super.viewDidLoad() let urlString: String if navigationController?.tabBarItem.tag == 0 { urlString = "https://api.whitehouse.gov/v1/petitions.json?limit=100" } else { urlString = "https://api.whitehouse.gov/v1/petitions.json?signatureCountFloor=10000&limit=100" } if let url = URL(string: urlString) { if let data = try? Data(contentsOf: url) { parse(json: data) return } } navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .action, target: self, action: #selector(actionButton))
如果我在代码段之后创建
rightBarButton
(如上),则不会显示条形按钮。但是,如果在代码之前创建了rightBarButton
,则会出现rightBarButton
。我在导航控制器和标签栏控制器中嵌入了tableViewController
。为什么在代码后显示按钮不显示按钮?
super.viewDidLoad()让urlString:如果navigationController?.tabBarItem.tag == 0 {urlString =“ https://api.whitehouse.gov/v1/petitions.json?limit=100”}的其他字符串{urlString = “ https:// api ....
删除return
关键字,return
将不再执行代码的其他行。请参阅confused with the functionality of return
in swift的答案。