WPF应用：理解与实现Model-View-ViewModel设计模式

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本文档深入探讨了在Windows Presentation Foundation (WPF)应用程序开发中采用Model-View-ViewModel (MVVM)设计模式的最佳实践。发表于2009年，作者Josh Smith在《Microsoft Developer Magazine》上分享了他的见解，指出MVVM相对于传统的Model-View-Presenter (MVP)模式在WPF中具有更高的优势。 MVVM设计模式的核心在于将应用程序的逻辑、视图和数据模型分离，使得代码结构清晰且易于维护。以下是一些关键知识点： 1. **MVVM模式与WPF的关系**： MVVM模式特别适合WPF，因为它强调组件之间的松耦合和数据驱动。WPF天生支持数据绑定，MVVM则提供了组织代码的方式，使开发者能够专注于业务逻辑，而不是UI细节。 2. **MVVM的优势**： - **可测试性**：由于模型、视图和命令的分离，每个部分都可以独立进行单元测试。 - **可维护性**：简化了代码结构，提高了团队协作效率。 - **可重用性**：视图模型可以跨多个视图复用，降低了代码冗余。 - **逻辑集中**：业务逻辑集中在视图模型中，避免了直接操作视图。 3. **构建一个MVVM应用**： - **步骤**：从创建ViewModel基类开始，逐步定义Command ViewModel类和主窗口ViewModel类，然后将视图绑定到ViewModel。 - **实例化**：例如，NewCustomerDataEntryForm和AllCustomersView分别对应单独的ViewModel，用于数据输入和展示所有客户信息。 4. **数据模型和存储**： - **分离数据访问层**：通过数据模型和数据仓库（Repository）实现数据管理，确保对数据库或API的访问逻辑不直接与视图模型关联。 5. **用户界面设计**： - **秩序与混乱**：尽管开发过程中可能会遇到交互设计和视觉设计的复杂性，但MVVM通过将逻辑抽象出来，有助于保持UI的清晰和一致性。 6. **命令的处理**： - **RelayingCommand**：这是一种策略，用于在ViewModel中封装复杂的命令逻辑，以便在视图上触发时执行，从而进一步降低视图和业务逻辑的耦合。总结，这篇指南提供了一个实际的框架来指导开发者如何在WPF项目中采用MVVM设计模式，帮助他们构建高效、可维护和模块化的应用程序。通过遵循这些原则，开发者可以创建出既美观又功能强大的用户界面，同时保持代码的清晰度和可扩展性。

2015/10/13 PatternsWPFAppsWithTheModelViewViewModelDesignPattern

https://msdn.microsoft.com/enus/magazine/dd419663.aspx 3/11

Two other features of WPF that make this pattern so usable are data templates and the resource

system. Data templates apply Views to ViewModel objects shown in the user interface. You can

declare templates in XAML and let the resource system automatically locate and apply those

templates for you at run time. You can learn more about binding and data templates in my July

2008 article, " Data and WPF: Customize Data Display with Data Binding and WPF

﴾https://msdn.microsoft.com/magazine/cc700358﴿."

If it were not for the support for commands in WPF, the MVVM pattern would be much less

powerful. In this article, I will show you how a ViewModel can expose commands to a View, thus

allowing the view to consume its functionality. If you aren't familiar with commanding, I recommend

that you read Brian Noyes's comprehensive article, " Advanced WPF: Understanding

Routed Events and Commands in WPF

﴾https://msdn.microsoft.com/magazine/cc785480﴿," from the September 2008 issue.

In addition to the WPF ﴾and Silverlight 2﴿ features that make MVVM a natural way to structure an

application, the pattern is also popular because ViewModel classes are easy to unit test. When an

application's interaction logic lives in a set of ViewModel classes, you can easily write code that tests

it. In a sense, Views and unit tests are just two different types of ViewModel consumers. Having a

suite of tests for an application's ViewModels provides free and fast regression testing, which helps

reduce the cost of maintaining an application over time.

In addition to promoting the creation of automated regression tests, the testability of ViewModel

classes can assist in properly designing user interfaces that are easy to skin. When you are designing

an application, you can often decide whether something should be in the view or the ViewModel by

imagining that you want to write a unit test to consume the ViewModel. If you can write unit tests

for the ViewModel without creating any UI objects, you can also completely skin the ViewModel

because it has no dependencies on specific visual elements.

Lastly, for developers who work with visual designers, using MVVM makes it much easier to create a

smooth designer/developer workflow. Since a view is just an arbitrary consumer of a ViewModel, it

is easy to just rip one view out and drop in a new view to render a ViewModel. This simple step

allows for rapid prototyping and evaluation of user interfaces made by the designers.

The development team can focus on creating robust ViewModel classes, and the design team can

focus on making user‐friendly Views. Connecting the output of both teams can involve little more

than ensuring that the correct bindings exist in a view's XAML file.

The Demo Application

At this point, I have reviewed MVVM's history and theory of operation. I also examined why it is so

popular amongst WPF developers. Now it is time to roll up your sleeves and see the pattern in

action. The demo application that accompanies this article uses MVVM in a variety of ways. It

provides a fertile source of examples to help put the concepts into a meaningful context. I created

the demo application in Visual Studio 2008 SP1, against the Microsoft .NET Framework 3.5 SP1. The

unit tests run in the Visual Studio unit testing system.

The application can contain any number of "workspaces," each of which the user can open by

clicking on a command link in the navigation area on the left. All workspaces live in a TabControl on

the main content area. The user can close a workspace by clicking the Close button on that

workspace's tab item. The application has two available workspaces: "All Customers" and "New

Customer." After running the application and opening some workspaces, the UI looks something

like Figure 1.

Figure 1 Workspaces

Only one instance of the "All Customers" workspace can be open at a time, but any number of "New

Customer" workspaces can be open at once. When the user decides to create a new customer, she

must fill in the data entry form in Figure 2.

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黄汉

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