From https://doc.qt.io/qt-5/model-view-programming.html

Using Models and Views

The following sections explain how to use the model/view pattern in Qt. Each section includes an example and is followed by a section showing how to create new components.

Two models included in Qt

Two of the standard models provided by Qt are QStandardItemModel and QFileSystemModel.

• QStandardItemModel is a multi-purpose model that can be used to represent various different data structures needed by list, table, and tree views. This model also holds the items of data.
• QFileSystemModel is a model that maintains information about the contents of a directory. As a result, it does not hold any items of data itself, but simply represents files and directories on the local filing system.

Using views with an existing model

The QListView and QTreeView classes are the most suitable views to use with QFileSystemModel.

The example presented below displays the contents of a directory in a tree view next to the same information in a list view. The views share the user's selection so that the selected items are highlighted in both views.

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We set up a QFileSystemModel so that it is ready for use, and create some views to display the contents of a directory. This shows the simplest way to use a model. The construction and use of the model is performed from within a single main() function:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QSplitter *splitter = new QSplitter;

    QFileSystemModel *model = new QFileSystemModel;
    model->setRootPath(QDir::currentPath());

    QTreeView *tree = new QTreeView(splitter);
    tree->setModel(model);
    tree->setRootIndex(model->index(QDir::currentPath()));

    QListView *list = new QListView(splitter);
    list->setModel(model);
    list->setRootIndex(model->index(QDir::currentPath()));

    splitter->setWindowTitle("Two views onto the same file system model");
    splitter->show();
    return app.exec();
}

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• The model is set up to use data from a certain file system. The call to setRootPath() tells the model which drive on the file system to expose to the views.
• We create two views so that we can examine the items held in the model in two different ways:
• The views are constructed in the same way as other widgets. Setting up a view to display the items in the model is simply a matter of calling its setModel() function with the directory model as the argument. We filter the data supplied by the model by calling the setRootIndex() function on each view, passing a suitable model index from the file system model for the current directory.
• The index() function used in this case is unique to QFileSystemModel; we supply it with a directory and it returns a model index. Model indexes are discussed in Model Classes.
• In the above example, we neglected to mention how to handle selections of items. This subject is covered in more detail in the section about Handling Selections in Item Views.

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