Fetch More Example

FileListModel Class Implementation

We start by checking out the setDirPath().

 void FileListModel::setDirPath(const QString &path)
 {
     QDir dir(path);

     fileList = dir.entryList();
     fileCount = 0;
     reset();
 }

We use a QDir to get the contents of the directory. We need to inform QAbstractItemModel that we want to remove all items - if any - from the model.

 bool FileListModel::canFetchMore(const QModelIndex & /* index */) const
 {
     if (fileCount < fileList.size())
         return true;
     else
         return false;
 }

The canFetchMore() function is called by the view when it needs more items. We return true if there still are entries that we have not added to the model; otherwise, we return false.

And now, the fetchMore() function itself:

 void FileListModel::fetchMore(const QModelIndex & /* index */)
 {
     int remainder = fileList.size() - fileCount;
     int itemsToFetch = qMin(100, remainder);

     beginInsertRows(QModelIndex(), fileCount, fileCount+itemsToFetch);

     fileCount += itemsToFetch;

     endInsertRows();

     emit numberPopulated(itemsToFetch);
 }

We first calculate the number of items to fetch. beginInsertRows() and endInsertRows() are mandatory for QAbstractItemModel to keep up with the row insertions. Finally, we emit numberPopulated(), which is picked up by Window.

To complete the tour, we also look at rowCount() and data().

 int FileListModel::rowCount(const QModelIndex & /* parent */) const
 {
     return fileCount;
 }

 QVariant FileListModel::data(const QModelIndex &index, int role) const
 {
     if (!index.isValid())
         return QVariant();

     if (index.row() >= fileList.size() || index.row() < 0)
         return QVariant();

     if (role == Qt::DisplayRole)
         return fileList.at(index.row());
     else if (role == Qt::BackgroundRole) {
         int batch = (index.row() / 100) % 2;
         if (batch == 0)
             return qApp->palette().base();
         else
             return qApp->palette().alternateBase();
     }
     return QVariant();
 }

Notice that the row count is only the items we have added so far, i.e., not the number of entries in the directory.

In data(), we return the appropriate entry from the fileList. We also separate the batches with a different background color.