Caliburn.Micro嵌套ViewModels最佳实践

鲁尔波特爱国者

这是一个很长的问题,请耐心等待。

目前,我正在开发一个小工具,旨在帮助我跟踪“故事”中的众多角色。

该工具执行以下操作:

  • 将当前存储为json的字符加载到磁盘上,并将它们存储在列表中,该列表通过列表框在Shell中显示。
  • 如果用户随后打开一个字符,则Shell(即a Conductor<Screen>.Collection.OneActive)将打开一个新的字符(CharacterViewModel源自)Screen
  • Character获取即将通过要打开的汉字IEventAggregator信息系统。
  • CharacterViewModel还具有其是子的ViewModels结合到各种子视图的各种属性。

这是我的问题:当前,我在初始化时手动初始化子ViewModels ChracterViewModel但这对我来说听起来像是可疑的,我很确定有更好的方法可以做到这一点,但是我不知道应该怎么做。

这是的代码CharacterViewModel

/// <summary>ViewModel for the character view.</summary>
public class CharacterViewModel : Screen, IHandle<DataMessage<ICharacterTagsService>>
{
    // --------------------------------------------------------------------------------------------------------------------
    // Fields
    // -------------------------------------------------------------------------------------------------------------------

    /// <summary>The event aggregator.</summary>
    private readonly IEventAggregator eventAggregator;

    /// <summary>The character tags service.</summary>
    private ICharacterTagsService characterTagsService;

    // --------------------------------------------------------------------------------------------------------------------
    // Constructors & Destructors
    // -------------------------------------------------------------------------------------------------------------------

    /// <summary>Initializes a new instance of the <see cref="CharacterViewModel"/> class.</summary>
    public CharacterViewModel()
    {
        if (Execute.InDesignMode)
        {
            this.CharacterGeneralViewModel = new CharacterGeneralViewModel();

            this.CharacterMetadataViewModel = new CharacterMetadataViewModel();
        }
    }

    /// <summary>Initializes a new instance of the <see cref="CharacterViewModel"/> class.</summary>
    /// <param name="eventAggregator">The event aggregator.</param>
    [ImportingConstructor]
    public CharacterViewModel(IEventAggregator eventAggregator)
        : this()
    {
        this.eventAggregator = eventAggregator;
        this.eventAggregator.Subscribe(this);
    }

    // --------------------------------------------------------------------------------------------------------------------
    // Properties
    // -------------------------------------------------------------------------------------------------------------------

    /// <summary>Gets or sets the character.</summary>
    public Character Character { get; set; }

    /// <summary>Gets or sets the character general view model.</summary>
    public CharacterGeneralViewModel CharacterGeneralViewModel { get; set; }

    /// <summary>Gets or sets the character metadata view model.</summary>
    public CharacterMetadataViewModel CharacterMetadataViewModel { get; set; }

    /// <summary>Gets or sets the character characteristics view model.</summary>
    public CharacterApperanceViewModel CharacterCharacteristicsViewModel { get; set; }

    /// <summary>Gets or sets the character family view model.</summary>
    public CharacterFamilyViewModel CharacterFamilyViewModel { get; set; }

    // --------------------------------------------------------------------------------------------------------------------
    // Methods
    // -------------------------------------------------------------------------------------------------------------------

    /// <summary>Saves a character to the file system as a json file.</summary>
    public void SaveCharacter()
    {
        ICharacterSaveService saveService = new JsonCharacterSaveService(Constants.CharacterSavePathMyDocuments);

        saveService.SaveCharacter(this.Character);

        this.characterTagsService.AddTags(this.Character.Metadata.Tags);
        this.characterTagsService.SaveTags();
    }

    /// <summary>Called when initializing.</summary>
    protected override void OnInitialize()
    {
        this.CharacterGeneralViewModel = new CharacterGeneralViewModel(this.eventAggregator);
        this.CharacterMetadataViewModel = new CharacterMetadataViewModel(this.eventAggregator, this.Character);
        this.CharacterCharacteristicsViewModel = new CharacterApperanceViewModel(this.eventAggregator, this.Character);
        this.CharacterFamilyViewModel = new CharacterFamilyViewModel(this.eventAggregator);

        this.eventAggregator.PublishOnUIThread(new CharacterMessage
        {
            Data = this.Character
        });


        base.OnInitialize();
    }

    /// <summary>
    /// Handles the message.
    /// </summary>
    /// <param name="message">The message.</param>
    public void Handle(DataMessage<ICharacterTagsService> message)
    {
        this.characterTagsService = message.Data;
    }
}

对于清酒,我还为您提供了一个子ViewModels。其他的一个并不重要,因为它们的结构相同,只是执行不同的任务。

/// <summary>The character metadata view model.</summary>
public class CharacterMetadataViewModel : Screen
{
    /// <summary>The event aggregator.</summary>
    private readonly IEventAggregator eventAggregator;

