how to delete single item from QAbstractTableModel?

johnby

I am trying to remove a single row and have overridden removeRow() in MyModel.

class MyModel : public QAbstractTableModel
{
    QList<MyObject> objects;

    public:
        // ...
    
        bool removeRow(int row, const QModelIndex &parent = QModelIndex());
};

The QAbstractItemModel::removeRow(...) docs say this.

This is a convenience function that calls removeRows().

And so in removeRow() I have the following, but I'm not sure how this should work. Do I have to call removeRows()?

bool MyModel::removeRow(int row, const QModelIndex &parent)
{
    beginRemoveRows(parent, first, row); ????

    objects.removeAt(row);

    endRemoveRows();

    return true;
}

nagesh

In beginRemoveRows function second and third argument should be same, as it's deleting single row.

beginRemoveRows(parent, row, row);

Application should call removeRow function whenever the particular row to be deleted.
Refer addressbook program provided in the Qt Examples

jeremy_k

Override QAbstractItemModel::removeRows rather than QAbstractItemModel::removeRow.
The function signatures are:

virtual bool removeRows(int row, int count, const QModelIndex &parent);
inline bool removeRow(int row, const QModelIndex &parent);

Note that removeRows is virtual, but removeRow is inline.

JonB

@jeremy_k
I guess that is the case so that you are free to write your own removeRows() to remove multiple rows in a more efficient fashion than calling removeRow() multiple times, if that suits your impementation?

jeremy_k

I would phrase it must rather than are free to if either removeRow or removeRows are used via a QAbstractItemModel pointer.

Otherwise:

inline bool QAbstractItemModel::removeRow(int arow, const QModelIndex &aparent)
{ return removeRows(arow, 1, aparent); }

Which leads to:

bool QAbstractItemModel::removeRows(int, int, const QModelIndex &)
{
    return false;
}

JonB

@jeremy_k
Yes indeed! I didn't look, I had assumed removeRows() called removeRow() repeatedly, when in fact it is removeRow() which calls removeRows() once!

johnby

I noticed you guys didn't write

beginRemoveRows(...);
// ...
endRemoveRows();

Are these not necessary within the removeRow(s) calls?

jeremy_k

@johnby said in how to delete single item from QAbstractTableModel?:

I noticed you guys didn't write
beginRemoveRows(...);
// ...
endRemoveRows();
Are these not necessary within the removeRow(s) calls?

They are necessary, and they should be used in the implementation of removeRows().