Presetting a combobox to one of its tree view popup entry

Bert59 · 2 Apr 2021, 00:43

Hi,
I have a combobox with a popup treeview as shown below.

I would like to set the combobox current item programmaticaly to one of the child items.

How can I achieve that ?

Bert59 · 27 Oct 2022, 15:31

Finally I found a way to make it work.
First I have created a subclass for QCombobox called TreeBox.

TreeBox::TreeBox(QWidget *parent) : QComboBox(parent)
{
    m_tree = new QTreeView;
    this->setView(m_tree);

    m_tree->setHeaderHidden(true);
    m_tree->viewport()->installEventFilter(this);
}

Then in the class which is using the TreeBox I have declared a private property to keep track of the items added to the list view.

QVector<QStandardItem*> m_itemList;
QStandardItemModel m_modelForTree;

In the ui I have added a ComboBox and promoted it to TreeBox.
Then I populate the tree model as follows and set the model to the ComboBox.

QStandardItem *root = m_modelForTree.invisibleRootItem();
    QStandardItem *item;
    for (int i=0; i<10; i++){
        item = new QStandardItem(QString("item %0").arg(i));
        m_itemList.append(item);
        root->appendRow(item);
        for(int j=0; j<5; j++){
            item->setChild(j, 0, new QStandardItem(QString("item %0%1").arg(i).arg(j)));
        }
    }

    ui->comboBox->setModel(&m_modelForTree);

As an example I choose "item 43" to be set at the startup of this test program.

QString text = "item 43";

Then I loop through the QStandardListItems in m_itemList to find the QModelIndex of the item I want to preset.

bool textFound=false;
    QModelIndex modelIndex;
    for (int i=0; i<m_itemList.count(); i++){
        for (int j=0; j<m_itemList[i]->rowCount(); j++){
            modelIndex = m_modelForTree.indexFromItem(m_itemList[i]->child(j));
            if (modelIndex.data(Qt::DisplayRole).toString()==text){
                textFound = true;
                break;
            }
        }
        if (textFound)
            break;
    }

Now I can set the item as follows

ui->comboBox->setRootModelIndex(modelIndex.parent());
ui->comboBox->setCurrentIndex(modelIndex.row());

Unfortunately this restricts also the items displayed in the popup of the combobox to those of the current parent item.

To avoid this behavior I have to reset to the first QStandardItem in the list

    modelIndex = m_modelForTree.indexFromItem(m_itemList[0]);
    ui->comboBox->setRootModelIndex(modelIndex.parent());

Now I get the behaviour I was looking for

Maybe there are simpler ways to do it and I would be glad if someone could come up with one.
But for the time being I just wanted to share this solution.

Pl45m4 · B Bert59 1 Apr 2021, 19:56

@Bert59

Check what index they have and then just setCurrentIndex(idx).

Bert59 · 2 Apr 2021, 07:29

But how do I get the index of an item? If I just now the name, for example "item 24", how can I get the index for it?

JonB · 4 Feb 2021, 07:34

@Bert59
You must search the tree view items for the one matching item 24. You could try QComboBox::findText() to do that, I don't know if it works for you but worth a try.

If you say all you want to do is set the current item, have you tried simply yourComboBox->setCurrentText("item 24")? I don't know whether that will work with a tree view, and selecting a sub-item, but again worth a try?

Bert59 · 2 Apr 2021, 07:46

Thank you for the feedback.
Unfortunately both methods only work for the root items (item 2 for example) but not for the child items like "item 24".

JonB · 4 Feb 2021, 07:49

@Bert59
Yes I did wonder if that might be the case.

That only means you cannot use the two quick ...text() methods. Revert to what I said first (which is what ...text() methods would have to do internally anyway): search the tree view/model for the item you want. I assume you have tested that setCurrentIndex(7) does indeed select item 24 correctly, so you know all you have to do is correctly find that item 24 is at item #7 and it will then select correctly? (If it does not do that, and actually selects item 7 which is presumably scrolled down at the bottom, then you have a problem....)

Bert59 · 2 Apr 2021, 08:05

setCurrentIndex(7) selects in fact "item 7".

I think I should use ui->comboBox->view()->setCurrentIndex(index);

But in this method index is a QModelIndex and so far I couldn't find a way to get the QModelIndex from the items name.

JonB · 4 Feb 2021, 08:05

@Bert59 said in Presetting a combobox to one of its tree view popup entry:

setCurrentIndex(7) selects in fact "item 7".

Then you should stop and realise this is telling you your whole idea is flawed/does not work.

A QComboBox works from a single, integer index, not a QModelIndex. Your finding shows that no value for QComboBox::setCurrentIndex() is going to select a non-top-level item/node such as item 24. Rather, it only works on the top-level items, and that's all it will allow you to select/return as selected. Even if you find item 24's QModelIndex in the model, how will that help you select/return it in a combo box?

QCombBox only works for a "flat" list of items. Not some tree view hierarchy. Where did you get the idea from that you could make it work with a tree view? Have you found any code example anywhere which says that can be done?

Bert59 · 27 Oct 2022, 15:31