UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithTitle:@"返回上级界面" style:UIBarButtonItemStylePlain target:nil action:nil];
self.navigationItem.backBarButtonItem = backItem;
UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"箭头left40x40"] style:UIBarButtonItemStylePlain target:nil action:nil];
self.navigationItem.backBarButtonItem = backItem;
