一种从多个类继承的方法 [英] A way to inherit from multiple classes

问题描述

我想在我的新课程中使用两个课程。第一个实现滑动删除，第二个实现长按手势：

I have two classes I want to use in my new class. The first one implements a swipe to delete and the second enables a long press gesture:

class DeleteItem: UITableViewCell {
}

class OpenDetail: UITableViewCell {
}

自Swift不允许类继承多个类，以下示例显然不起作用：

Since Swift doesn't allow a class to inherit from multiple classes the following example obviously won't work:

class ItemViewCell: DeleteItem, OpenDetail {
}

所以为了创建 ItemViewCell 并且有两个选项，我必须让其中一个类继承彼此：

So in order to create ItemViewCell and having both options, I'll have to have one of the classes to inherit from each other:

class DeleteItem: UITableViewCell {
}

class OpenDetail: DeleteItem {
}

class ItemViewCell: OpenDetail {
}

问题是，如果我只想要长按手势，我将不得不创建一个新类而不继承 DeleteItem 。有没有更好的方法呢？

The problem is, if I only want the long press gesture I'll have to create a new class without inheriting from DeleteItem. Is there a better way of doing this?

推荐答案

这是使用协议和协议扩展的完美案例。 swift 协议就像Java中的接口一样。协议可以定义一组功能，这些功能必须由想要符合该协议的实体来实现，而且协议也可以定义必须存在于这些实体中的属性。例如：

This is the perfect case for using Protocols and Protocol extension. A swift protocol is like an interface in Java for example. A protocol can define a set of functions which has to be implemented by the entities which want to conform to this protocol, moreover a protocol can define properties which has to be present in these entities too. For example:

protocol ItemDeleter {
  var deletedCount: Int {get set}
  func deleteItem(item: ItemType)
}

问题是，每个实体都必须提供自己的实现 func deleteItem（item：ItemType）即使多个实体共享相同的删除项目逻辑，协议扩展也会派上用场。例如：

The problem is, that each entity would have to provide its own implementation of func deleteItem(item: ItemType) even if multiple entities share the same logic of deleting an item, this where a protocol extension comes in handy. For example:

extension ItemDeleter {
  func deleteItem(item: ItemType) {
    // logic needed to delete an item

    // maybe incremented deletedCount too
    deletedCount++
  }
}

然后你可以让你的 ItemViewCell 符合 ItemDeleter 协议，在这种情况下，您只需要确保 ItemViewCell 具有属性 deletedCount：Int 。它不需要为 func deleteItem（item：ItemType）提供实现，因为协议本身提供了此函数的默认实现，但是您可以在类中覆盖它，并将使用新的实施。这同样适用于 DetailOpener协议。

Then you could make your ItemViewCell conform to the ItemDeleter protocol, in this case all you need is to make sure that ItemViewCell has a property deletedCount: Int. It does not need to provide an implementation for func deleteItem(item: ItemType) as the protocol itself provides a default implementation for this function, however you can override it in your class, and the new implementation will be used. The same applies for DetailOpener protocol.

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