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    41 

    42 /*!

    43     \example draganddrop/draggableicons

    44     \title Draggable Icons Example

    45 

    46     The Draggable Icons example shows how to drag and drop image data between widgets

    47     in the same application, and between different applications.

    48 

    49     \image draggableicons-example.png

    50 

    51     In many situations where drag and drop is used, the user starts dragging from

    52     a particular widget and drops the payload onto another widget. In this example,

    53     we subclass QLabel to create labels that we use as drag sources, and place them

    54     inside \l{QWidget}s that serve as both containers and drop sites.

    55 

    56     In addition, when a drag and drop operation occurs, we want to send more than

    57     just an image. We also want to send information about where the user clicked in

    58     the image so that the user can place it precisely on the drop target. This level

    59     of detail means that we must create a custom MIME type for our data.

    60 

    61     \section1 DragWidget Class Definition

    62 

    63     The icon widgets that we use to display icons are subclassed from QLabel:

    64 

    65     \snippet examples/draganddrop/draggableicons/dragwidget.h 0

    66 

    67     Since the QLabel class provides most of what we require for the icon, we

    68     only need to reimplement the \l QWidget::mousePressEvent() to provide

    69     drag and drop facilities.

    70 

    71     \section1 DragWidget Class Implementation

    72 

    73     The \c DragWidget constructor sets an attribute on the widget that ensures

    74     that it will be deleted when it is closed:

    75 

    76     \snippet examples/draganddrop/draggableicons/dragwidget.cpp 0

    77 

    78     To enable dragging from the icon, we need to act on a mouse press event.

    79     We do this by reimplementing \l QWidget::mousePressEvent() and setting up

    80     a QDrag object.

    81 

    82     \snippet examples/draganddrop/draggableicons/dragwidget.cpp 1

    83 

    84     Since we will be sending pixmap data for the icon and information about the

    85     user's click in the icon widget, we construct a QByteArray and package up the

    86     details using a QDataStream.

    87 

    88     For interoperability, drag and drop operations describe the data they contain

    89     using MIME types. In Qt, we describe this data using a QMimeData object:

    90 

    91     \snippet examples/draganddrop/draggableicons/dragwidget.cpp 2

    92 

    93     We choose an unofficial MIME type for this purpose, and supply the QByteArray

    94     to the MIME data object.

    95 

    96     The drag and drop operation itself is handled by a QDrag object:

    97 

    98     \snippet examples/draganddrop/draggableicons/dragwidget.cpp 3

    99 

   100     Here, we pass the data to the drag object, set a pixmap that will be shown

   101     alongside the cursor during the operation, and define the position of a hot

   102     spot that places the position of this pixmap under the cursor.

   103 

   104 */