接口实现中多个if语句的最佳设计模式

Question

我的IComposerc#项目中有一个界面:

public interface IComposer
{
    string GenerateSnippet(CodeTree tree);
}

CodeTree是一个基类,包含一个List<CodeTree>继承自的类CodeTree.例如:

public class VariablesDecleration : CodeTree
{
     //Impl
}

public class LoopsDecleration : CodeTree
{
     //Impl
}

我可以有几个实现的类,IComposer每个我都有GenerateSnippet循环List<CodeTree>,基本上做:

foreach (CodeTree code in tree.Codes)
{
    if (code.GetType() == typeof(VariablesDecleration))
    {
        VariablesDecleration codeVariablesDecleration = (VariablesDecleration) code;
        // do class related stuff that has to do with VariablesDecleration
    }
    else if (code.GetType() == typeof(LoopsDecleration))
    {
        LoopsDecleration codeLoopsDecleration = (LoopsDecleration) code;
        // do class related stuff that has to do with LoopsDecleration
    }
}

我在每个实现的类中重复这些foreach和if语句IComposer.

我想知道是否有更好的设计模式来处理这种情况.让我说tommrow我添加了一个继承自的新类CodeTree- 我将不得不遍历所有实现IComposer和修改它们的类.

我在考虑访问者设计模式 - 但不确定并且不确定是否以及如何实现它.访客是否为这种情况提供了正确的解决方案？

Answer 1

移动与内部特定类相关的实现,VariablesDecleration并LoopsDecleration提供一个抽象实现CodeTree.然后在你的循环中,简单地在CodeTree中调用该方法,而不用if ... else检查.

public class VariablesDecleration : CodeTree
{
    //Impl
    public void SomeStuff()
    {
        //... specific to Variables
    }
}

public class LoopsDecleration : CodeTree
{
    //Impl
    public void SomeStuff()
    {
        //... specific to Loops
    }
}

public class CodeTree : ICodeTree
{
    void SomeStuff();
}

foreach (CodeTree code in tree.Codes)
{
    code.SomeStuff();
}

根据评论,你可能需要这样的东西:

public interface IComposer
{
    string DoStuff();
}

public class LoopComposer1 : IComposer
{
    string DoStuff(){ .. }
}

public class VariableComposer1 : IComposer
{
    string DoStuff(){ .. }
}

public class ComposerCollection
{
    private IEnumerable<IComposer> composers;
    string GenerateSnippet()
    {
        foreach(var composer in composers)
        {
            composer.DoStuff();
        }
        ...
        ...
    }
}

当然,现在关系已经颠倒了,你的代码树或它的创建者必须为它定义作曲家集合.