Sheet Lazy Loading Implementation

benchmarks/NPOI.Benchmarks/AssemblyInfo.cs

@@ -0,0 +1,17 @@
+using System.Runtime.InteropServices;
+
+// In SDK-style projects such as this one, several assembly attributes that were historically
+// defined in this file are now automatically added during build and populated with
+// values defined in project properties. For details of which attributes are included
+// and how to customise this process see: https://aka.ms/assembly-info-properties
+
+
+// Setting ComVisible to false makes the types in this assembly not visible to COM
+// components.  If you need to access a type in this assembly from COM, set the ComVisible
+// attribute to true on that type.
+
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM.
+
+[assembly: Guid("e468bef5-fc11-425b-a4a3-0ee201802090")]

benchmarks/NPOI.Benchmarks/LargeExcelFileBenchmark.cs

@@ -42,8 +42,18 @@ public void GlobalSetup()
     }
 
     [Benchmark]
-    public void XSSFWorkbookLoad()
+    public void XSSFWorkbookLoad_DisableSheetLazyLoading()
     {
+        XSSFSheet.EnableLazyLoading = false;
+        var workbook = new XSSFWorkbook(_filePath, true);
+        workbook.Dispose();
+    }
+
+
+    [Benchmark]
+    public void XSSFWorkbookLoad_EnableSheetLazyLoading()
+    {
+        XSSFSheet.EnableLazyLoading = true;
         var workbook = new XSSFWorkbook(_filePath, true);
         workbook.Dispose();
     }

benchmarks/NPOI.Benchmarks/NPOI.Benchmarks.csproj

@@ -5,6 +5,8 @@
         <TargetFramework>net8.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <NoWarn>$(NoWarn);SYSLIB0014</NoWarn>
+        <SignAssembly>True</SignAssembly>
+        <AssemblyOriginatorKeyFile>..\..\npoi.snk</AssemblyOriginatorKeyFile>
     </PropertyGroup>
 
     <ItemGroup>

ooxml/Properties/AssemblyInfo.cs

@@ -1,6 +1,7 @@
 using System.Runtime.CompilerServices;
 using System.Security;
 
+[assembly: InternalsVisibleTo("NPOI.Benchmarks, PublicKey=002400000480000094000000060200000024000052534131000400000100010095ccd95af3b39d8bc20544d3f47fd24b53ebc5ccb693eaed116290629f8cd882c827ebd511ad59449224f0718d3f9d03b64945a6c8b6644266001b8c8426185330e3d96da70ae16d4acc21b8d4d480f1385c7e924273179375aa88f81380a72fb115712a313379d16aed4aa36208ee3b4a5dd785b06a07b2d868e3227f4495b5", AllInternalsVisible = true)] 
 [assembly: InternalsVisibleTo("NPOI.OOXML.TestCases, PublicKey=002400000480000094000000060200000024000052534131000400000100010095ccd95af3b39d8bc20544d3f47fd24b53ebc5ccb693eaed116290629f8cd882c827ebd511ad59449224f0718d3f9d03b64945a6c8b6644266001b8c8426185330e3d96da70ae16d4acc21b8d4d480f1385c7e924273179375aa88f81380a72fb115712a313379d16aed4aa36208ee3b4a5dd785b06a07b2d868e3227f4495b5", AllInternalsVisible = true)]
 #if NETSTANDARD2_1 || NET6_0_OR_GREATER || NETSTANDARD2_0 || NET40
 [assembly: AllowPartiallyTrustedCallers]

ooxml/XSSF/UserModel/XSSFChartSheet.cs

@@ -18,12 +18,9 @@ limitations under the License.
 using NPOI.OpenXmlFormats.Spreadsheet;
 using System.IO;
 using System.Xml;
-using System.Collections.Generic;
 using System;
-using NPOI.OpenXmlFormats;
 using NPOI.Util;
 using NPOI.OpenXml4Net.OPC;
-using NPOI.OpenXmlFormats.Dml;
 
 namespace NPOI.XSSF.UserModel
 {
@@ -80,25 +77,29 @@ internal override void Read(Stream is1)
          */
         public CT_Chartsheet GetCTChartsheet()
         {
+            EnsureWorksheetLoaded();
             return chartsheet;
         }
 
 
         protected override NPOI.OpenXmlFormats.Spreadsheet.CT_Drawing GetCTDrawing()
         {
+            EnsureWorksheetLoaded();
             return chartsheet.drawing;
         }
 
 
         protected override NPOI.OpenXmlFormats.Spreadsheet.CT_LegacyDrawing GetCTLegacyDrawing()
         {
+            EnsureWorksheetLoaded();
             return chartsheet.legacyDrawing;
         }
 
 
-        internal override void Write(Stream out1, bool leaveOpen=false)
+        internal override void Write(Stream output, bool leaveOpen=false)
         {
-            new ChartsheetDocument(this.chartsheet).Save(out1);
+            EnsureWorksheetLoaded();
+            new ChartsheetDocument(this.chartsheet).Save(output);
         }
 
         private static byte[] blankWorksheet()