[英]Caliburn.Micro nested ViewModels best practice
这是一个很长的问题,所以请耐心等待。
目前我正在开发一个小工具,旨在帮助我跟踪我的故事中无数的角色。
该工具执行以下操作:
Conductor<Screen>.Collection.OneActive
,它将打开一个新的CharacterViewModel
,它派生自Screen
。 Character
获取将通过IEventAggregator
消息系统打开的IEventAggregator
。 CharacterViewModel
还具有各种属性,这些属性是子ViewModel,它们绑定到各种子视图。 这里是我的问题:目前我手动初始化子的ViewModels当ChracterViewModel
被初始化。 但这对我来说听起来很可疑,我很确定有更好的方法可以做到这一点,但我看不出应该怎么做。
这是CharacterViewModel
的代码:
/// <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;
}
}
对于完成清酒我也给你一个子ViewModels。 其他一个并不重要,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);
}
}
}
我已经阅读过Screens,Conductors and Composition , IResult和Coroutines , 并浏览了其余的文档,但不知怎的,我找不到我要找的东西。
//编辑:我应该提一下我工作的代码就好了。 我只是对它不满意,因为我认为我不太了解MVVM的概念,因此制作错误的代码。
让一个ViewModel实例化几个子ViewModel没有任何问题。 如果您正在构建更大或更复杂的应用程序,那么如果您希望保持代码的可读性和可维护性,这几乎是不可避免的。
在您的示例中,每当您创建CharacterViewModel
实例时,都要实例化所有四个子ViewModel。 每个子ViewModels都将IEventAggregator
作为依赖项。 我建议您将这四个子ViewModel视为主要CharacterViewModel
依赖项,并通过构造函数导入它们:
[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属性的setter设置为private。
更改您的子ViewModels以通过构造函数注入导入IEventAggregator
:
[ImportingConstructor]
public CharacterGeneralViewModel(IEventAggregator eventAggregator)
{
this.eventAggregator = eventAggregator;
}
在您的示例中,其中两个子ViewModel在其构造函数中传递了Character
数据的实例,这意味着依赖关系。 在这些情况下,我会给每个子ViewModel一个公共的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();
}
对于只通过EventAggregator
更新Character
数据的子ViewModel,请在构造函数中保留this.eventAggregator.Subscribe(this)
调用。
如果页面无法实际运行任何子ViewModel,则可以通过属性导入初始化这些VM属性:
[Import]
public CharacterGeneralViewModel CharacterGeneralViewModel { get; set; }
在构造函数完成运行之后才会发生属性导入。
我还建议通过构造函数注入来处理ICharacterSaveService
的实例化,而不是每次保存数据时显式创建新实例。
MVVM的主要目的是允许前端设计人员在可视化工具(Expression Blend)和编码器中处理UI的布局,以实现行为和业务而不会相互干扰。 ViewModel公开要绑定到视图的数据,描述视图在抽象级别的行为,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,并且有些情况下它不是最好的解决方案。 有时最好的解决方案是使用ViewModel抛出额外的抽象层,然后编写一些代码隐藏。 因此,尽管它对于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适合MVVM模式的陷阱。 如果你有一些图形复杂的用户控件,它只是更好地有一些代码隐藏,那么这就是你应该做的。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.