diff --git a/src/xlsx/xlsxcontenttypes.cpp b/src/xlsx/xlsxcontenttypes.cpp
index 08c43e0..2288dea 100755
--- a/src/xlsx/xlsxcontenttypes.cpp
+++ b/src/xlsx/xlsxcontenttypes.cpp
@@ -111,7 +111,7 @@ void ContentTypes::addVbaProject()
     addOverride(QStringLiteral("bin"), QStringLiteral("application/vnd.ms-office.vbaProject"));
 }
 
-void ContentTypes::saveToXmlFile(QIODevice *device)
+void ContentTypes::saveToXmlFile(QIODevice *device) const
 {
     QXmlStreamWriter writer(device);
 
diff --git a/src/xlsx/xlsxcontenttypes_p.h b/src/xlsx/xlsxcontenttypes_p.h
index 512a592..2cca45d 100755
--- a/src/xlsx/xlsxcontenttypes_p.h
+++ b/src/xlsx/xlsxcontenttypes_p.h
@@ -65,7 +65,7 @@ public:
     void addCalcChain();
     void addVbaProject();
 
-    void saveToXmlFile(QIODevice *device);
+    void saveToXmlFile(QIODevice *device) const;
 
 private:
     QMap<QString, QString> m_defaults;
diff --git a/src/xlsx/xlsxdocpropsapp.cpp b/src/xlsx/xlsxdocpropsapp.cpp
index 9fcd809..36c9ed5 100755
--- a/src/xlsx/xlsxdocpropsapp.cpp
+++ b/src/xlsx/xlsxdocpropsapp.cpp
@@ -79,7 +79,7 @@ QStringList DocPropsApp::propertyNames() const
     return m_properties.keys();
 }
 
-void DocPropsApp::saveToXmlFile(QIODevice *device)
+void DocPropsApp::saveToXmlFile(QIODevice *device) const
 {
     QXmlStreamWriter writer(device);
     QString vt = QStringLiteral("http://schemas.openxmlformats.org/officeDocument/2006/docPropsVTypes");
@@ -130,7 +130,7 @@ void DocPropsApp::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-QByteArray DocPropsApp::saveToXmlData()
+QByteArray DocPropsApp::saveToXmlData() const
 {
     QByteArray data;
     QBuffer buffer(&data);
diff --git a/src/xlsx/xlsxdocpropsapp_p.h b/src/xlsx/xlsxdocpropsapp_p.h
index a2c04f3..2324c9a 100755
--- a/src/xlsx/xlsxdocpropsapp_p.h
+++ b/src/xlsx/xlsxdocpropsapp_p.h
@@ -58,8 +58,8 @@ public:
     QString property(const QString &name) const;
     QStringList propertyNames() const;
 
-    QByteArray saveToXmlData();
-    void saveToXmlFile(QIODevice *device);
+    QByteArray saveToXmlData() const;
+    void saveToXmlFile(QIODevice *device) const;
     static DocPropsApp loadFromXmlFile(QIODevice *device);
     static DocPropsApp loadFromXmlData(const QByteArray &data);
 
diff --git a/src/xlsx/xlsxdocpropscore.cpp b/src/xlsx/xlsxdocpropscore.cpp
index b3b6b7f..2bde22f 100644
--- a/src/xlsx/xlsxdocpropscore.cpp
+++ b/src/xlsx/xlsxdocpropscore.cpp
@@ -72,7 +72,7 @@ QStringList DocPropsCore::propertyNames() const
     return m_properties.keys();
 }
 
