如何用IOC替换switch语句,以便我可以保持SOLID原则

Question

我想避免使用switch语句.我有30多种文档类型.还有可能我需要添加更多的文档类型.我宁愿传递IDocument并且具有在IDocument的实现中指定的类型.我忘了提到的其他东西是ProgressNoteViewModel,LabViewModel ...都继承自WorkspaceViewModel,所有具体实现构造函数都将类型IPatient作为参数.我也使用Castle作为我的IoC容器

我想将代码重构为类似的东西

viewModel = new TreeViewModel(repository.GetPatientDocumentListing(IDocumentType);
this.DocTreeViewModel = viewModel;
//How would I then be able to instantiate the right ViewModel
//based on IDocumentType and also pass a object into the
//constructor that is not know at compile time

我有以下代码:

switch (docType)
{
    case "ProgressNotes":
        viewModel = new TreeViewModel(repository.GetPatientProgressNotes());
        this.DocTreeViewModel = viewModel;
        ProgressNoteViewModel workspace = ProgressNoteViewModel.NewProgressNoteViewModel(_patient);
        break;
    case "Labs":
        viewModel = new TreeViewModel(repository.GetPatientLabs());
        this.DocTreeViewModel = viewModel;
        LabViewModel workspace = LabViewModel.NewLabViewModel(_patient);
        break;
}
this.Workspaces.Add(workspace);
this.SetActiveWorkspace(workspace);

Answer 1

完全未经测试：

public class ViewModelBuilderFactory
{
    public IViewModelBuilder GetViewModelBuilder (string docType, IRepository repository)
    {
        switch (docType)
        {
            case "ProgressNotes":
                return new ProgressNotesViewModelBuilder(repository);
            case "Labs":
                return new LabsViewModelBuilder(repository);
            default:
                throw new ArgumentException(
                    string.Format("docType \"{0}\" Invalid", docType);
        }
    }
}

public interface IViewModelBuilder
{
    TreeViewModel GetDocTreeViewModel();
    WorkSpace GetWorkSpace(Patient patient);
}

public class LabsViewModelBuilder : IViewModelBuilder
{
    private IRepository _repository;
    public LabsViewModelBuilder(IRepository repository)
    {
        _repository = repository;
    }

    public TreeViewModel GetDocTreeViewModel()
    {
        return new TreeViewModel(_repository.GetPatientLabs());
    }

    public Workspace GetWorkspace(Patient patient)
    {
        return LabViewModel.NewLabViewModel(patient);
    }
}

public class ProgressNotesViewModelBuilder : IViewModelBuilder
{
    private IRepository _repository;
    public ProgressNotesViewModelBuilder(IRepository repository)
    {
        _repository = repository;
    }

    public TreeViewModel GetDocTreeViewModel()
    {
        return new TreeViewModel(_repository.GetPatientProgressNotes());
    }

    public Workspace GetWorkspace(Patient patient)
    {
        return ProgressNoteViewModel.NewProgressNoteViewModel(patient);
    }
}

现在你的调用代码是：

ViewModelBuilderFactory factory = new ViewModelBuilderFactory();
IViewModelBuilder modelBuilder = factory.GetViewModelBuilder(docType, repository);
this.DocTreeViewModel = modelBuilder.GetDocTreeViewModel();
Workspace workspace = modelBuilder.GetWorkspace(patient);
this.Workspaces.Add(workspace);
this.SetActiveWorkspace(workspace);

[自第一篇文章以来已进行 4 次编辑；不断看到错误]

[进一步编辑注意到您正在使用 Castle IOC]

在你的 Castle xml 配置中，你可以添加（我在这里只是对 Castle 有了模糊的了解）

<component id="ProgressNotesViewModelBuilder"
           type="MyNamespace.ProgressNotesViewModelBuilder, MyAssembly">
    <parameters>
        <!-- reference to repository here -->
    </parameters>
</component>
<component id="LabsViewModelBuilder"
           type="MyNamespace.LabsViewModelBuilder, MyAssembly">
    <parameters>
        <!-- reference to repository here -->
    </parameters>
</component>

那么你不需要ViewModelBuilderFactory，你可以直接替换

IViewModelBuilder modelBuilder = factory.GetViewModelBuilder(docType, repository);

和

IViewModelBuilder modelBuilder = (IViewModelBuilder)
    container.Resolve(docType + "ViewModelBuilder");

现在您根本不需要 switch 语句。

然而，值得注意的是，开关并不是邪恶的，它们只是闻起来很难闻，所有难闻的气味都应该与所有闻起来香的东西隔离开来；这就是工厂模式想要实现的目标。