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  1. 23rd June 2010, 10:47 #1
    mrothe
    mrothe is offline Beginner
    Join Date
    Jun 2010
    Posts
    3

    Question QGraphicsView move item issues.

    Hello,

    I am new to deveopment with Qt and are currently developing a simple application which let's you create graphical representation of a scene (e.g. a room) with a transmitter and several sensors. I use the QGraphics framework for this task. The "scene edge" is represented by a class derived from QGraphicsRectItem. The transmitter class is derived from QGraphicsEllipseItem and the sensors are derived from QGraphicsPolygonItem. All these objects and the QGraphicsView/QGraphicsScene are part of the UIInputSceneWidget.

    I was at a point where I was able to move items separately. I.e. the item under the mouse cursor was moved, when you click, hold and move. But now that I moved a few functions around it doesn't work any more and I cannot figure out why.

    There are two possibilities what happens:

    1. If I move the scene edge (QGraphicsRectItem) before adding the transmitter or the sensors, then this rectangle is moved wherever I click, hold and move in the QGraphicsView. The rectangle "jumps" under the cursor as soon as I move the mouse. Even if I click outside the rectangle this happens.

    2. If I do not move the rectangle before adding the transmitter or the sensors, then I can only move the first item that I added (either the transmitter or the first sensor). This item also "jumps" under the cursor as soon as I click, hold and move on a point in the view.

    Here is the code that I suppose is relevant. Please ask for more if this is not sufficient:

