ios设置返回按钮为图片

//设置导航条上面的闹钟选项-(void) setClockItem {//设置导航条右侧按钮UIButton*rightButton = [[UIButton alloc]initWithFrame:CGRectMake(0,0,30,30)];    [rightButton setImage:[UIImage imageNamed:@"clock"] forState:UIControlStateNormal];    [rightButton addTarget:self action:@selector(returnMoneyClickBtn) forControlEvents:UIControlEventTouchUpInside];UIBarButtonItem*rightItem = [[UIBarButtonItem alloc]initWithCustomView:rightButton];self.navigationItem.rightBarButtonItem= rightItem;}