c# - Why does Microsoft.Office.Interop.Excel corrupts my excel file? -

i found lib on net

// library handle excel files in simple way. // copyright (c) 2009  gorka suárez garcía // // program free software: can redistribute and/or modify // under terms of gnu lesser general public license published // free software foundation, either version 3 of license, or // (at option) later version. // // program distributed in hope useful, // without warranty; without implied warranty of // merchantability or fitness particular purpose.  see // gnu lesser general public license more details. // // should have received copy of gnu lesser general public license // along program.  if not, see . using system; using system.collections.generic; using system.reflection; using microsoft.office.interop.excel;  namespace excel {     /// <summary>     /// class used handle excel file write , read it.     /// author: gorka suárez garcía     /// </summary>     public class excelhandler     {         /// <summary>         /// excel application instance.         /// </summary>         private applicationclass app;          /// <summary>         /// excel book.         /// </summary>         private workbook book;          /// <summary>         /// path of excel file.         /// </summary>         private string path;          /// <summary>         /// constructs new excelhandler object.         /// </summary>         public excelhandler()         {             this.app = null;             this.book = null;             this.path = null;         }          /// <summary>         /// destroys excelhandler object.         /// </summary>         ~excelhandler()         {             if (this.app != null)             {                 this.app.quit();             }         }          /// <summary>         /// opens excel file.         /// </summary>         /// <param name="path">the file open.</param>         public void open(string path)         {             this.path = path;              this.app = new applicationclass();             this.app.visible = true;             /*this.app.screenupdating = false;             this.app.displayalerts = false;*/              this.book = this.app.workbooks.open(this.path, missing.value, missing.value, missing.value,                                                 missing.value, missing.value, missing.value, missing.value,                                                 missing.value, missing.value, missing.value, missing.value,                                                 missing.value, missing.value, missing.value);              if (this.book == null)                 throw new exception("can't open excel book file.");         }          /// <summary>         /// writes value in cell.         /// </summary>         /// <param name="sheet">the sheet write.</param>         /// <param name="cell">the cell write.</param>         /// <param name="value">the value write.</param>         public void write(string sheet, string cell, string value)         {             worksheet wsheet = this.getsheet(sheet);             range range = wsheet.get_range(cell, cell);             range.value2 = value;         }          /// <summary>         /// reads value cell.         /// </summary>         /// <param name="sheet">the sheet read.</param>         /// <param name="cell">the cell read.</param>         /// <returns>the value cell.</returns>         public string read(string sheet, string cell)         {             worksheet wsheet = this.getsheet(sheet);             range range = wsheet.get_range(cell, cell);              if (range.value2 != null)                 return range.value2.tostring();             else                 return "";         }          /// <summary>         /// clears content of excel book.         /// </summary>         public void clear()         {             worksheet sheet = null;             (int = 1; <= this.book.worksheets.count; i++)             {                 sheet = (worksheet)this.book.worksheets[i];                 sheet.cells.clear();             }         }          /// <summary>         /// closes excel file.         /// </summary>         public void close()         {             this.book.saveas(this.path, xlfileformat.xlworkbooknormal, missing.value, missing.value,                              false, false, xlsaveasaccessmode.xlshared, false, false, missing.value,                              missing.value, missing.value);             this.book.close(true, missing.value, missing.value);             this.app.quit();              this.app = null;             this.book = null;             this.path = null;         }          /// <summary>         /// gets names of sheets inside excel book.         /// </summary>         /// <returns>a list of sheets names.</returns>         public string[] getsheetsnames()         {             list<string> names = new list<string>();             worksheet sheet = null;              (int = 1; <= this.book.worksheets.count; i++)             {                 sheet = (worksheet)this.book.worksheets[i];                 names.add(sheet.name);             }              return names.toarray();         }          /// <summary>         /// gets sheet we're looking for.         /// </summary>         /// <param name="name">the name of sheet.</param>         /// <returns>the sheet we're looking for.</returns>         protected worksheet getsheet(string name)         {             int index = this.getsheetindex(name);             if (index == 0)                 throw new exception("invalid sheet name.");              worksheet sheet = (worksheet)this.book.worksheets[index];             return sheet;         }          /// <summary>         /// gets index of sheet we're looking for.         /// </summary>         /// <param name="name">the name of sheet.</param>         /// <returns>the index of sheet we're looking for.</returns>         protected int getsheetindex(string name)         {             worksheet sheet = null;             (int = 1; <= this.book.worksheets.count; i++)             {                 sheet = (worksheet)this.book.worksheets[i];                 if (sheet.name == name) return i;             }             return 0;         }     } } 

and i'm trying use fill template made in excel. example:

excel.excelhandler handler = new excel.excelhandler(); handler.open(this.filename); handler.write("informe", "e9", row.fecha); handler.close(); 

it works okay... no errors... when try open filled xlsx, excel says it's corrupt. ideas why??? i'm losing mind on this, apreciated.

regards.

try change xlfileformat.xlworkbooknormal xlfileformat.xlworkbookdefault or xlopenxmlworkbook. looks file saved in 'xls' format 'xlsx' extension. hence error.