Qt 4.8: Q3DragObject Class Reference

Qt Reference Documentation

# Q3DragObject Class Reference

The Q3DragObject class encapsulates MIME-based data transfer. More...

     #include <Q3DragObject>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Inherits: QObject and QMimeSource.

Inherited by: Q3IconDrag, Q3ImageDrag, Q3StoredDrag, and Q3TextDrag.

- List of all members, including inherited members

## Public Types

enum | DragMode { DragDefault, DragCopy, DragMove, DragLink, DragCopyOrMove }

## Public Functions

| Q3DragObject ( QWidget * dragSource = 0, const char * name = 0 )
virtual | ~Q3DragObject ()
bool | drag ()
void | dragCopy ()
void | dragLink ()
bool | dragMove ()
QPixmap | pixmap () const
QPoint | pixmapHotSpot () const
virtual void | setPixmap ( QPixmap pm, const QPoint & hotspot )
virtual void | setPixmap ( QPixmap pm )
QWidget * | source ()

- 29 public functions inherited from QObject
- 3 public functions inherited from QMimeSource

## Static Public Members

QWidget * | target ()

- 7 static public members inherited from QObject

## Protected Functions

virtual bool | drag ( DragMode mode )

- 8 protected functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 1 signal inherited from QObject

## Detailed Description

The Q3DragObject class encapsulates MIME-based data transfer.

Q3DragObject is the base class for all data that needs to be transferred between and within applications, both for drag and drop and for the clipboard.

See the Drag and drop documentation for an overview of how to provide drag and drop in your application.

See the QClipboard documentation for an overview of how to provide cut and paste in your application.

The drag() function is used to start a drag operation. You can specify the DragMode in the call or use one of the convenience functions dragCopy(), dragMove(), or dragLink(). The drag source where the data originated is retrieved with source(). If the data was dropped on a widget within the application, target() will return a pointer to that widget. Specify the pixmap to display during the drag with setPixmap().

## Member Type Documentation

### enum Q3DragObject::DragMode

This enum describes the possible drag modes.

Constant | Value | Description
--- | --- | ---
`Q3DragObject::DragDefault` | `0` | The mode is determined heuristically.
`Q3DragObject::DragCopy` | `1` | The data is copied.
`Q3DragObject::DragMove` | `2` | The data is moved.
`Q3DragObject::DragLink` | `3` | The data is linked.
`Q3DragObject::DragCopyOrMove` | `4` | The user chooses the mode by using the Shift key to switch from the default copy mode to move mode.

## Member Function Documentation

### Q3DragObject::Q3DragObject ( QWidget * dragSource = 0, const char * name = 0 )

Constructs a drag object called name with a parent dragSource.

Note that the drag object will be deleted when the dragSource is deleted.

### Q3DragObject::~Q3DragObject ()`[virtual]`

Destroys the drag object, canceling any drag and drop operation in which it is involved.

### bool Q3DragObject::drag ()

Starts a drag operation using the contents of this object, using DragDefault mode.

The function returns true if the caller should delete the original copy of the dragged data (but see target()); otherwise returns false.

If the drag contains references to information (e.g. file names in a Q3UriDrag are references) then the return value should always be ignored, as the target is expected to directly manipulate the content referred to by the drag object. On X11 the return value should always be correct anyway, but on Windows this is not necessarily the case; e.g. the file manager starts a background process to move files, so the source must not delete the files!

Note that on Windows the drag operation will start a blocking modal event loop that will not dispatch any QTimers.

### bool Q3DragObject::drag ( DragMode mode )`[virtual protected]`

This is an overloaded function.

Starts a drag operation using the contents of this object.

At this point, the object becomes owned by Qt, not the application. You should not delete the drag object or anything it references. The actual transfer of data to the target application will be done during future event processing - after that time the drag object will be deleted.

Returns true if the dragged data was dragged as a move, indicating that the caller should remove the original source of the data (the drag object must continue to have a copy); otherwise returns false.

The mode specifies the drag mode (see Q3DragObject::DragMode.) Normally one of the simpler drag(), dragMove(), or dragCopy() functions would be used instead.

### void Q3DragObject::dragCopy ()

Starts a drag operation using the contents of this object, using `DragCopy` mode. Be sure to read the constraints described in drag().

See also drag(), dragMove(), and dragLink().

### void Q3DragObject::dragLink ()

Starts a drag operation using the contents of this object, using `DragLink` mode. Be sure to read the constraints described in drag().

See also drag(), dragCopy(), and dragMove().

### bool Q3DragObject::dragMove ()

Starts a drag operation using the contents of this object, using `DragMove` mode. Be sure to read the constraints described in drag().

Returns true if the data was dragged as a move, indicating that the caller should remove the original source of the data (the drag object must continue to have a copy); otherwise returns false.

See also drag(), dragCopy(), and dragLink().

### QPixmap Q3DragObject::pixmap () const

Returns the currently set pixmap, or a null pixmap if none is set.

See also setPixmap() and QPixmap::isNull().

### QPoint Q3DragObject::pixmapHotSpot () const

Returns the currently set pixmap hotspot.

See also setPixmap().

### void Q3DragObject::setPixmap ( QPixmap pm, const QPoint & hotspot )`[virtual]`

Set the pixmap, pm, to display while dragging the object. The platform-specific implementation will use this where it can - so provide a small masked pixmap, and do not assume that the user will actually see it.

The hotspot is the point on (or off) the pixmap that should be under the cursor as it is dragged. It is relative to the top-left pixel of the pixmap.

Warning: We have seen problems with drag cursors on different graphics hardware and driver software on Windows. Setting the graphics acceleration in the display settings down one tick solved the problems in all cases.

See also pixmap().

### void Q3DragObject::setPixmap ( QPixmap pm )`[virtual]`

This is an overloaded function.

Uses a hotspot that positions the pixmap below and to the right of the mouse pointer. This allows the user to clearly see the point on the window where they are dragging the data.

### QWidget * Q3DragObject::source ()

Returns a pointer to the widget where this object originated (the drag source).

### QWidget * Q3DragObject::target ()`[static]`

After the drag completes, this function will return the QWidget which received the drop, or 0 if the data was dropped on another application.

This can be useful for detecting the case where drag and drop is to and from the same widget.