private void instanceViewPanel_DragOver(object sender, DragEventArgs e)
{
e.Effect = DragDropEffects.None;
// check type of the drag
if (e.Data.GetDataPresent(DataFormats.StringFormat))
{
string str = (string)e.Data.GetData(
DataFormats.StringFormat);
if(str.Contains(".type"))
e.Effect = DragDropEffects.All;
}
}