汇总成员的介绍 [英] Presentation of an Aggregate Member

问题描述

如何出于展示的目的公开聚合成员，同时防止该成员直接被修改?因此，为了在UI上显示该成员，我需要对该成员进行只读访问，例如:

How do you expose an aggregate member for the purpose of presentation, while at the same time preventing that member from getting modified directly? So, I need something like read-only access to that member for the purpose of showing it on UI, For example:

class A {

    B b;

    void doSomething() {
        b.update();
    }

}

class B {

    String getTitle() {
        return title;
    }

    Items getItems() {
        return items;
    }

    void update() {
        ...
    }

}

interface SomeView {

    void show(Items items);

}

一种快捷方法是添加方法A::getB()并调用someView.show(b.getItems())，但是随后返回的B实例可以在A之外进行修改(B::update()可以在A).

The quick-and-dirty solution would be to add a method A::getB() and call someView.show(b.getItems()) but then the returned B instance could be modified outside of A (the B::update() could be called outside A).

我正在考虑几种解决方案，但是不确定哪种方案最好，或者是否已经有一种普遍的做法.

I am thinking of several solutions but not quite sure which are best or if there is already a common practice to do so.

我想到的解决方案之一是拥有B的只读版本，该版本由A返回.

One of the solution that I have in mind is having a read-only version of B that is returned by A.

class A {

    ReadOnlyB getReadOnlyB() {
        return new ReadOnlyB(b);
    }

}

class ReadOnlyB {

    B b;

    ReadOnlyB(B b) {
        this.b = b;
    }

    String getTitle() {
        return b.getTitle();
    }

    Items getItems() {
        return b.getItems();
    }

}

推荐答案

您可以对B使用只读接口.在内部，在A类中，您使用类B，但是在外部(对于客户端)，您提供了B只读接口.这是一个示例:

You could use read-only interfaces for B. Internally, in A class, you use the class B but to the outside (to the clients) you give a read-only interface of B. Here is a sample:

class A 
{
    private B b;

    void doSomething() {
        //internally you use this.b
        b.update();
    }

    //please name this method according to its purpose
    ReadOnlyB getB()
    {
       return b;
    }
}

class B implements ReadOnlyB
{
    String getTitle() {
        return title;
    }

    Items getItems() {
        return items;
    }

    void update() {
        ...
    }

}

//please name this interface according to its purpose!
interface ReadOnlyB
{
    Items getItems();
}

interface SomeView 
{
    void show(Items items);
}

但是，这会破坏迪米特法律.最好从A返回Items，如下所示:

However, this would break the Law of Demeter. It would be better to return the Items from A, like this:

class A 
{
    private B b;

    void doSomething() {
        b.update();
    }

    Items getItems()
    {
       return b.getItems();
    }
}

这篇关于汇总成员的介绍的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！