Question

当我输入特定的类时，函数是否可以返回特定的对象。我的问题：我不知道如何归还物体。看一下代码，谢谢

class MyViewControler { }

class MySplitViewController: NSSplitViewControler {
    override func viewDidLoad() {
        /* 
         * get specific object 
         */
        let vc = viewController(for: MyViewControler.self)
    }
}

extension NSSplitViewController {

    public func viewController<T>(for anClass: T) -> T.object {

        guard let tClass = anClass as? AnyClass else { return nil }
        var vc: NSViewController?
        if let idx = self.splitViewItems.index(where: { $0.viewController.classForCoder == tClass} ) {
            vc = self.splitViewItems[idx].viewController
        }
    }
    /*
     * I don't know how to return a specific object 
     */
    return vc
}

Answer 1

采取类型并返回的方法的签名（可选）该类型的实例将是：

public func viewController<T>(for aClass: T.Type) -> T?

或者，如果您想将其限制为NSViewController的子类：

public func viewController<T: NSViewController>(for aClass: T.Type) -> T?

使用可选绑定可以简化实现：

extension NSSplitViewController {
    public func viewController<T: NSViewController>(for aClass: T.Type) -> T? {
        for item in self.splitViewItems {
            if let vc = item.viewController as? T {
                return vc
            }
        }
        return nil
    }
}

或者作为“一线”：

extension NSSplitViewController {
    public func viewController<T: NSViewController>(for aClass: T.Type) -> T? {
        return self.splitViewItems.lazy.flatMap { $0.viewController as? T }.first
    }
}

如何使用Generic作为参数并返回特定对象而不进行强制转换？

1 个答案: