刷新app输入前台的视图控制器内容

I have an app with a tab bar that has a few tabs with user-generated content. When each view controller loads, the viewDidLoad method makes HTTP requests to a server to fetch data, then populates its view correspondingly. Once all the data is loaded, however, the view remains the same (unless the view controller is unloaded and reloaded).I have an app with a tab bar that has a few tab