How to: Sort items of a DataGrid

Question

How to: Sort items of a DataGrid using C# / WPF

I do have the following code snippets (unimportant code has been removed):

C#:

lastName.SortDirection = ListSortDirection.Ascending;

XAML:

<DataGrid AutoGenerateColumns="False" Name="dataGrid_Content">
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding lastName}" Header="Nachname" x:Name="lastName" />
    </DataGrid.Columns>
</DataGrid>

Unfortunately, the C# code is ignored - there is no ascending sorting, it only creates that little arrow which shows up, but the items are not sorted. What is my mistake?

Edit I:

public void SetItemsToDataContext()
    {
        dataGrid_Content.Items.Clear();

        foreach (string s in Directory.GetFiles(@"C:\Users\...", "*.txt"))
        {
            StreamReader streamReader = new StreamReader(s);

            int i = 1;
            string line = streamReader.ReadToEnd().Replace("\n", "");
            string[] t = line.Split('\r');

            BusinessContact businessContact = new BusinessContact();
            businessContact.firstName = t[i + 2];
            businessContact.lastName = t[i + 3];

            dataGrid_Content.Items.Add(businessContact);

            streamReader.Close();
        }

        applySortDescriptions(lastName, ListSortDirection.Ascending);
    }

Edit II:

public string getSortPropertyName(DataGridColumn col)
{
    return "Content";
}

Answer 1

Well, there is a way to get it working properly. Here it is.

    private void applySortDescriptions(DataGridColumn col, ListSortDirection listSortDirection)
    {
        //Clear current sort descriptions
        MyDataGrid.Items.SortDescriptions.Clear();

        //Get property name to apply sort based on desired column
        string propertyName = getSortPropertyName(col);           

        //Add the new sort description
        MyDataGrid.Items.SortDescriptions.Add(new SortDescription(propertyName, listSortDirection));

        //apply sort
        applySortDirection(col, listSortDirection);           

        //refresh items to display sort
        MyDataGrid.Items.Refresh();
    }

    private string getSortPropertyName(DataGridColumn col)
    {
        //place logic in here that will return the name of the property to sort by (ex: return “name”; if you are sorting by the name property)

        return string.Empty;
    }

    private void applySortDirection(DataGridColumn col, ListSortDirection listSortDirection)
    {
        foreach (DataGridColumn c in PatientsViewDatGrid.Columns)
        {
            c.SortDirection = null;
        }
        col.SortDirection = listSortDirection;
    }

That should do it. Now you can sort and the column headers will show the sort indicator appropriately