UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 60, 40)];
    [btn setImage:imageWhite forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(bpBack) forControlEvents:UIControlEventTouchUpInside];
    btn.backgroundColor = [UIColor greenColor];
    UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithCustomView:btn];
    leftItem.width = 60;
    self.navigationItem.leftBarButtonItem = leftItem;

... 
...
 btn.backgroundColor = [UIColor greenColor];
 if (@available(iOS 11.0,*)) {
     [btn setContentMode:UIViewContentModeScaleToFill];
     [btn setContentEdgeInsets:UIEdgeInsetsMake(0, 5, 5, 20)];
  }
 UIBarButtonItem *leftItem = [[UIBarButtonItem alloc] initWithCustomView:btn];
...
...

  CGRect frame = CGRectMake(0, 0, 150, 44);
  UISearchBar *search = [[UISearchBar alloc] initWithFrame:frame];
  search.placeholder = @"搜索";
  search.delegate = self;
  UITextField *searchField=[search valueForKey:@"_searchField"];
  searchField.backgroundColor = [UIColor groupTableViewBackgroundColor];
// --- iOS 11异常处理
  if(@available(iOS 11.0, *)) {
    [[search.heightAnchor constraintEqualToConstant:44] setActive:YES];
  }
  self.navigationItem.titleView = search;