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diagramscene.cpp Example File
graphicsview/diagramscene/diagramscene.cpp

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 #include <QtGui>

 #include "diagramscene.h"
 #include "arrow.h"

 DiagramScene::DiagramScene(QMenu *itemMenu, QObject *parent)
     : QGraphicsScene(parent)
 {
     myItemMenu = itemMenu;
     myMode = MoveItem;
     myItemType = DiagramItem::Step;
     line = 0;
     textItem = 0;
     myItemColor = Qt::white;
     myTextColor = Qt::black;
     myLineColor = Qt::black;
 }

 void DiagramScene::setLineColor(const QColor &color)
 {
     myLineColor = color;
     if (isItemChange(Arrow::Type)) {
         Arrow *item =
             qgraphicsitem_cast<Arrow *>(selectedItems().first());
         item->setColor(myLineColor);
         update();
     }
 }

 void DiagramScene::setTextColor(const QColor &color)
 {
     myTextColor = color;
     if (isItemChange(DiagramTextItem::Type)) {
         DiagramTextItem *item =
             qgraphicsitem_cast<DiagramTextItem *>(selectedItems().first());
         item->setDefaultTextColor(myTextColor);
     }
 }

 void DiagramScene::setItemColor(const QColor &color)
 {
     myItemColor = color;
     if (isItemChange(DiagramItem::Type)) {
         DiagramItem *item =
             qgraphicsitem_cast<DiagramItem *>(selectedItems().first());
         item->setBrush(myItemColor);
     }
 }

 void DiagramScene::setFont(const QFont &font)
 {
     myFont = font;

     if (isItemChange(DiagramTextItem::Type)) {
         QGraphicsTextItem *item =
             qgraphicsitem_cast<DiagramTextItem *>(selectedItems().first());
         //At this point the selection can change so the first selected item might not be a DiagramTextItem
         if (item)
             item->setFont(myFont);
     }
 }

 void DiagramScene::setMode(Mode mode)
 {
     myMode = mode;
 }

 void DiagramScene::setItemType(DiagramItem::DiagramType type)
 {
     myItemType = type;
 }

 void DiagramScene::editorLostFocus(DiagramTextItem *item)
 {
     QTextCursor cursor = item->textCursor();
     cursor.clearSelection();
     item->setTextCursor(cursor);

     if (item->toPlainText().isEmpty()) {
         removeItem(item);
         item->deleteLater();
     }
 }

 void DiagramScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (mouseEvent->button() != Qt::LeftButton)
         return;

     DiagramItem *item;
     switch (myMode) {
         case InsertItem:
             item = new DiagramItem(myItemType, myItemMenu);
             item->setBrush(myItemColor);
             addItem(item);
             item->setPos(mouseEvent->scenePos());
             emit itemInserted(item);
             break;
         case InsertLine:
             line = new QGraphicsLineItem(QLineF(mouseEvent->scenePos(),
                                         mouseEvent->scenePos()));
             line->setPen(QPen(myLineColor, 2));
             addItem(line);
             break;
         case InsertText:
             textItem = new DiagramTextItem();
             textItem->setFont(myFont);
             textItem->setTextInteractionFlags(Qt::TextEditorInteraction);
             textItem->setZValue(1000.0);
             connect(textItem, SIGNAL(lostFocus(DiagramTextItem*)),
                     this, SLOT(editorLostFocus(DiagramTextItem*)));
             connect(textItem, SIGNAL(selectedChange(QGraphicsItem*)),
                     this, SIGNAL(itemSelected(QGraphicsItem*)));
             addItem(textItem);
             textItem->setDefaultTextColor(myTextColor);
             textItem->setPos(mouseEvent->scenePos());
             emit textInserted(textItem);
     default:
         ;
     }
     QGraphicsScene::mousePressEvent(mouseEvent);
 }

 void DiagramScene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (myMode == InsertLine && line != 0) {
         QLineF newLine(line->line().p1(), mouseEvent->scenePos());
         line->setLine(newLine);
     } else if (myMode == MoveItem) {
         QGraphicsScene::mouseMoveEvent(mouseEvent);
     }
 }

 void DiagramScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (line != 0 && myMode == InsertLine) {
         QList<QGraphicsItem *> startItems = items(line->line().p1());
         if (startItems.count() && startItems.first() == line)
             startItems.removeFirst();
         QList<QGraphicsItem *> endItems = items(line->line().p2());
         if (endItems.count() && endItems.first() == line)
             endItems.removeFirst();

         removeItem(line);
         delete line;

         if (startItems.count() > 0 && endItems.count() > 0 &&
             startItems.first()->type() == DiagramItem::Type &&
             endItems.first()->type() == DiagramItem::Type &&
             startItems.first() != endItems.first()) {
             DiagramItem *startItem =
                 qgraphicsitem_cast<DiagramItem *>(startItems.first());
             DiagramItem *endItem =
                 qgraphicsitem_cast<DiagramItem *>(endItems.first());
             Arrow *arrow = new Arrow(startItem, endItem);
             arrow->setColor(myLineColor);
             startItem->addArrow(arrow);
             endItem->addArrow(arrow);
             arrow->setZValue(-1000.0);
             addItem(arrow);
             arrow->updatePosition();
         }
     }
     line = 0;
     QGraphicsScene::mouseReleaseEvent(mouseEvent);
 }

 bool DiagramScene::isItemChange(int type)
 {
     foreach (QGraphicsItem *item, selectedItems()) {
         if (item->type() == type)
             return true;
     }
     return false;
 }


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Qt 4.6.3