-void DocPropsCore::saveToXmlFile(QIODevice *device)
+void DocPropsCore::saveToXmlFile(QIODevice *device) const
 {
     QXmlStreamWriter writer(device);
     const QString cp = QStringLiteral("http://schemas.openxmlformats.org/package/2006/metadata/core-properties");
@@ -124,7 +124,7 @@ void DocPropsCore::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-QByteArray DocPropsCore::saveToXmlData()
+QByteArray DocPropsCore::saveToXmlData() const
 {
     QByteArray data;
     QBuffer buffer(&data);
diff --git a/src/xlsx/xlsxdocpropscore_p.h b/src/xlsx/xlsxdocpropscore_p.h
index 0ac5b4f..6a8e717 100644
--- a/src/xlsx/xlsxdocpropscore_p.h
+++ b/src/xlsx/xlsxdocpropscore_p.h
@@ -53,8 +53,8 @@ public:
     QString property(const QString &name) const;
     QStringList propertyNames() const;
         
-    void saveToXmlFile(QIODevice *device);
-    QByteArray saveToXmlData();
+    void saveToXmlFile(QIODevice *device) const;
+    QByteArray saveToXmlData() const;
     static DocPropsCore loadFromXmlFile(QIODevice *device);
     static DocPropsCore loadFromXmlData(const QByteArray &data);
 
diff --git a/src/xlsx/xlsxdrawing.cpp b/src/xlsx/xlsxdrawing.cpp
index 46f82a4..c8bbd6d 100644
--- a/src/xlsx/xlsxdrawing.cpp
+++ b/src/xlsx/xlsxdrawing.cpp
@@ -36,7 +36,7 @@ Drawing::Drawing()
     orientation = 0;
 }
 
-void Drawing::saveToXmlFile(QIODevice *device)
+void Drawing::saveToXmlFile(QIODevice *device) const
 {
     QXmlStreamWriter writer(device);
 
@@ -60,7 +60,7 @@ void Drawing::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-void Drawing::writeTwoCellAnchor(QXmlStreamWriter &writer, int index, XlsxDrawingDimensionData *data)
+void Drawing::writeTwoCellAnchor(QXmlStreamWriter &writer, int index, XlsxDrawingDimensionData *data) const
 {
     writer.writeStartElement(QStringLiteral("xdr:twoCellAnchor"));
     if (data->drawing_type == 2)
@@ -96,7 +96,7 @@ void Drawing::writeTwoCellAnchor(QXmlStreamWriter &writer, int index, XlsxDrawin
     writer.writeEndElement(); //xdr:twoCellAnchor
 }
 
-void Drawing::writeAbsoluteAnchor(QXmlStreamWriter &writer, int index)
+void Drawing::writeAbsoluteAnchor(QXmlStreamWriter &writer, int index) const
 {
     writer.writeStartElement(QStringLiteral("xdr:absoluteAnchor"));
     if (orientation == 0) {
@@ -113,21 +113,21 @@ void Drawing::writeAbsoluteAnchor(QXmlStreamWriter &writer, int index)
     writer.writeEndElement(); //xdr:absoluteAnchor
 }
 
-void Drawing::writePos(QXmlStreamWriter &writer, int x, int y)
+void Drawing::writePos(QXmlStreamWriter &writer, int x, int y) const
 {
     writer.writeEmptyElement(QStringLiteral("xdr:pos"));
     writer.writeAttribute(QStringLiteral("x"), QString::number(x));
     writer.writeAttribute(QStringLiteral("y"), QString::number(y));
 }
 
-void Drawing::writeExt(QXmlStreamWriter &writer, int cx, int cy)
+void Drawing::writeExt(QXmlStreamWriter &writer, int cx, int cy) const
 {
     writer.writeStartElement(QStringLiteral("xdr:ext"));
     writer.writeAttribute(QStringLiteral("cx"), QString::number(cx));
     writer.writeAttribute(QStringLiteral("cy"), QString::number(cy));
 }
 
-void Drawing::writeGraphicFrame(QXmlStreamWriter &writer, int index, const QString &name)
+void Drawing::writeGraphicFrame(QXmlStreamWriter &writer, int index, const QString &name) const
 {
     writer.writeStartElement(QStringLiteral("xdr:graphicFrame"));
     writer.writeAttribute(QStringLiteral("macro"), QString());
@@ -149,7 +149,7 @@ void Drawing::writeGraphicFrame(QXmlStreamWriter &writer, int index, const QStri
     writer.writeEndElement(); //xdr:graphicFrame
 }
 
