动态创建的datagridview列不可访问,除非添加到窗体中…为什么?

引发错误的代码:

DataGridView gv = new DataGridView();
gv.DataSource = GetDataTable(); //binding it to datatable
Debug.Assert(gv.Columns == null);

DataGridView gv = new DataGridView();
gv.DataSource = GetDataTable(); //binding it to datatable
this.Controls.Add(gv); //adding to form
Debug.Assert(gv.Columns == null); //the assertion fails!

为什么这种行为如此?有解决办法吗?