添加到模型时 Qt QTreeView 不更新

Question

The source code relating to this question is available on my public Git repository on BitBucket .

I'm trying to dynamically add some items to a QTreeView model using the following code in mainwindow.cpp :

if(dlg->exec() == QDialog::Accepted) {
    QList<QVariant> qList;
    qList << item.name << "1111 0000" << "0x00";
    HidDescriptorTreeItem *item1 = new HidDescriptorTreeItem(qList, hidDescriptorTreeModel->root());
    hidDescriptorTreeModel->root()->appendChild(item1);
}

This works when run from within my MainWindow constructor, just after ui->setupUi(this) , but I need this to run from within an event filter, but the same code doesn't get the QTreeView updating. When I set a breakpoint at mainwindow.cpp:70 and step through the next few lines, I can see the data is being added to the Model, but I need the QTreeView to refresh.

I understand this is done by emitting dataChanged() , but not really sure how to do this. The signal signature for the dataChanged signal looks as follows:

void dataChanged(const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles = QVector<int>());

so I need to come up with topLeft and bottomRight QModelIndex instances. How do I build/obtain these from item1 in the above snippet?

Also, where does beginInsertRows() and endInsertRows() come into view with this, should I be calling these functions?

Answer 1

From QAbstractItemModel documentation:

void QAbstractItemModel::beginInsertRows ( const QModelIndex & parent, int first, int last ) [protected]
Begins a row insertion operation.
When reimplementing insertRows() in a subclass, you must call this function before inserting data into the model's underlying data store.
The parent index corresponds to the parent into which the new rows are inserted; first and last are the row numbers that the new rows will have after they have been inserted.

The other protected functions say similar things.

And insertRows() says:

If you implement your own model, you can reimplement this function if you want to support insertions. Alternatively, you can provide your own API for altering the data. In either case , you will need to call beginInsertRows() and endInsertRows() to notify other components that the model has changed.

Take a look to QAbstractItemModel protected functions and signals

Views connect to those signals to know when model data changes and rearrange data inside. The functions emit the signals internally to make it easy for you to warn the view when it has happenned. But signals can only be emitted by abstract class.

Components connected to this signal use it to adapt to changes in the model's dimensions. It can only be emitted by the QAbstractItemModel implementation, and cannot be explicitly emitted in subclass code.

So you will have to stick to the methods.

Edit in answer to your comment:

Indeed, Items should have a reference to model and tell it about changes, check theses lines from QStandardItem:

void QStandardItem::emitDataChanged()

void QStandardItem::removeRows(int row, int count)

( Note, how, in second, it calls model's rowsAboutToBeRemoved() and rowsRemoved() )

Maybe you should try to use QStandardItem and QStandardItemModel . Either direct or subclassing. It will hide a lot of ugly stuff.

Answer 2

There's also a less proper but much easier way to achieve this - emit layoutChanged() instead of dataChanged() . More info - https://stackoverflow.com/a/41536459/635693