Swift项目中调用闭包问题

[KellyCoder]

Swift项目中调用以下闭包 QMUIThemeManagerCenter.defaultThemeManager.identifierForTrait = { (trait) -> (NSObject) in

                return "" as NSObject
            }

会包此错误 Cannot assign value of type '(UITraitCollection) -> (NSObject)' to type '((UITraitCollection) -> NSCopying & NSObjectProtocol)?' 怎么调用方式才是正确的呢？

[jiasongs]

错误提示很明显 返回一个 NSCopying & NSObjectProtocol) 即： QMUIThemeManagerCenter.defaultThemeManager.identifierForTrait = { (trait) -> (NSCopying & NSObjectProtocol) in return "" as NSString }

[sunimp]

return "" as NSString