将变量添加到所有 UIViewControllers

Posted 2023-02-24

【中文标题】将变量添加到所有 UIViewControllers

【英文标题】：add variable to all UIViewControllers

【发布时间】：2018-07-12 09:26:42

【问题描述】：

我是 Swift 新手，我正在尝试在练习应用中实现自定义 UIKeyCommand 架构。我为基础UISplitViewController 编写了下面的扩展，以在屏幕上的当前视图中显示所有UIKeyCommands。

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，正如您所料，这会在 if let masterCommands = mastervc.commands 处引发错误，因为默认情况下是 UIViewController doesn't contain the commands variable out of the box. My question is: how can I haveUIViewControllerhave that variable? Just like all controllers can overridekeyCommands`？

【参考方案1】：

您必须创建一个带有命令变量的协议，并使您的视图控制器符合它（第 1 步）。您可以为特定视图控制器提供值，也可以提供默认实现。

第 1 步：- 使用您需要的变量创建协议。

protocol Commandable
   var commands: [String]set get

extension Commandable
   var commands: [String]
        getreturn ["hello","world"]
        set
    

第 2 步：- 然后使您使用的控制器符合它

第 3 步：- 更改上述代码以获取命令

if let commandProtocol = masterVC as? Commandable

    let commands = commandProtocol.commands

else
    // handle it

确保变量是唯一的，以免意外覆盖它。

谢谢。

【参考方案2】：

您可以创建UIViewController 的扩展名并将该属性添加到UIViewController 的扩展名上。然后，您将在 UISplitViewController 或任何其他自定义 ViewControllers 等子视图控制器上获得它。想了解更多关于扩展的信息，Which can be added on extension or what can be done by extension??