自定义导航栏返回按钮标题

两个条件都满足
self.navigationController.navigationBar.topItem.title=@“”；


- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPushItem:(UINavigationItem *)item{
    
    UIBarButtonItem *back = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil];
    
    item.backBarButtonItem = back;
    
    return YES;
    
}