我试图在单击UIButton时显示UIPopoverController。这是我的代码:-(IBAction)showColumnChooser:(id)sender{ColumnChooserTVC*vc=[[ColumnChooserTVCalloc]init];[vcsetSelections:allColumns];[vcsetDelegate:self];UIPopoverController*pc=[[UIPopoverControlleralloc]initWithContentViewController:vc];[pcpresentPopoverFromRect:[s