List of lists excel export

Strategically, you are doing it correctly. As Joe says, it is massively faster to execute cell value assignments by passing an entire array of values in one shot rather than by looping through the cells one by one.

Excel is COM based and so operates with Excel via the .NET interop. The interop is ignorant of generics, unfortunately, so you cannot pass it a List<T> or the like. A two dimensional array really is the only way to go.

That said, there are a few ways to clean up your code to make it a bit more manageable. Here are some thoughts:

(1) If you are using .NET 3.0, you can use LINQ to shorten your code from:

int numberOfColumns = int.MinValue;

foreach (List<object> outputColumns in outputRows)
{
        if (numberOfColumns < outputColumns.Count)
        { numberOfColumns = outputColumns.Count; }
}

to a single line:

int numberOfColumns = outputRows.Max(list => list.Count);

(2) Don’t use the _Worksheet or _Workbook interfaces. Make use of Worksheet or Workbook instead. See here for a discussion: Excel interop: _Worksheet or Worksheet?.

(3) Consider making use of the Range.Resize method, which comes through as Range.get_Resize in C#. This is a toss-up though — I actually like the way you are setting your range size. But it’s something that I thought that you might want to know about. For example, your line here:

Excel.Range oRng = oSheet.get_Range("A1", oSheet.Cells[numberOfRows,numberOfColumns]);

Could be changed to:

Excel.Range oRng = 
    oSheet.get_Range("A1", Type.Missing)
        .get_Resize(numberOfRows, numberOfColumns);

(4) You do not have to set the Application.UserControl to true. Making Excel visible to the user is enough. The UserControl property is not doing what you think it does. (See the help files here) If you want to control whether the user can control Excel or not, you should utilze Worksheet protection, or you could set Application.Interactive = false if you want to lock out your users. (Rarely a good idea.) But if you want to allow the user to use Excel, then simply making it visible is enough.

Overall, with these in mind, I think that your code could look something like this:

object oOpt = System.Reflection.Missing.Value; //for optional arguments
Excel.Application oXL = new Excel.Application();
Excel.Workbooks oWBs = oXL.Workbooks;
Excel.Workbook oWB = oWBs.Add(Excel.XlWBATemplate.xlWBATWorksheet);
Excel.Worksheet oSheet = (Excel.Worksheet)oWB.ActiveSheet;

//outputRows is a List<List<object>>
int numberOfRows = outputRows.Count;
int numberOfColumns = outputRows.Max(list => list.Count);

Excel.Range oRng = 
    oSheet.get_Range("A1", oOpt)
        .get_Resize(numberOfRows, numberOfColumns);

object[,] outputArray = new object[numberOfRows, numberOfColumns];

for (int row = 0; row < numberOfRows; row++)
{
    for (int col = 0; col < outputRows[row].Count; col++)
    {
        outputArray[row, col] = outputRows[row][col];
    }
}

oRng.set_Value(oOpt, outputArray);

oXL.Visible = true;

Hope this helps…

Mike

You can export to either:

• 
  Excel workbook    The data has a one-way connection to the original list. Periodically refreshing the workbook pulls in changes that have been made in the list.

• CSV (comma-separated values)file    It can be opened in Notepad or Excel. The data is not connected to the original list. (On macOS, exporting to CSV is the only available option.)

  Important: 

  • The maximum number of rows you can export to a CSV file is 30,000.

  • You might have noticed ‘Export to CSV’ option enabled on document libraries for a brief period. The option was enabled unintentionally so we had to disable it. We would love to bring the capability to document libraries, and we are working on it but do not have any time estimate that can be shared.

1. From the command bar of the SharePoint list, select Export to Excel  .

   Important: 
   Export to Excel is available only when list items are not selected.

   The classic SharePoint experience shows a ribbon above the list, not a command bar. Select the List tab on the ribbon, and then select Export to Excel.

   

   Depending on your browser, you can save and open, or open the file directly.

   Note: If you save the file, the default file name for the first copy is query.iqy, and it is placed in the default download folder for your browser. To change the name and location, use your browser’s Save as.

2. If needed, select OK > Open after the file download begins.

3. If prompted and you trust the SharePoint site, in the Excel security page, select Enable.

4. In the Excel Import Data dialog box, select the How you want to view this data and Where do you want to put the data options.

   

5. When done, select OK. The list should appear in Excel.

   

Excel creates an Excel table with a one-way data connection based on a web query file. To bring a fresh copy of the SharePoint list to Excel, select Refresh All on the Data tab. Changes made to the Excel table will not be sent to the SharePoint list.

If your SharePoint list contains folders, the folder structure does not appear in the resulting Excel table. However, the Item Type and Path columns are added to the Excel table so you can filter and sort the data, based on its type and location or subfolder of the list.