Operation is not valid while ItemCollection has no inner collection.

I got a user control 'SubForm'

When click a button on the main form, the 'SubForm' will be added and default data will load to the grid

		SubForm subform = new SubForm();
                grid_SubForm.Children.Add(subform);
		subform.Visibility = Visibility.Visible;
		subform.LoadDataToGrid(); 

Then I got error in LoadDataGrid()

This is function in 'SubForm' to load data in Data Grid as default

dataGrid_grid1's source and header information is set dynamically on User Control Loaded function.

     (subform.dataGrid_grid1.Items[row] as DataRowView).Row[column] = 1;

'Operation is not valid while ItemCollection has no inner collection. ItemCollection is uninitialized or binding on ItemsControl.ItemSource supplied null for collection.'

Any solution? thanks.