How to build a Qt tree widget step by step, when the user clicks on the branches?

Question

I built a large tree whose branches are loaded from disk, an operation that takes 5 minutes to complete. To speed it up, I want to only load the sub-trees the user selects from the GUI.

This is the current code, that loads everything all at once:

int MyWidget::AddSubtree(QTreeWidgetItem *_projectItem,
                         const QString &_filePath)
{
    const QString currentPrj = _projectItem->text(0);
    QDir* rootDir = new QDir(_filePath);
    QFileInfoList filesList = rootDir->entryInfoList();

    filesList = rootDir->entryInfoList();

    foreach(QFileInfo fileInfo, filesList)
    {
        if(fileInfo.isDir())
        {
            const QString job = fileInfo.fileName();

            QTreeWidgetItem* jobItem = new QTreeWidgetItem();
            jobItem->setText(0, job);

            //+P Performance critical! Do it on demand
            AddSubSubtree(jobItem, fileInfo.filePath());

            _projectItem->addChild(jobItem);
        }
    }

    return 0;
}


int MyWidget::AddSubSubtree(QTreeWidgetItem *_jobItem,
                            const QString &_filePath)
{
    const QString currentJob = _jobItem->text(0);
    QDir* rootDir = new QDir(_filePath);
    rootDir->cd("subDir");

    // Retrieve the runs

    filesList = rootDir->entryInfoList();

    foreach(QFileInfo fileInfo, filesList)
    {
        if(fileInfo.isDir())
        {
            const QString run = fileInfo.fileName();

            QTreeWidgetItem* runItem = new QTreeWidgetItem();
            runItem->setText(0, run);

            _jobItem->addChild(runItem);
        }
    }

    return 0;
}

What I would like to do is to remove the performance critical line (below //+P), and call AddSubSubtree() on a single sub-sub-tree just when the user clicks on the corresponding parent branch.

How can I detect a specific parent branch has been clicked?

I know I need something like this in AddSubtree:

connect(jobItem, SIGNAL(triggered()), this, SLOT(AddSubSubtree()));

but I cannot make it work.
Am I lost in the details, or am I on a completely wrong path?

If performance is important, your approach will not be fast enough by definition. You need to implement your tree view differently and Qt provides such framework. It called "Model/View architecture". You can refer this tutorial for details: http://qt-project.org/doc/qt-4.8/modelview.html — vahancho, Sep 26 '13 at 11:03

score 2 · Answer 1 · answered Sep 26 '13 at 11:03

I think you may be looking for the signal itemClicked(QTreeWidgetItem * item, int column) from QTreeWidget. I'd try something like:

connect(yourTree, SIGNAL(itemClicked()), yourTree, SLOT(AddSubTree()));

You'd have to subclass TreeWidget and make AddSubTree(QTreeWidgetItem* item, int column) a slot of that subclass. Then in AddSubTree, check the column number is right and if so add the appropriate sub-tree to the argument item.

score 1 · Answer 2 · answered Sep 26 '13 at 11:06

1

you might wish to port to a QAbstractItemModel and a QTreeView

where you implement the QAbstractItemModel to return the data and use canFetchMore(QModelIndex&) and fetchMore to do the actual fetching

answered Sep 26 '13 at 11:06

ratchet freak

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How to build a Qt tree widget step by step, when the user clicks on the branches?

2 Answers2