-void Drawing::writePicture(QXmlStreamWriter &writer, int index, double col_abs, double row_abs, int width, int height, const QString &description)
+void Drawing::writePicture(QXmlStreamWriter &writer, int index, double col_abs, double row_abs, int width, int height, const QString &description) const
 {
     writer.writeStartElement(QStringLiteral("xdr:pic"));
 
diff --git a/src/xlsx/xlsxdrawing_p.h b/src/xlsx/xlsxdrawing_p.h
index 6733c08..a4a0f08 100644
--- a/src/xlsx/xlsxdrawing_p.h
+++ b/src/xlsx/xlsxdrawing_p.h
@@ -68,19 +68,19 @@ class Drawing
 {
 public:
     Drawing();
-    void saveToXmlFile(QIODevice *device);
+    void saveToXmlFile(QIODevice *device) const;
 
     bool embedded;
     int orientation;
     QList <XlsxDrawingDimensionData *> dimensionList;
 
 private:
-    void writeTwoCellAnchor(QXmlStreamWriter &writer, int index, XlsxDrawingDimensionData *data);
-    void writeAbsoluteAnchor(QXmlStreamWriter &writer, int index);
-    void writePos(QXmlStreamWriter &writer, int x, int y);
-    void writeExt(QXmlStreamWriter &writer, int cx, int cy);
-    void writeGraphicFrame(QXmlStreamWriter &writer, int index, const QString &name=QString());
-    void writePicture(QXmlStreamWriter &writer, int index, double col_abs, double row_abs, int width, int height, const QString &description);
+    void writeTwoCellAnchor(QXmlStreamWriter &writer, int index, XlsxDrawingDimensionData *data) const;
+    void writeAbsoluteAnchor(QXmlStreamWriter &writer, int index) const;
+    void writePos(QXmlStreamWriter &writer, int x, int y) const;
+    void writeExt(QXmlStreamWriter &writer, int cx, int cy) const;
+    void writeGraphicFrame(QXmlStreamWriter &writer, int index, const QString &name=QString()) const;
+    void writePicture(QXmlStreamWriter &writer, int index, double col_abs, double row_abs, int width, int height, const QString &description) const;
 };
 
 } // namespace QXlsx
diff --git a/src/xlsx/xlsxrelationships.cpp b/src/xlsx/xlsxrelationships.cpp
index 55cb99a..2616182 100755
--- a/src/xlsx/xlsxrelationships.cpp
+++ b/src/xlsx/xlsxrelationships.cpp
@@ -100,7 +100,7 @@ void Relationships::addRelationship(const QString &type, const QString &target,
     m_relationships.append(relation);
 }
 
-void Relationships::saveToXmlFile(QIODevice *device)
+void Relationships::saveToXmlFile(QIODevice *device) const
 {
     QXmlStreamWriter writer(device);
 
@@ -120,7 +120,7 @@ void Relationships::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-QByteArray Relationships::saveToXmlData()
+QByteArray Relationships::saveToXmlData() const
 {
     QByteArray data;
     QBuffer buffer(&data);
diff --git a/src/xlsx/xlsxrelationships_p.h b/src/xlsx/xlsxrelationships_p.h
index 3ed8be4..c1afee5 100755
--- a/src/xlsx/xlsxrelationships_p.h
+++ b/src/xlsx/xlsxrelationships_p.h
@@ -66,8 +66,8 @@ public:
     void addMsPackageRelationship(const QString &relativeType, const QString &target);
     void addWorksheetRelationship(const QString &relativeType, const QString &target, const QString &targetMode=QString());
 
