Qt Drag and Drop

Qt drag operation is basically divided into three parts: a data acquisition (QMimeData) required for recording, the drag operation (the Drag), drop operation (the Drop);

 

QMimeData: multimedia data type, drag and drop events to pass data through the object support: text, html data, legal path, pictures, colors and so on;

 

Drag: drag and drop user an intuitive way to copy or move data in the program, which handles most of the details of the drag and drop operation

 

QDropEvent: providing a trigger event when the drag operation is completed

 

Drag and drop a picture as an example:

 

void Widget :: mousePressEvent (QMouseEvent * e) // mouse click events

{

    QLabel * child = static_cast <QLabel *> (childAt (e-> pos ())); // Gets the location of the mouse click

    if(!child)

    {

        return;

    }

QPixmap pixmap = * child-> pixmap (); // get the picture information on the control

QByteArray itemData;

QDataStream dataStream(&itemData,QIODevice::WriteOnly);

dataStream<<pixmap<<QPoint(e->pos()-child->pos());

 

QMimeData * mimeData = new QMimeData; // record data required

mimeData->setData("appDrop",itemData);

 

QDrag * drag = new QDrag (this); // create a drag and drop operation

drag-> setMimeData (mimeData); // associated data, when the drag and drop process on the data tape

pixmap=pixmap.scaled(pixmap.width()*0.1,pixmap.height()*0.1);

drag-> setPixmap (pixmap); // set when dragging the mouse to display the picture in

drag-> setHotSpot (e-> pos ()); // position, can see the note under the effect of

 

QPixmap tempPixmap=pixmap;

QPainter painter;

painter.begin(&tempPixmap);

drag-> exec (Qt :: CopyAction | Qt :: MoveAction, Qt :: CopyAction); // event that triggers a drag, you can start dragging

}

Local content will be placed onto / over the control, release the mouse to trigger the function

void Widget::dropEvent(QDropEvent *e)

{

     if (e-> mimeData () -> hasFormat ( "appDrop")) // carrying the drag operation determines whether there is data

    {Will carry out data analysis, parsing information into the original image, text, location, etc.

       QByteArray itemData=e->mimeData()->data("appDrop");

       QDataStream dataStream(&itemData,QIODevice::ReadOnly);

 

       QPixmap pixmap;

       QPoint offset;

       dataStream>>pixmap>>offset;

// display the data placement operation

       ui->label_2->setPixmap(pixmap);//前提setAcceptDrops(true);

     }

}

// mouse to drag and drop into the target control

void Widget :: wear delicate guy (QDragEnterEvent * e)

{

    if(e->mimeData()->hasFormat("appDrop"))

    {

        if(e->source()==this)

        {

            e->setDropAction(Qt::MoveAction);

            e->accept();

        }

        else{

            e->acceptProposedAction();

        }

    }else

    {

        e->ignore();

    }

}

setAcceptDrops (bool); // set the parts down whether to accept event (drop),

event-> acceptProposedAction () // drag and drop operation to the recommended operation and acceptance of the event

event-> ignore () // ignore the data, for processing data unavailable

 

enum DropAction {

        CopyAction  =  0x1 , // copy the data to the destination

        MoveAction  =  0x2 , // move data from source to target

        LinkAction  =  0x4 , // create a link from source to destination

        ActionMask  =  0xff , // no explanation

        TargetMoveAction = 0x8002,//

        IgnoreAction  =  0x0 // skip the operation (data not processed)

    };