QTreeView doesn’t display anything from custom model
Hello!
I have a custom model which is descendant of QAbstractItemModel and I have a custom tree view which is descendant of QTreeView(it implements several events and doesn’t violate any logic). At the start I have no elements in the model but the root element. Interactively I’m adding new elements to the model and they are added to the model correctly.
The problem is that I have only a blank rectangle in place of my tree. Any my rows manipulation does nothing and I don’t understand what the trouble is. I’m using beginInsertRows\endInsertRows pairs and it doesn’t help.
Can anybody explain why such a thing can be?
9 replies
Last time I had this, i forgot to respect the role parameter in the models data method. I just returned the data to display as a QString in a variant independent from the role parameter.
But actually one of the roles was the size of the field to show the string in the QItemList. Maybe the problem is similiar….
But without a small code example …..
Maybe there are problems with linking parent and children?
No, link works as it should.
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- return 0;
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- return static_cast<int>(pItem->ChildCount());
- }
- int Role) const
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- return pItem->Data(Role);
- }
- {
- TRACE_LOG("Start routine");
- if (!Index.isValid())
- return 0;
- }
- int Column,
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- return RootElement();
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- AccountItem::ChildType Child = pItem->Child(static_cast<size_t>(Row));
- if(Child != c_InvalidChild)
- return createIndex(Row, Column, static_cast<void*>(Child));
- }
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- AccountItem* pParent = pItem->Parent();
- //It is a one of the children...
- if(pParent != nullptr)
- return createIndex(pParent->Position(), 0, static_cast<void*>(pParent));
- //... or it is the root element.
- else
- }
- int Role /*= Qt::EditRole*/)
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- return false;
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- pItem->SetData(Role, Value);
- return true;
- }
- bool AccountModel::insertRows(int Row,
- int Count,
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- return false;
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- if(pItem->ChildCount() < static_cast<size_t>(Row) || Row < 0)
- return false;
- beginInsertRows(Index, Row, Row + Count - 1);
- for(int i = Row; i < Row + Count; ++i)
- {
- AccountItem* pNewItem = new AccountItem(nullptr);
- if(!pItem->InsertChild(pNewItem, static_cast<size_t>(i)))
- {
- WARN_LOG("Unable to insert child");
- delete pNewItem;
- return false;
- }
- }
- endInsertRows();
- return true;
- }
- {
- TRACE_LOG("Start routine");
- if(!Index.isValid())
- return false;
- AccountItem* pItem = static_cast<AccountItem*>(Index.internalPointer());
- Q_ASSERT(pItem != nullptr);
- return pItem->ChildCount();
- }
I have another question related to the topic.
When I create model with the only one element(actually the top root element) QTreeView doesn’t show anything. It waits until the root gets at least one child and then start to draw my tree. And when it draws the tree it uses only the top root index and displays only one element. But I have two elements! It seems weird to me. Why QTreeView doesn’t show element if it is the only one element and it was selected as the tree root? And why it shows only one element after I add child to the top root and use Model Index of the top root instead of the child index when retrieve its data?
Last time I had this, i forgot to respect the role parameter in the models data method. I just returned the data to display as a QString in a variant independent from the role parameter.
Thank you!
For those who experiance this problem, I’ll describe my own case (maybe a common one). I had this simple data():
- switch (role) {
- return "o_O";
- default:
- return false;
- }
and my tree view looked empty.
After reading this thread, I added debug output to this method and understood that the first and the only role that was asked to my model was role=13 (Qt::SizeHintRole). As soon as I returned false, the tree decided not to ask any more data for any cell.
So, this version of data() worked better:
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