向所有uiviewcontroller添加变量

我对斯威夫特不熟悉,我正在努力实现一个习惯 UIKeyCommand 实践应用程序中的体系结构。我在下面为基地写了扩展名 UISplitViewController 全部显示 UIKeyCommands 在屏幕上的当前视图中。

extension UISplitViewController {
    open override var canBecomeFirstResponder: Bool {
        return true
    }

    var BPKeyCommands: [BPKeyCommand]? {
        var commands: [BPKeyCommand] = []

        var mastervc = self.viewControllers.first
        if (mastervc is UINavigationController) {
            mastervc = (mastervc as! UINavigationController).viewControllers.last
        }
        if let masterCommands = mastervc.commands {
            for command in masterCommands {
                commands.append(command)
            }
        }

        return commands
    }

    open override var keyCommands: [UIKeyCommand]? {
        var commands: [UIKeyCommand] = []

        if let bpkeycommands = BPKeyCommands {
            for command in bpkeycommands {
                let new = UIKeyCommand(input: command.input,
                                       modifierFlags: command.modifierFlags,
                                       action: #selector(executeKeyCommand(sender:)),
                                       discoverabilityTitle: command.title)
                commands.append(new)
            }
        }

        return commands
    }

    @objc private func executeKeyCommand(sender: UIKeyCommand) {
        if let index = keyCommands?.firstIndex(of: sender) {
            if let command = BPKeyCommands?[index] {
                command.action(command)
            }
        }
    }
}

现在,正如您可能预期的那样,这会在 if let masterCommands = mastervc.commands { ,因为 UIViewController doesn't contain the commands variable out of the box. My question is: how can I have ui视图控制器 have that variable? Just like all controllers can override keycommands`默认情况下?