DataGrid-Column widths not updating on ItemsSource change

Question

XAML:

Answer 1

For everyone's convenience, here is an extension method based on David's answer:

public static void AutoResizeColumnWidths(this System.Windows.Controls.DataGrid dataGrid)
{
    // http://stackoverflow.com/questions/4725724/wpf-datagrid-column-widths-not-updating-on-itemssource-change
    foreach (var column in dataGrid.Columns)
        column.Width = 0;

    dataGrid.UpdateLayout();

    foreach (var column in dataGrid.Columns)
        column.Width = System.Windows.Controls.DataGridLength.Auto;

    dataGrid.UpdateLayout();
}

And how it would be called:

dataGrid.AutoResizeColumnWidths();