How to hide all the Items created in one particular loop in Qt?

Question

I have been using Qt Creator for almost a month now. I hope this is not a silly question because it bugged me for a long time.

I want to achieve:

• 1. create many different items(let's say 20 per sec) in QGraphicsScene.
• 2. use one single class for all these items
• 3. mark all these items, delete or hide them when a signal is triggered.

After trying a lot of methods, the best way I see is to use QGraphicsItemGroup. I tried to group all of them into a QGraphicsItemGroup. But after adding an item into a group, the item refuses to show on the scene any more, no matter what functions I use from library.

Is there something which I did wrongly in using the QGraphicsItemGroup? Or are there any other better apporaches?

Looking forward to anyone's help. Really appreciated.

Followed is a structure of my code:

// ......
QGraphicsItemGroup *myItemsGroup = new QGraphicsItemGroup
timer->start(100);
connect(timer,SIGNAL(timeout()),this,SLOT(draw_trail()));
// ......
void MyFunction::draw_trail()
{
    Trail_item *new_item = new Trail_item;
    scene->addItem(new_item);
    new_item->setX(COPX-7);    
    new_item->setY(COPY-7);
    new_item->setZValue(5);
    /* 
    then I started trying add to group
    //myItemsGroup->addToGroup(new_item)
    after adding this line, the item vanishes.
    */
}

(note: trail_item is a item class I created. Since it is a loop, I don't know how to change *new_item pointer name, so all items have the same name.)

Answer 1

Make sure that you have added the QGraphicsItemGroup in the scene, and that the QGraphicsItemGroup is visible.

You can add the QGraphicsItemGroup to the scene as any other QGraphicsItem, using the method QGraphicsScene::addItem(QGraphicsItem*)