[英]Caliburn.Micro nested ViewModels best practice
這是一個很長的問題,所以請耐心等待。
目前我正在開發一個小工具,旨在幫助我跟蹤我的故事中無數的角色。
該工具執行以下操作:
Conductor<Screen>.Collection.OneActive
,它將打開一個新的CharacterViewModel
,它派生自Screen
。 Character
獲取將通過IEventAggregator
消息系統打開的IEventAggregator
。 CharacterViewModel
還具有各種屬性,這些屬性是子ViewModel,它們綁定到各種子視圖。 這里是我的問題:目前我手動初始化子的ViewModels當ChracterViewModel
被初始化。 但這對我來說聽起來很可疑,我很確定有更好的方法可以做到這一點,但我看不出應該怎么做。
這是CharacterViewModel
的代碼:
/// <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;
}
}
對於完成清酒我也給你一個子ViewModels。 其他一個並不重要,因為它們的結構相同,只是執行不同的任務。
/// <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);
}
}
}
我已經閱讀過Screens,Conductors and Composition , IResult和Coroutines , 並瀏覽了其余的文檔,但不知怎的,我找不到我要找的東西。
//編輯:我應該提一下我工作的代碼就好了。 我只是對它不滿意,因為我認為我不太了解MVVM的概念,因此制作錯誤的代碼。
讓一個ViewModel實例化幾個子ViewModel沒有任何問題。 如果您正在構建更大或更復雜的應用程序,那么如果您希望保持代碼的可讀性和可維護性,這幾乎是不可避免的。
在您的示例中,每當您創建CharacterViewModel
實例時,都要實例化所有四個子ViewModel。 每個子ViewModels都將IEventAggregator
作為依賴項。 我建議您將這四個子ViewModel視為主要CharacterViewModel
依賴項,並通過構造函數導入它們:
[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,您可以將子ViewModel屬性的setter設置為private。
更改您的子ViewModels以通過構造函數注入導入IEventAggregator
:
[ImportingConstructor]
public CharacterGeneralViewModel(IEventAggregator eventAggregator)
{
this.eventAggregator = eventAggregator;
}
在您的示例中,其中兩個子ViewModel在其構造函數中傳遞了Character
數據的實例,這意味着依賴關系。 在這些情況下,我會給每個子ViewModel一個公共的Initialize()
方法,您可以在其中設置Character
數據並在那里激活事件聚合器訂閱:
public Initialize(Character character)
{
this.Character = character;
this.eventAggregator.Subscribe(this);
}
然后在CharacterViewModel
OnInitialize()
方法中調用此方法:
protected override void OnInitialize()
{
this.CharacterMetadataViewModel.Initialize(this.Character);
this.CharacterCharacteristicsViewModel.Initialize(this.Character);
this.eventAggregator.PublishOnUIThread(new CharacterMessage
{
Data = this.Character
});
base.OnInitialize();
}
對於只通過EventAggregator
更新Character
數據的子ViewModel,請在構造函數中保留this.eventAggregator.Subscribe(this)
調用。
如果頁面無法實際運行任何子ViewModel,則可以通過屬性導入初始化這些VM屬性:
[Import]
public CharacterGeneralViewModel CharacterGeneralViewModel { get; set; }
在構造函數完成運行之后才會發生屬性導入。
我還建議通過構造函數注入來處理ICharacterSaveService
的實例化,而不是每次保存數據時顯式創建新實例。
MVVM的主要目的是允許前端設計人員在可視化工具(Expression Blend)和編碼器中處理UI的布局,以實現行為和業務而不會相互干擾。 ViewModel公開要綁定到視圖的數據,描述視圖在抽象級別的行為,並經常充當后端服務的中介。
沒有一種“正確”的方法可以做到這一點,並且有些情況下它不是最好的解決方案。 有時最好的解決方案是使用ViewModel拋出額外的抽象層,然后編寫一些代碼隱藏。 因此,盡管它對於整個應用程序來說是一個很好的結構,但不要陷入強迫所有內容適合MVVM模式的陷阱。 如果你有一些圖形復雜的用戶控件,它只是更好地有一些代碼隱藏,那么這就是你應該做的。
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