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Thread: QGraphicsView, QGraphicsScene and QGraphicsItem Problem :(

  1. 25th October 2011, 13:01 #1
    nudels
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    Unhappy QGraphicsView, QGraphicsScene and QGraphicsItem Problem :(

    Hello Guys

    Im very new in Qt and have a little Problem, maybe its not a Qt Problem or a thinking error.

    Okay lets start
    I want to build a GUI that have a modular window architecture. I thought i create a QMainWindow and set a QGraphicsView as the centralWidget.
    Now i create a MainScene and set it up to the View and in this Scene i have some buttons (QObejct and QGraphicsItem inherited).
    When i click e.g. "ServiceButton" then i emit a Signal from the button to the scene and from the scene to the View.
    Now i want to set a new Scene to the View, but first delete the old scene.

    At this point my program crashes :/

    i hope somebody understands me

    But my Problem is, that i don't know if this idear 100% would be work.

    Here is my Hole Code:

    Main.cpp:
    Qt Code: 
    1. #include <QtGui/QApplication>
    2. #include "mainview.h"
    3.  
    4. int main(int argc, char *argv[])
    5. {
    6.     QApplication a(argc, argv);
    7.  
    8.     QMainWindow* wMain = new QMainWindow();
    9.     MainView* mainView = new MainView();
    10.     wMain->setWindowFlags(Qt::FramelessWindowHint);
    11.     wMain->setCentralWidget(mainView);
    12.     wMain->show();
    13.  
    14.     return a.exec();
    15. }
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    MainView.cpp + .h:
    Qt Code: 
    1. #ifndef MAINVIEW_H
    2. #define MAINVIEW_H
    3.  
    4. #include <QGraphicsView>
    5. #include "mainscene.h"
    6. #include "basicscene.h"
    7.  
    8. class MainView : public QGraphicsView
    9. {
    10.     Q_OBJECT
    11. public:
    12.  
    13.     MainView(QWidget* parent = 0);
    14.     ~MainView();
    15.  
    16. protected:
    17.     void resizeEvent(QResizeEvent *event);
    18.  
    19. public slots:
    20.     void createBasicScene();
    21.     void createMainScene();
    22.  
    23. private:
    24.     MainScene* m_mainScene;
    25.     BasicScene* m_basicScene;
    26.  
    27. };
    28.  
    29. #endif // MAINVIEW_H
    30.  
    31.  
    32. #include "mainview.h"
    33. #include <QDebug>
    34. #include <QMouseEvent>
    35. #include <QtOpenGL/QtOpenGL>
    36.  
    37.  
    38. MainView::MainView(QWidget* parent) : QGraphicsView(parent)
    39. {
    40.  
    41.     qDebug() << "Start GraphicsView";
    42.     setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    43.     setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    44.     setGeometry(QRect(0,0,800,480));
    45.  
    46.     m_mainScene = new MainScene();
    47.     m_mainScene->setSceneRect(QRectF(rect()));
    48.  
    49.     setScene(m_mainScene);
    50.     setRenderHint(QPainter::Antialiasing);
    51.     setViewport(new QGLWidget());
    52.  
    53.     connect(m_mainScene, SIGNAL(setBasicScene()), this, SLOT(createBasicScene()));
    54.  
    55. }
    56.  
    57. MainView::~MainView()
    58. {
    59.     delete m_mainScene;
    60.     delete m_basicScene;
    61. }
    62.  
    63. void MainView::resizeEvent(QResizeEvent *event)
    64. {
    65.     QGraphicsView::resizeEvent(event);
    66. }
    67.  
    68.  
    69. void MainView::createBasicScene()
    70. {
    71.     if(scene() != NULL)
    72.         delete scene();
    73.     m_basicScene = new BasicScene();
    74.     setScene(m_basicScene);
    75.     connect(m_basicScene, SIGNAL(setMainScene()), this, SLOT(createMainScene()));
    76. }
    77.  
    78. void MainView::createMainScene()
    79. {
    80.     if(scene() != NULL)
    81.         delete scene();
    82.     m_mainScene = new MainScene();
    83.     setScene(m_mainScene);
    84.     connect(m_mainScene, SIGNAL(setBasicScene()), this, SLOT(createBasicScene()));
    85. }
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    MainScene.cpp + .h:
    Qt Code: 
    1. #ifndef MAINSCENE_H
    2. #define MAINSCENE_H
    3.  
    4. #include <QGraphicsScene>
    5. #include <QDebug>
    6. #include "roundrectitem.h"
    7. #include <QGraphicsSceneMouseEvent>
    8.  
    9. class MainScene : public QGraphicsScene
    10. {
    11.     Q_OBJECT
    12. public:
    13.     MainScene(QObject* parent = 0);
    14.     ~MainScene();
    15.  
    16. protected:
    17.     void mousePressEvent(QGraphicsSceneMouseEvent *event);
    18.  
    19.  
    20. public slots:
    21.     void buttonService();
    22.  
    23. signals:
    24.     void setBasicScene();
    25.  
    26. private:
    27.     RoundRectItem* rect;
    28. //    RoundRectItem* rect2;
    29. //    RoundRectItem* rect3;
    30.  
    31. };
    32.  
    33. #endif // MAINSCENE_H
    34.  
    35. #include "mainscene.h"
    36.  
    37.  
    38. MainScene::MainScene(QObject* parent) : QGraphicsScene(parent)
    39. {
    40.     setSceneRect(0,0,800,480);
    41.     qDebug() << "Start MainScene";
    42.     QRectF iconRect(-100, -100, 200, 200);
    43.     QColor iconColor(214,240,110,128);
    44.     rect = new RoundRectItem(iconRect, iconColor);
    45.  
    46.     rect->setObjectName("button");
    47.  
    48.     addItem(rect);
    49.  
    50.     rect->setPos(100,100);
    51.  
    52.     connect(rect, SIGNAL(clicked()), this, SLOT(buttonService()));