-    void saveToXmlFile(QIODevice *device);
-    QByteArray saveToXmlData();
+    void saveToXmlFile(QIODevice *device) const;
+    QByteArray saveToXmlData() const;
     bool loadFromXmlFile(QIODevice *device);
     bool loadFromXmlData(const QByteArray &data);
     XlsxRelationship getRelationshipById(const QString &id) const;
diff --git a/src/xlsx/xlsxtheme.cpp b/src/xlsx/xlsxtheme.cpp
index 2029771..ee9a832 100755
--- a/src/xlsx/xlsxtheme.cpp
+++ b/src/xlsx/xlsxtheme.cpp
@@ -205,7 +205,7 @@ Theme::Theme()
 {
 }
 
-void Theme::saveToXmlFile(QIODevice *device)
+void Theme::saveToXmlFile(QIODevice *device) const
 {
     if (xmlData.isEmpty())
         device->write(defaultXmlData);
diff --git a/src/xlsx/xlsxtheme_p.h b/src/xlsx/xlsxtheme_p.h
index f67a4da..312c78e 100755
--- a/src/xlsx/xlsxtheme_p.h
+++ b/src/xlsx/xlsxtheme_p.h
@@ -46,7 +46,7 @@ class Theme
 public:
     Theme();
 
-    void saveToXmlFile(QIODevice *device);
+    void saveToXmlFile(QIODevice *device) const;
     QByteArray saveToXmlData() const;
     void loadFromXmlData(const QByteArray &data);
 
diff --git a/src/xlsx/xlsxworkbook.cpp b/src/xlsx/xlsxworkbook.cpp
index 9678f7a..631f790 100755
--- a/src/xlsx/xlsxworkbook.cpp
+++ b/src/xlsx/xlsxworkbook.cpp
@@ -395,9 +395,9 @@ void Workbook::prepareDrawings()
     }
 }
 
-void Workbook::saveToXmlFile(QIODevice *device)
+void Workbook::saveToXmlFile(QIODevice *device) const
 {
-    Q_D(Workbook);
+    Q_D(const Workbook);
     QXmlStreamWriter writer(device);
 
     writer.writeStartDocument(QStringLiteral("1.0"), true);
@@ -474,7 +474,7 @@ void Workbook::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-QByteArray Workbook::saveToXmlData()
+QByteArray Workbook::saveToXmlData() const
 {
     QByteArray data;
     QBuffer buffer(&data);
diff --git a/src/xlsx/xlsxworkbook.h b/src/xlsx/xlsxworkbook.h
index 5bd5ff5..14ac4a7 100755
--- a/src/xlsx/xlsxworkbook.h
+++ b/src/xlsx/xlsxworkbook.h
@@ -82,8 +82,8 @@ private:
 
     Workbook();
 
-    void saveToXmlFile(QIODevice *device);
-    QByteArray saveToXmlData();
+    void saveToXmlFile(QIODevice *device) const;
+    QByteArray saveToXmlData() const;
     bool loadFromXmlFile(QIODevice *device);
     bool loadFromXmlData(const QByteArray &data);
 
diff --git a/src/xlsx/xlsxworksheet.cpp b/src/xlsx/xlsxworksheet.cpp
index 42ba1af..7e4cf33 100755
--- a/src/xlsx/xlsxworksheet.cpp
+++ b/src/xlsx/xlsxworksheet.cpp
@@ -83,7 +83,7 @@ WorksheetPrivate::~WorksheetPrivate()
   makes comparing files easier. The span is the same for each
   block of 16 rows.
  */
-void WorksheetPrivate::calculateSpans()
+void WorksheetPrivate::calculateSpans() const
 {
     row_spans.clear();
     int span_min = XLSX_COLUMN_MAX+1;
@@ -132,7 +132,7 @@ void WorksheetPrivate::calculateSpans()
 }
 
