Excel Interop Example
This page was last reviewed on May 22, 2023.
Dot Net Perls
Excel. This application creates XLS and XLSX files. These files are hard to read in C# programs. They are handled with the Microsoft.Office.Interop.Excel assembly.
This assembly sometimes creates performance issues. Step-by-step instructions are helpful. Excel interop is difficult, but with some care we can make it usable.
First example. We must include a namespace to use Excel in your C# program. We need to add an assembly to your program to use Excel interop—use the Add Reference command for this.
Tip Add the Microsoft.Office.Interop.Excel assembly by going to Project, then Add Reference.
Start We make a new C# class file in Visual Studio and you can call it something like ExcelInterop.
Info If you look at Excel interop objects in IntelliSense, you will see many functions. You will only need to use a few.
/// <summary> /// This class contains the Excel Interop code we need. /// It can be shared in many places to avoid duplication. /// </summary> class ExcelReaderInterop { /// <summary> /// Store the Application object we can use in the member functions. /// </summary> Application _excelApp; /// <summary> /// Initialize a new Excel reader. Must be integrated /// with an Excel interface object. /// </summary> public ExcelReaderInterop() { _excelApp = new Application(); } }
Interop class. This class stores our Excel information. Put an Application object called _excelApp as a member. In the constructor, make the _excelApp a new Application object.
Detail Put a public function on the class, and it can use the _excelApp we already have. This code uses the Workbooks.Open method.
Next Open a workbook with Workbooks.Open. Send the workbook we open to another function called ExcelScanInternal.
Finally Close the workbook and release all the memory. You will need to deal with exceptions in the catch block.
Note I do not have the information about all the detailed exceptions that can be thrown. Just catch them in one statement.
/// <summary> /// Open the file path received in Excel. Then, open the workbook /// within the file. Send the workbook to the next function, the internal scan /// function. Will throw an exception if a file cannot be found or opened. /// </summary> public void ExcelOpenSpreadsheets(string thisFileName) { try { // // This mess of code opens an Excel workbook. I don't know what all // those arguments do, but they can be changed to influence behavior. // Workbook workBook = _excelApp.Workbooks.Open(thisFileName, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing); // // Pass the workbook to a separate function. This new function // will iterate through the worksheets in the workbook. // ExcelScanInternal(workBook); // // Clean up. // workBook.Close(false, thisFileName, null); Marshal.ReleaseComObject(workBook); } catch { // // Deal with exceptions. // } }
Loop. To get data from workbooks, you will need to loop over the sheets. An Excel workbook has one or more sheets. In Excel, you can switch between sheets by clicking on the tabs on the bottom.
Tip In Excel Interop, sheets are indexed starting at 1. This is similar to Visual Basic but not the C# language.
Detail The object array is directly usable in the C# language. Once you get the objects, you don't need to do any more Interop.
And This provides a huge performance boost. There are benefits to reducing calls to Excel Interop.
/// <summary> /// Scan the selected Excel workbook and store the information in the cells /// for this workbook in an object[,] array. Then, call another method /// to process the data. /// </summary> private void ExcelScanInternal(Workbook workBookIn) { // // Get sheet Count and store the number of sheets. // int numSheets = workBookIn.Sheets.Count; // // Iterate through the sheets. They are indexed starting at 1. // for (int sheetNum = 1; sheetNum < numSheets + 1; sheetNum++) { Worksheet sheet = (Worksheet)workBookIn.Sheets[sheetNum]; // // Take the used range of the sheet. Finally, get an object array of all // of the cells in the sheet (their values). You can do things with those // values. See notes about compatibility. // Range excelRange = sheet.UsedRange; object[,] valueArray = (object[,])excelRange.get_Value( XlRangeValueDataType.xlRangeValueDefault); // // Do something with the data in the array with a custom method. // ProcessObjects(valueArray); } }
Performance. There are possible performance issues with Excel interop. The Cells indexer on a range, or getting the range with the Range property can be slow.
Note This document is based on .NET 3.5. The approach shown here is the fastest one.
Warning If you do your Excel processing wrong, you could be waiting a long time to process even 10 spreadsheets at once.
Cells[]: 30.0 seconds get_Range(), Cells[]: 15.0 seconds UsedRange, get_Value(): 1.5 seconds [fastest]
Charts. It is possible to create charts directly in your Excel workbooks. The ChartWizard method is useful for this. We use the ChartObjects property and Add a Chart.
Info The range of the data we want to chart is encoded in the topLeft and bottomRight constants.
Next We set the range of the chart with SetSourceData. We use the XlChartType.xlLine enumerated constant and call ChartWizard().
Tip Include the Microsoft.Office.Interop.Excel namespace by right-clicking on References and selecting Add Reference.
using Microsoft.Office.Interop.Excel; class Program { const string fileName = "C:\\Book1.xlsx"; const string topLeft = "A1"; const string bottomRight = "A4"; const string graphTitle = "Graph Title"; const string xAxis = "Time"; const string yAxis = "Value"; static void Main() { // Open Excel and get first worksheet. var application = new Application(); var workbook = application.Workbooks.Open(fileName); var worksheet = workbook.Worksheets[1] as Microsoft.Office.Interop.Excel.Worksheet; // Add chart. var charts = worksheet.ChartObjects() as Microsoft.Office.Interop.Excel.ChartObjects; var chartObject = charts.Add(60, 10, 300, 300) as Microsoft.Office.Interop.Excel.ChartObject; var chart = chartObject.Chart; // Set chart range. var range = worksheet.get_Range(topLeft, bottomRight); chart.SetSourceData(range); // Set chart properties. chart.ChartType = Microsoft.Office.Interop.Excel.XlChartType.xlLine; chart.ChartWizard(Source: range, Title: graphTitle, CategoryTitle: xAxis, ValueTitle: yAxis); // Save. workbook.Save(); } }
The program requires an Excel document named Book1.xlsx located at C:\Book1.xlsx. In this file, you need to add 4 values in the first column.
And The program will create a chart based on those 4 values. Many options can be changed to create different charts.
Compatibility. There is a compatibility issue with the Excel program on the macOS platform. Excel stores OA dates in different formats on Macs and PCs.
Important The function get_Value() returns objects that do not vary based on the original platform.
We used Excel interop and avoided performance problems. It is confusing to call the complicated Open method with Type.Missing in more places than necessary.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on May 22, 2023 (edit).
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