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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"tutorial6: when and why do I have to add *parent as a class parameter and when not?","articleBody":"hi,\r\nas tp tutorial6:\r\nwhen do I have to add *parent as a class parameter and when not?\r\n\r\ne.g., not:\r\n.cpp\r\n```\r\n\r\nBullet::Bullet(): QObject(), QGraphicsRectItem(){\r\n    setRect(0,0,10,50);\r\n    QTimer * timer = new QTimer(this);\r\n    connect(timer,SIGNAL(timeout()),this,SLOT(move()));\r\n    timer-\u003estart(50);\r\n}\r\n\r\n```\r\nheader:\r\n```\r\nclass Bullet: public QObject, public QGraphicsRectItem{\r\n    Q_OBJECT\r\npublic:\r\n    Bullet(QGraphicsItem * parent=0);  // parent only in header\r\npublic slots:\r\n    void move();\r\n};\r\n\r\n```\r\n\r\n\r\n\r\nbut e.g., yes:\r\n.cpp\r\n```\r\n\r\nEnemy::Enemy(QGraphicsItem *parent): QObject(), QGraphicsRectItem(parent){ // \u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\u003c\r\n    int random_number = rand() % 700;\r\n    setPos(random_number,0);\r\n    setRect(0,0,100,100);\r\n    QTimer * timer = new QTimer(this);\r\n    connect(timer,SIGNAL(timeout()),this,SLOT(move()));\r\n    timer-\u003estart(50);\r\n}\r\n\r\n```\r\nheader:\r\n```\r\nclass Enemy: public QObject, public QGraphicsRectItem{\r\n    Q_OBJECT\r\npublic:\r\n    Enemy(QGraphicsItem * parent=0);  // parent in header like above\r\npublic slots:\r\n    void move();\r\n};\r\n\r\n```\r\n\r\ni.e., why can't I just declare \r\nEnemy::Enemy(): QObject(), QGraphicsRectItem(){ ...}[/code]`\r\n similar to  the Bullet file?\r\n\r\n(ref.: https://github.com/MeLikeyCode/QtGameTutorial/tree/master/tutorial6)\r\n\r\n(edit,  \r\nBTW, in previous tutorials https://github.com/MeLikeyCode/QtGameTutorial/tree/master/tutorial1 ... https://github.com/MeLikeyCode/QtGameTutorial/tree/master/tutorial5 this \"parents\" thing has not been added at all for either class)","author":{"url":"https://github.com/dsyleixa","@type":"Person","name":"dsyleixa"},"datePublished":"2023-07-09T13:06:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/5/QtGameTutorial/issues/5"}