 
-QString WorksheetPrivate::generateDimensionString()
+QString WorksheetPrivate::generateDimensionString() const
 {
     if (!dimension.isValid())
         return QStringLiteral("A1");
@@ -990,7 +990,7 @@ int Worksheet::writeHyperlink(int row, int column, const QUrl &url, const Format
     d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(displayString, Cell::String, fmt, this));
 
     //Store the hyperlink data in a separate table
-    d->urlTable[row][column] = new XlsxUrlData(XlsxUrlData::External, urlString, locationString, tip);
+    d->urlTable[row][column] = new XlsxHyperlinkData(XlsxHyperlinkData::External, urlString, locationString, tip);
 
     return error;
 }
@@ -1119,9 +1119,9 @@ int Worksheet::unmergeCells(const QString &range)
     return unmergeCells(CellRange(cell1.x(), cell1.y(), cell2.x(), cell2.y()));
 }
 
-void Worksheet::saveToXmlFile(QIODevice *device)
+void Worksheet::saveToXmlFile(QIODevice *device) const
 {
-    Q_D(Worksheet);
+    Q_D(const Worksheet);
     d->relationships.clear();
 
     QXmlStreamWriter writer(device);
@@ -1222,7 +1222,7 @@ void Worksheet::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
-void WorksheetPrivate::writeSheetData(QXmlStreamWriter &writer)
+void WorksheetPrivate::writeSheetData(QXmlStreamWriter &writer) const
 {
     calculateSpans();
     for (int row_num = dimension.firstRow(); row_num <= dimension.lastRow(); row_num++) {
@@ -1275,7 +1275,7 @@ void WorksheetPrivate::writeSheetData(QXmlStreamWriter &writer)
     }
 }
 
-void WorksheetPrivate::writeCellData(QXmlStreamWriter &writer, int row, int col, QSharedPointer<Cell> cell)
+void WorksheetPrivate::writeCellData(QXmlStreamWriter &writer, int row, int col, QSharedPointer<Cell> cell) const
 {
     //This is the innermost loop so efficiency is important.
     QString cell_pos = xl_rowcol_to_cell_fast(row, col);
@@ -1349,7 +1349,7 @@ void WorksheetPrivate::writeCellData(QXmlStreamWriter &writer, int row, int col,
     writer.writeEndElement(); //c
 }
 
-void WorksheetPrivate::writeMergeCells(QXmlStreamWriter &writer)
+void WorksheetPrivate::writeMergeCells(QXmlStreamWriter &writer) const
 {
     if (merges.isEmpty())
         return;
@@ -1367,7 +1367,7 @@ void WorksheetPrivate::writeMergeCells(QXmlStreamWriter &writer)
     writer.writeEndElement(); //mergeCells
 }
 
-void WorksheetPrivate::writeDataValidations(QXmlStreamWriter &writer)
+void WorksheetPrivate::writeDataValidations(QXmlStreamWriter &writer) const
 {
     if (dataValidationsList.isEmpty())
         return;
@@ -1381,25 +1381,25 @@ void WorksheetPrivate::writeDataValidations(QXmlStreamWriter &writer)
     writer.writeEndElement(); //dataValidations
 }
 
-void WorksheetPrivate::writeHyperlinks(QXmlStreamWriter &writer)
+void WorksheetPrivate::writeHyperlinks(QXmlStreamWriter &writer) const
 {
     if (urlTable.isEmpty())
         return;
 
     writer.writeStartElement(QStringLiteral("hyperlinks"));
-    QMapIterator<int, QMap<int, XlsxUrlData *> > it(urlTable);
+    QMapIterator<int, QMap<int, XlsxHyperlinkData *> > it(urlTable);
     while (it.hasNext()) {
         it.next();
         int row = it.key();
-        QMapIterator <int, XlsxUrlData *> it2(it.value());
+        QMapIterator <int, XlsxHyperlinkData *> it2(it.value());
         while (it2.hasNext()) {
             it2.next();
             int col = it2.key();
-            XlsxUrlData *data = it2.value();
+            XlsxHyperlinkData *data = it2.value();
             QString ref = xl_rowcol_to_cell(row, col);
             writer.writeEmptyElement(QStringLiteral("hyperlink"));
             writer.writeAttribute(QStringLiteral("ref"), ref);
-            if (data->linkType == XlsxUrlData::External) {
+            if (data->linkType == XlsxHyperlinkData::External) {
 
