4. Replace QstandItemModel with QAbstractItemModel

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Replace QstandItemModel with QAbstractItemModel


  • Hi,

    I was wondering if someone can help me with a problem I'm having using QStandardItemModel and perhaps show me to migrate my code to QAbstractItemModel. I have a tree view which is being populated using QStandardItemModel . The problem is when I try to remove rows; a lot of them it takes a long time. An example is removing 40,000+ rows. This used to work fine with Qt versions < 5.11.2. But now I'm migrated to 5.12 and it is extremely slow. Suggestions from others is to use QAbstractItemModel and remove the rows using that model. Below is a sample program which works fine with earlier version of Qt ( < 5.11.2 ).

    Can someone show me how to map to QAbstractItemModel or make it work just as fast with QStandardItemModel using the current version of Qt? I did a lot of reading but still don't understand how to do it. I'm fairly new to Qt so I need detail help if possible. I just need to know how to add data to the model for QAbstractItemModel equivalent to QStandardItemModel::setItem and how to remove rows equivalent to QStandardItemModel::removeRows.

    Regards,
    Dan

    #include <QtWidgets>

    //QAbstractItemModel Class
    void executeTest()
    {
    int masterRowNumber = 0;
    const int numberOfRows = 50000;
    const int removeRows = 40000;
    const int numCol = 15;

    QTreeView tv;
QStandardItemModel myModel;
QElapsedTimer timer;
timer.start();

qDebug() << "creating first set of data";

//Now that we have our data lets put into the model
tv.setModel(&myModel);
tv.setUniformRowHeights(true);  //Speeds up scrolling
tv.setSortingEnabled(true);  //enable sorting

for (int row = 0; row < numberOfRows; row++)
{
    //Inserting data into the model
    for (int col = 0; col < numCol; col++)
        myModel.setItem(row, col, new QStandardItem(QString::number(row)));

    masterRowNumber++;
}

qDebug() << "After first Insert into model" << timer.elapsed();
qDebug() << "Now Deleting Data...";

//sort the data - in the treeView
tv.sortByColumn(2, Qt::AscendingOrder);  //this causes a long deley in delete

//Now that our model is populated and shown in the treeView - lets delete rows
// **** It takes forever to delete the first set of rows after the sort.  
//In 5.12 This is very SLOW!!! but fast in Qt < 5.11.2
tv.setSortingEnabled(false);
myModel.removeRows(0, removeRows, QModelIndex());  //remove 40000 rows
tv.setModel(&myModel);
tv.setSortingEnabled(true);
masterRowNumber -= removeRows;

qDebug() << "After first delete of rows now creating new set of data"  << timer.elapsed();

//now lets add more rows again
for (int row = 0; row < numberOfRows; row++)
{
    //Inserting data into the model
    for (int col = 0; col < numCol; col++)
       myModel.setItem(masterRowNumber, col, new QStandardItem(QString::number(row)));

    masterRowNumber++;
}

qDebug() << "After second insert into model"  << timer.elapsed();
qDebug() << "Now Deleting..";

//Again very slow!
tv.setSortingEnabled(false);
myModel.removeRows(0, removeRows, QModelIndex());  //remove 40000 rows
tv.setSortingEnabled(true);
masterRowNumber -= removeRows;

qDebug() << "After second delete"  << timer.elapsed();


qDebug() << "finished";

    }

    int main(int argc, char *argv[])
    {
    QApplication a(argc, argv);
    executeTest();

    return a.exec();

    }

    0 1 Reply

  • @leinad said in Replace QstandItemModel with QAbstractItemModel:

    Suggestions from others is to use QAbstractItemModel and remove the rows using that model.

    I doubt it's going to solve anything. smells like a view problem.

    What is the resize policy you set on the headers of the view?

    1

  • Is this what you mean?

    ui->topTreeView->setUniformRowHeights(true);

    0 1 Reply
  • Lifetime Qt Champion

    @leinad
    Hi
    I think more like something like
    treeWidget->header()->setStretchLastSection(true);
    or
    treeWidget->header()->setSectionResizeMode(QHeaderView::ResizeToContents);

    0 1 Reply

  • @mrjj said in Replace QstandItemModel with QAbstractItemModel:

    treeWidget->header()->setSectionResizeMode(QHeaderView::ResizeToContents);

    Both did not work. It can easily be tested in the sample code provided. The thing is remove rows worked perfectly fine and fast prior to 5.11.2. I don't see how setting the header will speed up removing rows from the model. I'm guessing I really need to subclass using QAbstractItemModel. Any help in doing that would be great.