    /// <summary>Initializes a new instance of the <see cref="CharacterMetadataViewModel"/> class.</summary>
    public CharacterMetadataViewModel()
    {
        if (Execute.InDesignMode)
        {
            this.Character = DesignData.LoadSampleCharacter();
        }
    }

    /// <summary>Initializes a new instance of the <see cref="CharacterMetadataViewModel"/> class.</summary>
    /// <param name="eventAggregator">The event aggregator.</param>
    /// <param name="character">The character.</param>
    public CharacterMetadataViewModel(IEventAggregator eventAggregator, Character character)
    {
        this.Character = character;

        this.eventAggregator = eventAggregator;
        this.eventAggregator.Subscribe(this);
    }

    /// <summary>Gets or sets the character.</summary>
    public Character Character { get; set; }

    /// <summary>
    /// Gets or sets the characters tags.
    /// </summary>
    public string Tags
    {
        get
        {
            return string.Join("; ", this.Character.Metadata.Tags);
        }

        set
        {
            char[] delimiters = { ',', ';', ' ' };

            List<string> tags = value.Split(delimiters, StringSplitOptions.RemoveEmptyEntries).ToList();

            this.Character.Metadata.Tags = tags;
            this.NotifyOfPropertyChange(() => this.Tags);
        }
    }
}

我已经读过《屏幕,导体和成分》,《IResult》和《协程》并浏览了其余的文档,但是不知何故找不到所需的内容。

// edit:我应该提到我的代码可以正常工作。我只是对它不满意,因为我认为我不太了解MVVM的概念,因此编写了错误的代码。

Teagans爸爸

一个ViewModel实例化多个子ViewModel并没有错。如果要构建更大或更复杂的应用程序,则要保持代码的可读性和可维护性,这是不可避免的。

在您的示例中,每当创建的实例时,您都将实例化所有四个子ViewModel CharacterViewModel每个子ViewModels都IEventAggregator作为依赖项。我建议您将这四个子ViewModel作为主要对象的依赖项,CharacterViewModel并通过构造函数将其导入:

[ImportingConstructor]
public CharacterViewModel(IEventAggregator eventAggregator,
                            CharacterGeneralViewModel generalViewModel,
                            CharacterMetadataViewModel metadataViewModel,
                            CharacterAppearanceViewModel appearanceViewModel,
                            CharacterFamilyViewModel familyViewModel)
{
    this.eventAggregator = eventAggregator;
    this.CharacterGeneralViewModel generalViewModel;
    this.CharacterMetadataViewModel = metadataViewModel;
    this.CharacterCharacteristicsViewModel = apperanceViewModel;
    this.CharacterFamilyViewModel = familyViewModel;

    this.eventAggregator.Subscribe(this);
}

因此,您可以将子ViewModel属性上的设置器设为私有。

更改您的子ViewModels以IEventAggregator通过构造函数注入导入

[ImportingConstructor]
public CharacterGeneralViewModel(IEventAggregator eventAggregator)
{
    this.eventAggregator = eventAggregator;
}

在您的示例中,这些子ViewModel中的两个Character在其构造函数中传递了一个数据实例,这意味着一个依赖关系。在这些情况下,我将为每个子ViewModel提供一个公共Initialize()方法,您可以在其中设置Character数据并在那里激活事件聚合器订阅:

public Initialize(Character character)
{
    this.Character = character;
    this.eventAggregator.Subscribe(this);   
}

然后在您的CharacterViewModel OnInitialize()方法中调用此方法:

protected override void OnInitialize()
{    
    this.CharacterMetadataViewModel.Initialize(this.Character);
    this.CharacterCharacteristicsViewModel.Initialize(this.Character);    

    this.eventAggregator.PublishOnUIThread(new CharacterMessage
    {
        Data = this.Character
    });


    base.OnInitialize();
}

对于仅Character通过来更新数据的子ViewModels EventAggregator,将this.eventAggregator.Subscribe(this)调用保留在构造函数中。

如果页面正常运行实际上不需要您的任何子ViewModel,则可以通过属性导入来初始化这些VM属性:

[Import]
public CharacterGeneralViewModel CharacterGeneralViewModel { get; set; }

在构造函数完成运行之前,不会进行属性导入。

我还建议您也处理ICharacterSaveService通过构造函数注入的实例化,而不是每次保存数据时都显式创建一个新实例。

MVVM的主要目的是允许前端设计人员使用可视化工具(Expression Blend)来处理UI的布局,并允许编码人员在不相互干扰的情况下实现行为和业务。ViewModel公开要绑定到视图的数据,以抽象级别描述视图的行为,并经常充当后端服务的中介。

没有一种“正确”的方法可以做到这一点,并且在某些情况下它不是最佳解决方案。有时,最好的解决方案是扔掉使用ViewModel的额外抽象层,然后编写一些代码隐藏。因此,尽管它对于您的整个应用程序来说是一个很好的结构,但不要陷入强迫所有内容都适合MVVM模式的陷阱。如果您在图形上有一些复杂的用户控件,那么在其中隐藏一些代码会更好,那么这就是您应该做的。

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