                 //Update relationships
                 relationships.addWorksheetRelationship(QStringLiteral("/hyperlink"), data->url, QStringLiteral("External"));
@@ -1423,7 +1423,7 @@ void WorksheetPrivate::writeHyperlinks(QXmlStreamWriter &writer)
     writer.writeEndElement();//hyperlinks
 }
 
-void WorksheetPrivate::writeDrawings(QXmlStreamWriter &writer)
+void WorksheetPrivate::writeDrawings(QXmlStreamWriter &writer) const
 {
     if (!drawing)
         return;
@@ -1732,7 +1732,7 @@ void Worksheet::prepareImage(int index, int image_id)
  height hasn't been set by the user we use the default value. If
  the row is hidden it has a value of zero.
 */
-int WorksheetPrivate::rowPixelsSize(int row)
+int WorksheetPrivate::rowPixelsSize(int row) const
 {
     double height;
     if (row_sizes.contains(row))
@@ -1748,7 +1748,7 @@ int WorksheetPrivate::rowPixelsSize(int row)
  by the user we use the default value. If the column is hidden it
  has a value of zero.
 */
-int WorksheetPrivate::colPixelsSize(int col)
+int WorksheetPrivate::colPixelsSize(int col) const
 {
     double max_digit_width = 7.0; //For Calabri 11
     double padding = 5.0;
@@ -1780,7 +1780,7 @@ int WorksheetPrivate::colPixelsSize(int col)
         x_abs         Absolute distance to left side of object.
         y_abs         Absolute distance to top side of object.
 */
-XlsxObjectPositionData WorksheetPrivate::objectPixelsPosition(int col_start, int row_start, double x1, double y1, double width, double height)
+XlsxObjectPositionData WorksheetPrivate::objectPixelsPosition(int col_start, int row_start, double x1, double y1, double width, double height) const
 {
     double x_abs = 0;
     double y_abs = 0;
@@ -1841,7 +1841,7 @@ XlsxObjectPositionData WorksheetPrivate::objectPixelsPosition(int col_start, int
         12,700 EMUs per point. Therefore, 12,700 * 3 /4 = 9,525 EMUs per
         pixel
 */
-XlsxObjectPositionData WorksheetPrivate::pixelsToEMUs(const XlsxObjectPositionData &data)
+XlsxObjectPositionData WorksheetPrivate::pixelsToEMUs(const XlsxObjectPositionData &data) const
 {
     XlsxObjectPositionData result = data;
     result.x1 = static_cast<int>(data.x1 * 9525 + 0.5);
@@ -1856,7 +1856,7 @@ XlsxObjectPositionData WorksheetPrivate::pixelsToEMUs(const XlsxObjectPositionDa
     return result;
 }
 
-QByteArray Worksheet::saveToXmlData()
+QByteArray Worksheet::saveToXmlData() const
 {
     QByteArray data;
     QBuffer buffer(&data);
diff --git a/src/xlsx/xlsxworksheet.h b/src/xlsx/xlsxworksheet.h
index e05928f..841921c 100755
--- a/src/xlsx/xlsxworksheet.h
+++ b/src/xlsx/xlsxworksheet.h
@@ -139,8 +139,8 @@ private:
     void setSheetName(const QString &sheetName);
     Relationships &relationships();
 
