Why Invalidate() should be called outside the control then it can work ?

Question

I am using C# + winforms to develop software.
I have a UserControl which contains several DataGridView

datagridview1.datasource = from p in dc.doctor select p;

I use linq to sql to populate the dataGridView with dataSource, because I need to refresh the datasource to update the records, so I create a new dataContext and assign the datasource again.

datagridview1.datasource = from p in dc.doctor select p;  

At first I found, although I reset the datasource, the datagridview still can not get refreshed, someone tell me that I should call the invalidate function on datagridview, I tried. To a certain extent, it works. But If I called the Invalidate inside the UserControl's class, it won't work.
If I create a public function on the UserControl's class, then call it with userControl.refreshRecord(), Then it works.

Can someone point me what am I missed ? When someone call invalidate, when will it really work?
Thanks in advance !

Answer 1

Call dgv.Invalidate() method for datagridview.

Answer 2

Invalidate work when the control finish all other things like data loading ...