在我的开发学习中,我觉得我必须学习更多关于接口的知识。
我经常读到它们,但我似乎无法理解它们。
我读过这样的例子:动物基类,IAnimal接口的东西,如“Walk”,“Run”,“GetLegs”等-但我从来没有工作过,觉得“嘿,我应该在这里使用接口!”
我错过了什么?为什么这个概念对我来说这么难理解!我只是害怕这样一个事实,我可能从来没有意识到一个具体的需要-主要是由于一些缺失的理解他们!这让我觉得我作为一名开发人员缺少了一些东西!如果有人有过这样的经历,并取得了突破,我会很感激一些关于如何理解这个概念的建议。谢谢你!
I like Jimmy's answer a lot, but I feel I need to add something to it. The key to the whole thing is the "able" in IProcessable . It indicates a capability (or property, but meaning "intrinsic quality", not in the sense of C# properties) of the object that implements the interface. IAnimal is probably not a good example for an interface, but IWalkable might be a good interface to have if your system has many things that can walk. You might have classes derived from Animal such as Dog, Cow, Fish, Snake. The first two would probably implement IWalkable, the latter two don't walk, so they wouldn't. Now you ask "why not just have another superclass, WalkingAnimal, that Dog and Cow derive from?". The answer is when you have something completely outside the inheritance tree that also can walk, such as a robot. Robot would implement IWalkable, but probably wouldn't derive from Animal. If you want a list of things that can walk, you type it as IWalkable and you can put all walking animals plus robots in the list.
现在,将IWalkable替换为IPersistable这样更像软件的东西,这样的类比就更接近你在实际程序中看到的情况了。
I like Jimmy's answer a lot, but I feel I need to add something to it. The key to the whole thing is the "able" in IProcessable . It indicates a capability (or property, but meaning "intrinsic quality", not in the sense of C# properties) of the object that implements the interface. IAnimal is probably not a good example for an interface, but IWalkable might be a good interface to have if your system has many things that can walk. You might have classes derived from Animal such as Dog, Cow, Fish, Snake. The first two would probably implement IWalkable, the latter two don't walk, so they wouldn't. Now you ask "why not just have another superclass, WalkingAnimal, that Dog and Cow derive from?". The answer is when you have something completely outside the inheritance tree that also can walk, such as a robot. Robot would implement IWalkable, but probably wouldn't derive from Animal. If you want a list of things that can walk, you type it as IWalkable and you can put all walking animals plus robots in the list.
现在,将IWalkable替换为IPersistable这样更像软件的东西,这样的类比就更接近你在实际程序中看到的情况了。
使用接口有很多目的。
Use in polymorphic behavior. Where you want to call specific methods of a child class with an inteface having a reference to the child class.
Having a contract with classes to implement all of the methods where it is necessary, like most common use is with COM objects , where a wrapper class is generated on a DLL which inherits the interface; these methods are called behind the scenes, and you just need to implement them but with the same structure as defined in the COM DLL which you can only know through the interface that they expose.
To reduce memory usage by loading specific methods in a class. Like if you have three business objects and they are implemented in a single class, you can use three interfaces.
例如IUser, IOrder, IOrderItem
public interface IUser()
{
void AddUser(string name ,string fname);
}
// Same for IOrder and IOrderItem
//
public class BusinessLayer: IUser, IOrder, IOrderItem
{
public void AddUser(string name ,string fname)
{
// Do stuffs here.
}
// All methods from all interfaces must be implemented.
}
如果你只想添加一个用户,可以这样做:
IUser user = new (IUser)BusinessLayer();
// It will load all methods into memory which are declared in the IUser interface.
user.AddUser();
我偶尔也会使用接口,下面是我最新的用法(名称已经概括了):
我在WinForm上有一堆需要将数据保存到业务对象的自定义控件。一种方法是分别调用每个控件:
myBusinessObject.Save(controlA.Data);
myBusinessObject.Save(controlB.Data);
myBusinessObject.Save(controlC.Data);
这个实现的问题是,每当我添加一个控件,我必须进入我的“保存数据”方法,并添加新的控件。
我改变了我的控件来实现一个ISaveable接口,它有一个方法SaveToBusinessObject(…),所以现在我的“保存数据”方法只是通过控件迭代,如果它发现一个是ISaveable,它调用SaveToBusinessObject。所以现在当需要一个新的控件时,所有人要做的就是在该对象中实现ISaveable(并且永远不要触及其他类)。
foreach(Control c in Controls)
{
ISaveable s = c as ISaveable;
if( s != null )
s.SaveToBusinessObject(myBusinessObject);
}
接口通常未被意识到的好处是本地化修改。定义之后,您很少会更改应用程序的整体流程,但通常会在细节级别上进行更改。当您将细节保存在特定对象中时,ProcessA中的更改将不会影响ProcessB中的更改。(基类也有这个好处。)
编辑:另一个好处是行动的专一性。就像在我的例子中,我所要做的就是保存数据;我不关心它是什么类型的控件,或者它是否可以做任何其他事情——我只想知道我是否可以保存控件中的数据。它使我的保存代码非常清晰——没有检查它是否为文本、数字、布尔值或任何东西,因为自定义控件处理所有这些。
它解决了一个具体的问题:
你有a b c d四种不同类型。在你的代码中,你可以这样写:
a.Process();
b.Process();
c.Process();
d.Process();
为什么不让他们实现IProcessable呢
List<IProcessable> list;
foreach(IProcessable p in list)
p.Process();
当你添加50种类型的类,它们都做同样的事情时,这种伸缩性会更好。
另一个具体问题是:
你有没有看过System.Linq.Enumerable?它定义了大量的扩展方法,可以对实现IEnumerable的任何类型进行操作。因为任何实现IEnumerable的东西基本上都在说“我支持无序foreach类型模式中的迭代”,所以你可以为任何可枚举类型定义复杂的行为(Count、Max、Where、Select等)。