-    void saveToXmlFile(QIODevice *device);
-    QByteArray saveToXmlData();
+    void saveToXmlFile(QIODevice *device) const;
+    QByteArray saveToXmlData() const;
     bool loadFromXmlFile(QIODevice *device);
     bool loadFromXmlData(const QByteArray &data);
 
diff --git a/src/xlsx/xlsxworksheet_p.h b/src/xlsx/xlsxworksheet_p.h
index 6780af9..705afb3 100644
--- a/src/xlsx/xlsxworksheet_p.h
+++ b/src/xlsx/xlsxworksheet_p.h
@@ -57,7 +57,7 @@ const int XLSX_STRING_MAX = 32767;
 
 class SharedStrings;
 
-struct XlsxUrlData
+struct XlsxHyperlinkData
 {
     enum LinkType
     {
@@ -65,7 +65,7 @@ struct XlsxUrlData
         Internal
     };
 
-    XlsxUrlData(LinkType linkType=External, const QString &url=QString(), const QString &location=QString(), const QString &tip=QString()) :
+    XlsxHyperlinkData(LinkType linkType=External, const QString &url=QString(), const QString &location=QString(), const QString &tip=QString()) :
         linkType(linkType), url(url), location(location), tip(tip)
     {
 
@@ -180,20 +180,20 @@ public:
     ~WorksheetPrivate();
     int checkDimensions(int row, int col, bool ignore_row=false, bool ignore_col=false);
     Format cellFormat(int row, int col) const;
-    QString generateDimensionString();
-    void calculateSpans();
+    QString generateDimensionString() const;
+    void calculateSpans() const;
     void splitColsInfo(int colFirst, int colLast);
 
-    void writeSheetData(QXmlStreamWriter &writer);
-    void writeCellData(QXmlStreamWriter &writer, int row, int col, QSharedPointer<Cell> cell);
-    void writeMergeCells(QXmlStreamWriter &writer);
-    void writeHyperlinks(QXmlStreamWriter &writer);
-    void writeDrawings(QXmlStreamWriter &writer);
-    void writeDataValidations(QXmlStreamWriter &writer);
-    int rowPixelsSize(int row);
-    int colPixelsSize(int col);
-    XlsxObjectPositionData objectPixelsPosition(int col_start, int row_start, double x1, double y1, double width, double height);
-    XlsxObjectPositionData pixelsToEMUs(const XlsxObjectPositionData &data);
+    void writeSheetData(QXmlStreamWriter &writer) const;
+    void writeCellData(QXmlStreamWriter &writer, int row, int col, QSharedPointer<Cell> cell) const;
+    void writeMergeCells(QXmlStreamWriter &writer) const;
+    void writeHyperlinks(QXmlStreamWriter &writer) const;
+    void writeDrawings(QXmlStreamWriter &writer) const;
+    void writeDataValidations(QXmlStreamWriter &writer) const;
+    int rowPixelsSize(int row) const;
+    int colPixelsSize(int col) const;
+    XlsxObjectPositionData objectPixelsPosition(int col_start, int row_start, double x1, double y1, double width, double height) const;
+    XlsxObjectPositionData pixelsToEMUs(const XlsxObjectPositionData &data) const;
 
     QSharedPointer<Cell> readNumericCellData(QXmlStreamReader &reader);
     void readSheetData(QXmlStreamReader &reader);
@@ -210,7 +210,7 @@ public:
     Drawing *drawing;
     QMap<int, QMap<int, QSharedPointer<Cell> > > cellTable;
     QMap<int, QMap<int, QString> > comments;
-    QMap<int, QMap<int, XlsxUrlData *> > urlTable;
+    QMap<int, QMap<int, XlsxHyperlinkData *> > urlTable;
     QList<CellRange> merges;
     QList<XlsxImageData *> imageList;
     QMap<int, QSharedPointer<XlsxRowInfo> > rowsInfo;
@@ -224,7 +224,7 @@ public:
     CellRange dimension;
     int previous_row;
 
-    QMap<int, QString> row_spans;
+    mutable QMap<int, QString> row_spans;
     QMap<int, double> row_sizes;
     QMap<int, double> col_sizes;