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[Source] NPOI Operation Excel Detailed Explanation

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Posted on 2021-5-16 21:04:14 | | | |
NPOI can read and write Word or Excel documents without Office installed. NPOI is an open-source C# project for reading and writing Microsoft OLE2 component documents such as Excel and WORD.
Review:

NPOI judgment of cell date type
https://www.itsvse.com/thread-9649-1-1.html

Import Pictures to Excel Sheets Using NPOI [with Source Code]
https://www.itsvse.com/thread-9477-1-1.html

NPOI sets the width and height of the cells
https://www.itsvse.com/thread-3522-1-1.html

. NPOI read and write operation Excel table plug-in for Net
https://www.itsvse.com/thread-2288-1-1.html

Assembly name
modules/namespaces
illustrate
NPOI.DLL
NPOI. POIFS
OLE2/ActiveX document attribute read/write library
NPOI.DLL
NPOI. DDF
Microsoft Office Drawing read/write library
NPOI.DLL
NPOI. HPSF
OLE2/ActiveX document read/write library
NPOI.DLL
NPOI. HSSF
Microsoft Excel BIFF (Excel 97-2003, doc) format read/write library
NPOI.DLL
NPOI. SS
Excel public interface and Excel formula calculation engine
NPOI.DLL
NPOI. Util
The basic library provides many useful functions for the development of other read/write file format projects
NPOI. OOXML.DLL
NPOI. XSSF
Excel 2007 (xlsx) format read and write library
NPOI. OOXML.DLL
NPOI. XWPF
Word 2007 (docx) format read/write library
NPOI. OpenXml4Net.DLL
NPOI. OpenXml4Net
OpenXml underlying zip package read and write library
NPOI. OpenXmlFormats.DLL
NPOI. OpenXmlFormats
Microsoft Office OpenXml object relationship library

HSSFWorkbook: is a version of Excel 2003 or earlier (including 2003) with a .xls extension
XSSFWorkbook: is the version of Excel 2007 with .xlsx extension
Automatically recognizes Excel versions

When reading excel, npoi calls WorkbookFactory.Create to automatically recognize the version:



Source code address:The hyperlink login is visible.



Implementation code:

XSSFWorkbook 2007 throws a Cannot access a closed Stream exception



Test code:



When exporting a file to a stream, calling the Write method throws an exception:



Unhandled exception. System.ObjectDisposedException: Cannot access a closed Stream.
   at System.IO.MemoryStream.Seek(Int64 offset, SeekOrigin loc)

HSSFWorkbook does not have this problem, and there is no way to overload the IWorkbook interface Write, as shown in the figure below:



ButThe XSSFWorkbook object will have an additional leaveOpen parameter, source code address:The hyperlink login is visible.



Solution 1:

Solution 2:

Create a new NpoiMemoryStream object and override the Close method as follows:

Use it as follows:

XSSFWorkbook CopySheet exception

When the sheet is my custom template, calling the CopySheet method will throw the following exception:

Object reference not set to an instance of an object.

Clone sheet using CloneSheet, the code is as follows:



(End)




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