    0
  • Lifetime Qt Champion

    @mrjj It's due a change in QStandardItemModel - see https://bugreports.qt.io/browse/QTBUG-78324 but I've no idea how to fix it without reverting the change. Therefore going to a custom model is (sadly) currently the way to go.

    2

  • This is why I respectfully request how to do this. I'm trying using the following example: https://doc.qt.io/qt-5/qtwidgets-itemviews-simpletreemodel-example.html but running into issues.

    0
  • Lifetime Qt Champion

    Your example above uses a QTreeView but the data model looks like a table - so what do you need?

    0

  • I need it work with a treeview. You can see that "tv" is initialized as a treeview. Basically the code above using treeview and abstract model. After that I can figure how to replace my larger base code with this simple example. That is all I need.

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  • Lifetime Qt Champion

    @leinad said in Replace QstandItemModel with QAbstractItemModel:

    You can see that "tv" is initialized as a treeview

    It does not matter what view you are using but what model you really use - your example code clearly shows us a table structure, not a tree structure - therefore my question...

    0

  • Its a table but I treat it like a tree which just a bunch of columns and rows like a spreadsheet. There is nothing fancy like children, grandchildren, etc.

    0
  • Lifetime Qt Champion

    So you don't need to implement a tree model and can use QAbstractTableModel as base instead which is much easier.

    0

  • Well, all my code is already around a treeview so I would prefer to stay that course. I would have to change the GUI plus the code which seems much more invasive. This is not a small project.

    0

  • I'm sorry, I misread what you are saying. I can look at using a QAbstractTableModel. Do you think the performance will be a good as it was before all of this?

    0

  • I have this code fragment which I'm having issues. I'm using QAbstractTableModel as suggested.

    topTreeViewModel = new TopTreeViewModel();

    void TopTreeViewModel::insertRowsIntoModel(int rowNumber, QList<QList<QStandardItem *>> QStandardItemList, TopTreeViewModel *model, QModelIndex parent)
    {
    beginInsertRows(QModelIndex(), rowNumber, rowNumber + QStandardItemList[0].size() - 1); //QModelIndex, rowNumber, numberOfRows
    model->insertRows(rowNumber, QStandardItemList[0].size(), parent);
    for(int rows = 0; rows < QStandardItemList.size(); rows++)
    {

        for(int col = 0; col < QStandardItemList[rows].size(); col++)
    {
        QModelIndex index = model->index(rowNumber + rows, col, parent);
        model->setData(index, QStandardItemList[rows][col]->text(), Qt::DisplayRole);
    }
}
endInsertRows();
emit(dataChanged(parent, parent));

    }

    I call it by using the following in another mainWindow:

    metaDataModel->insertRowsIntoModel(rowNumber, QStandardItemList, metaDataModel, parent);
    rowNumber += QStandardItemList.size();

    I get an exception in beginInsertRows(); If I comment it out the data is correct but not displayed in the treeView.

    The header is declared as follows (there are other methods but this is the one causing issues. Any help?
    #ifndef TOPTREEVIEWMODEL_H
    #define TOPTREEVIEWMODEL_H

    #include <QObject>
#include <QAbstractTableModel>
#include <QStandardItem>
#include <QDebug>

    class TopTreeViewModel : public QAbstractTableModel
    {
    Q_OBJECT

    public:
    TopTreeViewModel(QObject *parent=0);
    ~TopTreeViewModel();

    public:

    void insertRowsIntoModel(int rowNumber, QList<QList<QStandardItem *>> QStandardItemList, TopTreeViewModel *model, QModelIndex parent);

    };

    #endif // TOPTREEVIEWMODEL_H

    0 1 Reply

  • @leinad
    I haven't attempted to follow all your code, but:

    beginInsertRows(QModelIndex(), rowNumber, rowNumber + QStandardItemList[0].size() - 1); //QModelIndex, rowNumber, numberOfRows
model->insertRows(rowNumber, QStandardItemList[0].size(), parent);
for(int rows = 0; rows < QStandardItemList.size(); rows++)

    This does not look right, does it? For the "I get an exception in beginInsertRows();", I think you mean in the arguments to calling that function. There must be something fundamentally wrong in counting the required rows via QStandardItemList[0].size() but indexing/looping via rows < QStandardItemList.size(). The first has [0], the second does not. I would guess the latter is correct, and QStandardItemList[0].size() is to do with column count? Or maybe I'm going mad....

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