com.trolltech.qt.gui
Class QDrag

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QObject
                  extended by com.trolltech.qt.gui.QDrag
All Implemented Interfaces:
QtJambiInterface

public class QDrag
extends QObject

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(new 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, and Fridge Magnets Example.


Nested Class Summary
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 QSignalEmitter.Signal1 actionChanged
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal1 targetChanged
          This signal takes 1 generic argument(s).
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QDrag(QWidget dragSource)
          Constructs a new drag object for the widget specified by dragSource.
 
Method Summary
 Qt.DropAction exec()
          Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed.
 Qt.DropAction exec(Qt.DropAction[] supportedActions)
          This is an overloaded method provided for convenience.
 Qt.DropAction exec(Qt.DropActions supportedActions)
          Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed.
 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.
 QPoint hotSpot()
          Returns the position of the hot spot relative to the top-left corner of the cursor.
 QMimeData mimeData()
          Returns the MIME data that is encapsulated by the drag object.
 QPixmap pixmap()
          Returns the pixmap used to represent the data in a drag and drop operation.
 void setDragCursor(QPixmap cursor, Qt.DropAction action)
          Sets the drag cursor for the action.
 void setHotSpot(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.
 void setMimeData(QMimeData data)
          Sets the data to be sent to the given MIME data.
 void setPixmap(QPixmap arg__1)
          Sets pixmap as the pixmap used to represent the data in a drag and drop operation.
 QWidget source()
          Returns the source of the drag object.
 QWidget target()
          Returns the target of the drag and drop operation.
 
Methods inherited from class com.trolltech.qt.core.QObject
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Field Detail

actionChanged

public final QSignalEmitter.Signal1 actionChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <com.trolltech.qt.core.Qt$DropAction(named: action)>:

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

See also:
targetChanged() .


targetChanged

public final QSignalEmitter.Signal1 targetChanged

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <com.trolltech.qt.gui.QWidget(named: newTarget)>:

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

See also:
target(), and actionChanged() .

Constructor Detail

QDrag

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

Method Detail

exec

public final Qt.DropAction exec(Qt.DropAction[] supportedActions)
This is an overloaded method provided for convenience.


exec

public final Qt.DropAction exec()
Starts the drag and drop operation and returns a value indicating the requested drop action when it is completed. 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.


exec

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


exec

public final 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. 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 while during the operation.


hotSpot

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

See also:
setHotSpot().


mimeData

public final QMimeData mimeData()
Returns the MIME data that is encapsulated by the drag object.

See also:
setMimeData().


pixmap

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

See also:
setPixmap().


setDragCursor

public final void setDragCursor(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.


setHotSpot

public final void setHotSpot(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.

See also:
hotSpot().


setMimeData

public final void setMimeData(QMimeData data)
Sets the data to be sent to the given MIME data. Ownership of the data is transferred to the QDrag object.

See also:
mimeData().


setPixmap

public final void setPixmap(QPixmap arg__1)
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.

See also:
pixmap().


source

public final QWidget source()
Returns the source of the drag object. This is the widget where the drag and drop operation originated.


target

public final QWidget target()
Returns the target of the drag and drop operation. This is the widget where the drag object was dropped.