private void comboBox1_DragDrop(object sender, DragEventArgs e)
{
string[] names = (string[]) e.Data.GetData(DataFormats.FileDrop);
comboBox1.Items.AddRange(names);
}
private void comboBox1_DragEnter(object sender, DragEventArgs e)
{
if(e.Data.GetDataPresent(DataFormats.FileDrop))
e.Effect = DragDropEffects.Copy;
}
Should give you the basic idea, the key is to handle the DragEnter and state what effect should be displayed, if this step is missed then the drop event will never be fired.