1 files changed, 56 insertions, 0 deletions
diff --git a/examples/tools/offsetvector/randomlistmodel.cpp b/examples/tools/offsetvector/randomlistmodel.cpp
new file mode 100644
index 0000000..5c0953b
--- /dev/null
+++ b/examples/tools/offsetvector/randomlistmodel.cpp
@@ -0,0 +1,56 @@
+#include "randomlistmodel.h"
+
+static const int bufferSize(500);
+static const int lookAhead(100);
+static const int halfLookAhead(lookAhead/2);
+
+RandomListModel::RandomListModel(QObject *parent)
+: QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
+{
+}
+
+RandomListModel::~RandomListModel()
+{
+}
+
+int RandomListModel::rowCount(const QModelIndex &) const
+{
+    return m_count;
+}
+
+//! [0]
+QVariant RandomListModel::data(const QModelIndex &index, int role) const
+{
+    if (role != Qt::DisplayRole)
+        return QVariant();
+
+    int row = index.row();
+
+    if (row > m_rows.lastIndex()) {
+        if (row - m_rows.lastIndex() > lookAhead)
+            cacheRows(row-halfLookAhead, qMin(m_count, row+halfLookAhead));
+        else while (row > m_rows.lastIndex())
+            m_rows.append(fetchRow(m_rows.lastIndex()+1));
+    } else if (row < m_rows.firstIndex()) {
+        if (m_rows.firstIndex() - row > lookAhead)
+            cacheRows(qMax(0, row-halfLookAhead), row+halfLookAhead);
+        else while (row < m_rows.firstIndex())
+            m_rows.prepend(fetchRow(m_rows.firstIndex()-1));
+    }
+
+    return m_rows.at(row);
+}
+
+void RandomListModel::cacheRows(int from, int to) const
+{
+    for (int i = from; i <= to; ++i)
+        m_rows.insert(i, fetchRow(i));
+}
+//![0]
+
+//![1]
+QString RandomListModel::fetchRow(int position) const
+{
+    return QString::number(rand() % ++position);
+}
+//![1]