Question

Xcode 7.1

我在Swift中创建一个简单的布局约束：

override func viewDidLoad()
{
    super.viewDidLoad()

    let search: UISearchBar = UISearchBar.init()

    let viewDict: = ["search" : search, "top" : topLayoutGuide]

    let con1 = NSLayoutConstraint.constraintsWithVisualFormat("H:|[search]|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: viewDict)
    let con2 = NSLayoutConstraint.constraintsWithVisualFormat("V:[top][search]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: viewDict)
    view.addConstraints(con1)
    view.addConstraints(con2)
}

此代码无法编译，您将获得：

“NSDictionary不能转换为[String：AnyObject]”

似乎viewDict的类型推断为NSDictionary。但是，以下推断为Dictionary：

let viewDict = ["search" : search]

并且代码编译。

我可以通过这样的显式输入来修复：

let viewDict: Dictionary<String, AnyObject> = ["search" : search, "top" : topLayoutGuide]

问题是：为什么添加topLayoutGuide会破坏类型推断？我原以为Swift语法[：]会产生Dictionary并且我必须使用

let test: NSDictionary = NSDictionary()
test.setValue("hello", forKey: "key1")

如果我想要NSDictionary

Swift 2.1中的NSDictionary vs Dictionary类型推断

0 个答案: