//添加返回按钮
-(void)backBtn{
  UIButton *backBtn=[[UIButton alloc]initWithFrame:CGRectMake(0, 10, 60, 20)];
  [backBtn setTitle:@"返回" forState:UIControlStateNormal];
  backBtn.titleLabel.font=[UIFont systemFontOfSize:12];
  backBtn.imageEdgeInsets=UIEdgeInsetsMake(2,2,2,2);
  [backBtn setImage:[UIImage imageNamed:@"fanhui"] forState:UIControlStateNormal];
  [backBtn addTarget:self action:@selector(backto) forControlEvents:UIControlEventTouchDown];
  UIBarButtonItem *leftBtn=[[UIBarButtonItem alloc]initWithCustomView:backBtn];
  UIBarButtonItem *flexBtn=[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
  flexBtn.width=-10;//正数往左移，负数往右移
  self.navigationItem.leftBarButtonItems=@[flexBtn,leftBtn];
}
//返回按钮
-(void)backto{
  [self dismissViewControllerAnimated:YES completion:^{
  }];
}