    Qt Code: 
    1. class UIInputSceneWidget : public QWidget
    2. {
    3.     Q_OBJECT
    4.  
    5.     public:
    6.         [...]
    7.     signals:
    8.         [...]
    9.     private slots:
    10.         void insertFinished();
    11.         void insertSceneEdge(UISceneEdge *newSceneEdge);
    12.         void insertSensor(QGraphicsSceneMouseEvent *mouseEvent);
    13.         void insertTransmitter(QGraphicsSceneMouseEvent *mouseEvent);
    14.         [...]
    15.  
    16.     private:
    17.         UIGraphicsScene *scene;
    18.         UIGraphicsView *view;
    19.  
    20.         UISceneEdge *sceneEdge;
    21.         UITransmitter *transmitter;
    22.         QVector<UISensor *> sensors;
    23.         [...]
    24. };
    25.  
    26. void UIInputSceneWidget::insertFinished()
    27. {
    28.     if (scene->getMode() == UIGraphicsScene::InsertEdge)
    29.         scene->setMode(UIGraphicsScene::MoveItem);
    30. }
    31.  
    32. void UIInputSceneWidget::insertSceneEdge(UISceneEdge *newSceneEdge)
    33. {
    34.     if (sceneEdge == NULL) {
    35.         sceneEdge = newSceneEdge;
    36.     } else {
    37.         delete newSceneEdge;
    38.         return;
    39.     }
    40.     // stuff regarding buttons which is not important here
    41. }
    42.  
    43. void UIInputSceneWidget::insertSensor(QGraphicsSceneMouseEvent *mouseEvent)
    44. {
    45.     if ((sceneEdge == NULL) || !(sceneEdge->pointIsInsideSceneEdge(mouseEvent->scenePos())))
    46.         return;
    47.  
    48.     UISensor *newSensor = new UISensor(mouseEvent->scenePos(), sceneEdge);
    49.     sensors.push_back(newSensor);
    50.  
    51.     QString str;
    52.     str.setNum(sensors.size());
    53.     sensorLineEdit->setText(str);
    54. }
    55.  
    56. void UIInputSceneWidget::insertTransmitter(QGraphicsSceneMouseEvent *mouseEvent)
    57. {
    58.     if ((sceneEdge == NULL) || !(sceneEdge->pointIsInsideSceneEdge(mouseEvent->scenePos())))
    59.         return;
    60.  
    61.     UITransmitter *newTransmitter = new UITransmitter(mouseEvent->scenePos(), sceneEdge);
    62.     transmitter = newTransmitter;
    63.  
    64.     transmitterButton->setChecked(false);
    65.     transmitterButton->setEnabled(false);
    66.     scene->setMode(UIGraphicsScene::MoveItem);
    67.     setTransmitterLocationLabel();
    68. }
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    Qt Code: 
    1. class UIGraphicsScene : public QGraphicsScene
    2. {
    3.     Q_OBJECT
    4.  
    5.     public:
    6.         enum Mode { InsertEdge, InsertTransmitter, InsertSensor, MoveItem };
    7.         void setMode(Mode mode);
    8.         [...]
    9.  
    10.     signals:
    11.         void insertFinished();
    12.         void insertSceneEdge(UISceneEdge *sceneEdge);
    13.         void insertSensor(QGraphicsSceneMouseEvent *mouseEvent);
    14.         void insertTransmitter(QGraphicsSceneMouseEvent *mouseEvent);
    15.         [...]
    16.  
    17.     protected:
    18.         void drawBackground(QPainter *painter, const QRectF &rect);
    19.         void mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent);
    20.         void mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent);
    21.         void mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent);
    22.  
    23.     private:
    24.         Mode myMode;
    25.         QPointF firstPointOfSceneEdge;
    26. };
    27.  
    28. void UIGraphicsScene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
    29. {
    30.     if (myMode == InsertEdge) {
    31.         qreal x1 = firstPointOfSceneEdge.x();
    32.         qreal x2 = mouseEvent->scenePos().x();
    33.         qreal y1 = firstPointOfSceneEdge.y();
    34.         qreal y2 = mouseEvent->scenePos().y();
    35.         QPointF topLeft;
    36.         QPointF bottomRight;
    37.  
    38.         if (x1 < x2) {
    39.             topLeft.setX(x1);
    40.             bottomRight.setX(x2);
    41.         } else {
    42.             topLeft.setX(x2);
    43.             bottomRight.setX(x1);
    44.         }
    45.  
    46.         if (y1 < y2) {
    47.             topLeft.setY(y1);
    48.             bottomRight.setY(y2);
    49.         } else {
    50.             topLeft.setY(y2);
    51.             bottomRight.setY(y1);
    52.         }
    53.  
    54.         emit setSceneSize(QRectF(topLeft, bottomRight));
    55.     } else if (myMode == MoveItem) {
    56.         QGraphicsScene::mouseMoveEvent(mouseEvent);
    57.         emit moveEvent(); /* for updating labels and stuff */
    58.     }
    59. }
    60.  
    61. void UIGraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
    62. {
    63.     if (mouseEvent->button() != Qt::LeftButton)
    64.         return;
    65.  
    66.     switch (myMode) {
    67.     case InsertEdge: {
    68.         firstPointOfSceneEdge = mouseEvent->scenePos();
    69.         UISceneEdge *sceneEdge = new UISceneEdge(QRectF(firstPointOfSceneEdge,
    70.                                                         firstPointOfSceneEdge));
    71.         addItem(sceneEdge);
    72.         emit insertSceneEdge(sceneEdge);
    73.         emit setSceneSize(QRectF(firstPointOfSceneEdge,
    74.                                  firstPointOfSceneEdge));
    75.         break;
    76.     }
    77.     case InsertSensor: {
    78.         /* The sensor cannot be inserted directly because the pointer to
    79.          * the sceneEdge is not stored in this object, but in
    80.          * UIInputWidget. Let that object create and add the sensor. */
    81.         emit insertSensor(mouseEvent);
    82.         break;
    83.     }
    84.     case InsertTransmitter: {
    85.         /* Same reason as above! */
    86.         emit insertTransmitter(mouseEvent);
    87.         break;
    88.     }
    89.     default:
    90.         ;
    91.     }
    92.     QGraphicsScene::mousePressEvent(mouseEvent);
    93. }
    94.  
    95. void UIGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
    96. {
    97.     emit insertFinished();
    98. }
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    UIGraphicsView is derived from QGraphicsView and just reimplements keyPressEvent(), wheelEvent() and scaleView(). Nothing special there...

    A screenshot showing the application is attached. This might help you understand the situation.

    I really don't know what happens... Please help me.

    Regards,

    Markus

    EDIT: It might not be clear enough what I want: I want that the item under the mouse cursor moves. If it is the transmitter, then the transmitter should move. If it is a sensor then the sensor should move. If the rectangle is below the cursor then, the rectangle and it's children should move.
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