag and drop operation.

This is the widget where the drag object was dropped.

Definition at line 219 of file qdrag.cpp.

Referenced by QX11Data::dndEnable(), QLineEditPrivate::drag(), QDragManager::drag(), and QTextControlPrivate::startDrag().

 {
     Q_D(const QDrag);
     return d->target;
 }

◆ targetChanged

void QDrag::targetChanged ( QWidget * newTarget )

signal

This signal is emitted when the target of the drag and drop operation changes, with newTarget the new target.

See also: target(), actionChanged()

Friends and Related Functions

◆ QDragManager

friend class QDragManager

friend

Definition at line 95 of file qdrag.h.

◆ QWidgetPrivate

friend class QWidgetPrivate

friend

Definition at line 93 of file qdrag.h.

The documentation for this class was generated from the following files:

/src/gui/kernel/qdrag.h
/src/gui/kernel/qdrag.cpp

Signals

Public Functions

Friends

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ QDrag()

◆ ~QDrag()

Functions

◆ actionChanged

◆ exec() [1/2]

◆ exec() [2/2]

◆ hotSpot()

◆ mimeData()

◆ pixmap()

◆ setDragCursor()

◆ setHotSpot()

◆ setMimeData()

◆ setPixmap()

◆ source()

◆ start()

◆ target()

◆ targetChanged

Friends and Related Functions

◆ QDragManager

◆ QWidgetPrivate