    53. }
    54.  
    55. MainScene::~MainScene()
    56. {
    57.     //removeItem(rect);
    58.     clear();
    59. }
    60.  
    61. void MainScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
    62. {
    63.  
    64.     QGraphicsScene::mousePressEvent(event);
    65.     qDebug() << "MainScene: Pressed";
    66. //    RoundRectItem* child = qgraphicsitem_cast<RoundRectItem*>( itemAt(event->scenePos()));
    67.     //    if(!child)
    68.     //        return;
    69.  
    70. }
    71.  
    72.  
    73. void MainScene::buttonService()
    74. {
    75.     emit setBasicScene();
    76. }
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    RoundRectItem.cpp + .h:
    Qt Code: 
    1. #ifndef ROUNDRECTITEM_H
    2. #define ROUNDRECTITEM_H
    3.  
    4. #include <QGraphicsObject>
    5. #include <QLinearGradient>
    6. #include <QGraphicsDropShadowEffect>
    7. #include <QPropertyAnimation>
    8. #include <QGraphicsRotation>
    9. #include <QGraphicsItem>
    10. #include <QObject>
    11.  
    12. class RoundRectItem :  public QObject, public QGraphicsItem
    13. {
    14.     Q_OBJECT
    15.     Q_PROPERTY(bool fill READ fill WRITE setFill)
    16. public:
    17.     RoundRectItem(const QRectF bounds, const QColor &color);
    18.     ~RoundRectItem();
    19.     QPixmap pixmap()const;
    20.     void setPixmap(const QPixmap &pixmap);
    21.  
    22.     QRectF boundingRect() const;
    23.     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    24.  
    25.     bool fill()const;
    26.     void setFill(bool fill);
    27.  
    28.     QString objectName() const;
    29.     void setObjectName(const QString &name);
    30.  
    31. protected:
    32.     void mousePressEvent(QGraphicsSceneMouseEvent *event);
    33.  
    34. signals:
    35.     void clicked();
    36.  
    37.  
    38.  
    39. private:
    40.     QPixmap pix;
    41.     bool fillRect;
    42.     QRectF bounds;
    43.     QLinearGradient gradient;
    44.     QGraphicsDropShadowEffect* shadow;
    45.     QString m_objectName;
    46.  
    47.  
    48. };
    49.  
    50. #endif // ROUNDRECTITEM_H
    51.  
    52. #include "roundrectitem.h"
    53. #include <QtGui>
    54. #include <QDebug>
    55. #include <QPainterPath>
    56.  
    57. RoundRectItem::RoundRectItem(const QRectF bounds, const QColor &color)
    58.     :  QObject(0), QGraphicsItem(), fillRect(false), bounds(bounds)
    59. {
    60.     gradient.setStart(bounds.topLeft());
    61.     gradient.setFinalStop(bounds.bottomRight());
    62.     gradient.setColorAt(0, color);
    63.     gradient.setColorAt(1, color.dark(200));
    64.     setCacheMode(ItemCoordinateCache);
    65.  
    66.     shadow = new QGraphicsDropShadowEffect();
    67.     shadow->setBlurRadius(50);
    68.     shadow->setColor(QColor(0x40,0x40,0x40,255));
    69.     setGraphicsEffect(shadow);
    70.  
    71.     m_objectName = "x";
    72.  
    73. }
    74.  
    75. RoundRectItem::~RoundRectItem()
    76. {
    77.     delete shadow;
    78. }
    79.  
    80.  
    81. QPixmap RoundRectItem::pixmap()const
    82. {
    83.     return pix;
    84. }
    85.  
    86. void RoundRectItem::setPixmap(const QPixmap &pixmap)
    87. {
    88.     pix = pixmap;
    89.  
    90.     setFlags(flags() | QGraphicsItem::ItemIsSelectable);
    91.     update();
    92. }
    93.  
    94. void RoundRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    95. {
    96.     Q_UNUSED(option);
    97.     Q_UNUSED(widget);
    98.     painter->setPen(Qt::NoPen);
    99.     painter->setBrush(QColor(0,0,0,64));
    100.     painter->drawRoundRect(bounds.translated(2,2));
    101.    // painter->drawRoundRect(bounds);
    102.  
    103.     if(fillRect)
    104.         painter->setBrush(QApplication::palette().brush(QPalette::Window));
    105.     else
    106.         painter->setBrush(gradient);
    107.     painter->setPen(QPen(Qt::black,1));
    108.     painter->drawRoundRect(bounds);
    109.  
    110.     if(!pix.isNull())
    111.     {
    112.         painter->scale(1.95,1.95);
    113.         painter->drawPixmap(-pix.width() /2, -pix.height()/2, pix);
    114.     }
    115.     else{
    116.  
    117.         QPainterPath* path = new QPainterPath();
    118.         QFont serifFont("Times", 20, QFont::Bold);
    119.         path->addText(bounds.center().x(),bounds.center().y(), serifFont, m_objectName);
    120.         painter->drawPath(*path);
    121.     }
    122. }
    123.  
    124. bool RoundRectItem::fill() const
    125. {
    126.     return fillRect;
    127. }
    128.  
    129.  
    130. void RoundRectItem::setFill(bool fill)
    131. {
    132.     fillRect = fill;
    133.     update();
    134. }
    135.  
    136. QString RoundRectItem::objectName() const
    137. {
    138.     return m_objectName;
    139. }
    140.  
    141. void RoundRectItem::setObjectName(const QString &name)
    142. {
    143.     m_objectName = name;
    144. }
    145.  
    146. QRectF RoundRectItem::boundingRect()const
    147. {
    148.     return bounds.adjusted(0,0,2,2);
    149. }
    150.  
    151. void RoundRectItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
    152. {
    153.  
    154.    // QGraphicsItem::mousePressEvent(event);
    155.     qDebug() << "RoundRectItem: Pressed";
    156.     emit clicked();
    157.  
    158. }
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    The BasicScene is just Similar to MainScene.

