如何以编程方式在WPF DataGrid中选择行或单元格？

In WinForm DataGridView, it automatically selects the first row when initialized. It drove me crazy when I tried to turn that feature off. Moving to WPF DataGrid, it seems Microsoft has decided to turn this feature off, which is a good thing I think. However, I have hard time to enable this feature now. For some DataGrid, I want the first row to be selected automatically after grid is populated through data binding. There are some suggestions in Internet, but I couldn't make that work. I hope for better luck here. In WinForm DataGridView, it automatically selec