Question

I have a List<List<string>> where the outer list will be the rows for a grid and the inner list the column values.

How can I wrap the List<List<string>> so it’s a suitable DataSource for the grid, which accepts IList or IBindingList?

Effectively I want it to be seen as a List<MyObject> with the MyObject class having exposing the strings as public properties for binding.

I can’t change the list and it can have a very big number of rows so copying the data wouldn’t be ideal.

A simple example of the difference is the following code with a DataGridView dropped on a WinForm:

 public class SupplierEntry
    {
        public string SupplierCode
        {
            get
            {
                return "SUPPLIERCODE";
            }
        }

        public string SupplierTitle
        {
            get
            {
                return "SUPPLIERTITLE";
            }
        }
    }

    private void Test()
    {
        List<string> supplierEntryString = new List<string>();
        supplierEntryString.Add("SUPPLIERCODE");
        supplierEntryString.Add("SUPPLIERTITLE");            

        List<List<string>> supplierListStrings = new List<List<string>>();
        supplierListStrings.Add(supplierEntryString);

        List<SupplierEntry> supplierListObjects = new List<SupplierEntry>();

        SupplierEntry supplierEntryObject = new SupplierEntry();
        supplierListObjects.Add(supplierEntryObject);

        //this can't handle the nested collections, instead showing a Capacity and Count column 
        dataGridView1.DataSource = supplierListStrings;

        //this works giving you a supplier code and title column
        //dataGridView1.DataSource = supplierListObjects;
    }

Answer 1

When setting the DataSource of a DataGridView, the DataGridView will treat the supplied object as an IList<something>, where for each something it will use reflection to find all the public readable properties. The public readable properties of a List<string> are Capacity and Count.

In order to get your strings to appear in the DataGridView they must be presented as properties. You can do this at least three ways: Make your own class (as you have already done with SupplierEntry), use a Tuple, or use an anonymous type.

A compromise that would allow you to use your source List<List<string>> without copying any data would be to provide a wrapper class which just presents the data as properties:

// Provide named properties which really just read elements 
// from the List<string> provided with the constructor
public class ListBasedRecord {
    public string SupplierName { get { return source[0]; } }
    public string SupplierCode { get { return source[1]; } }
    private List<string> source;
    public ListBasedRecord(List<string> source) { this.source = source; }
}

private void ListTest() {
    // ... same as above, you get your List<List<string>> ...
    // Succinctly create a SupplierEntryWrapper for each "record" in the source
    var wrapperList = supplierListStrings
                      .Select(x => new SupplierEntryWrapper(x)).ToList();
    dataGridView1.DataSource = wrapperList;
}