    Or can i made my idear in another way to change the scene's or Views?

    Thank for Help

    Best regards

    nudels
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  2. 25th October 2011, 14:17 #2
    dennis81
    dennis81 is offline Novice
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    Default Re: QGraphicsView, QGraphicsScene and QGraphicsItem Problem :(

    so vielleicht?

    Qt Code: 
    1. connect(m_mainScene, SIGNAL(setBasicScene()), this, SLOT(createBasicScene()), Qt:QueedConnection);
    2.  
    3.  
    4.  
    5. if(scene() != NULL)
    6. m_basicScene->deleteLater();
    7. m_basicScene = new BasicScene();
    8. setScene(m_basicScene);
    9. connect(m_basicScene, SIGNAL(setMainScene()), this, SLOT(createMainScene()));
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  3. 26th October 2011, 10:41 #3
    nudels
    nudels is offline Beginner
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    Default Re: QGraphicsView, QGraphicsScene and QGraphicsItem Problem :(

    Hey dennis81,

    thanks for ur reply

    now i have solced my problem and get a new one
    when i click on my scene then i get a debug output: "MainScene: Pressed". thats all right, but when i click now on a roundrectitem in the scene, then i get this output:
    "RoundRectItem: Pressed
    MainScene: Pressed"

    but i dont want that the scene gets an MousePressEvent, because i just want to "press" the RoundRectItem.
    How can i made this? do i need an eventFilter in the Scene?

    And another question i have:
    Is it better, when i make my own SceneItems like RoundRectitem, to inherit from QGraphicsItem or QGraphicsObject?

    I ask, because when i inherit from QGraphicsItem and QObject and want to Animate like move in x-direction, then i need to create a new Q_PROPERTY. But when i inherit from QGraphicsObejct, then i have more defined Propertys, which i can animate.

    Thanks for helping

    with best regards

    nudels
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  4. 26th October 2011, 11:01 #4
    stampede
    stampede is offline Expert
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    Default Re: QGraphicsView, QGraphicsScene and QGraphicsItem Problem :(

    How can i made this? do i need an eventFilter in the Scene?
    You can call event->accept() in rect item, and test if event->isAccepted() in scene mousePressEvent.
    About your second question, I think you answered it yourself - if inheriting from QGraphicsItem requires you to do more work, isn't it better to use QGraphicsObject ?
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  5. The following user says thank you to stampede for this useful post:

    nudels (26th October 2011)
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