MVC vs MVP vs MVVM for mobile app development: Let's end the debate!

 

modular mvvm applications

A while ago I began to write a blog tutorial about how to create a modular WPF application using MVVM and MEF. I have decided to present it as a screencast instead, so here is the first part. It uses WPF, but a lot of the techniques I show apply equally well to Silverlight. Find helpful customer reviews and review ratings for Developer’s Guide to Microsoft Prism 4: Building Modular MVVM Applications with Windows Presentation Foundation and Microsoft Silverlight (Patterns & Practices) at fitcenterru.cf Read honest and unbiased product reviews from our users. Developer's Guide to Microsoft Prism 4: Building Modular MVVM Applications with Windows Presentation Foundation and Microsoft Silverlight (Patterns & Practices) [Bob Brumfield, Geoff Cox, David Hill, Brian Noyes, Michael Puleio, Karl Shifflett] on fitcenterru.cf *FREE* shipping on qualifying offers. This guide provides everything you need to get started with Prism and to use it to create flexibleReviews:


Screencast: Modular WPF with MEF & MVVM Tutorial Part 1


The Xamarin. Forms developer experience typically involves creating a user interface in XAML, and then adding code-behind that operates on the user interface. As apps are modified, modular mvvm applications, and grow in size and scope, complex maintenance issues can arise. These issues include the tight coupling between the UI controls and the business logic, which increases the cost of making UI modifications, modular mvvm applications, and the difficulty of unit testing such code.

Maintaining a clean separation between application logic and the UI helps to address numerous development issues and can make an application easier to test, maintain, and evolve. It can also greatly improve code re-use opportunities and allows developers and UI designers to more easily collaborate when developing their respective parts of an app. There are three core components in the MVVM pattern: the model, modular mvvm applications, the view, and the view model.

Each serves a distinct purpose. Figure modular mvvm applications the relationships between the three components. In addition to understanding the responsibilities of each component, it's also important to understand how they interact with each other. At a high level, the view modular mvvm applications about" the view model, modular mvvm applications, and the view model "knows about" the model, but the model is unaware of the view model, and the view model is unaware of the view.

Therefore, the view model isolates the view from the model, and allows the model to evolve independently of the view. The key to using MVVM effectively lies in understanding how to factor app code into the correct classes, and in understanding how the classes interact. The following sections discuss the responsibilities of each of the classes in the MVVM pattern.

The view is responsible for defining the structure, layout, and appearance of what the user sees on screen. Ideally, each view is defined in XAML, with a limited code-behind that does not contain business logic. However, modular mvvm applications, in some cases, the code-behind might contain UI logic that implements visual behavior that is difficult to express in XAML, such as animations.

In a Xamarin. Forms application, a view is typically a Page -derived or ContentView -derived class. However, views can also be represented by a data template, which specifies the UI elements to be used to visually represent an object when it's displayed. A data template as a view does not have any code-behind, and is designed to bind to a specific view model type.

Avoid enabling and disabling UI elements in the code-behind. Ensure that view models are responsible for defining logical state changes that affect some aspects of the view's display, modular mvvm applications, such as whether a command is available, or an indication that an operation is pending.

Therefore, enable and disable UI elements by binding to view model properties, rather than enabling and disabling them in code-behind. There are several options for executing code on modular mvvm applications view model in response to interactions on the view, such as a button click or item selection.

If a control supports commands, the control's Command property can be data-bound to an ICommand property on the view model. When the control's command is invoked, the code in the view model will be executed. In addition to commands, behaviors can be attached to an object in the view and can listen for either a command to be invoked or event to be raised.

In response, the behavior can then invoke an ICommand on the view model or a method on the view model. The view model implements properties and commands to which the view can data bind to, and notifies the view of any state changes through change notification events, modular mvvm applications. The properties and commands that the view model provides define the functionality to be offered by the UI, but the view determines how that functionality is to be displayed.

Keep the UI responsive with asynchronous operations. Mobile modular mvvm applications should keep the UI thread unblocked to improve the user's perception of performance. The view model is also responsible for coordinating the view's interactions with any model classes that are required.

There's typically a one-to-many relationship between the view model and the model classes. The view model might choose to expose model classes directly to the modular mvvm applications so that controls in the view can data bind directly to them. In this case, the model classes will need to be designed to support data binding and change notification events. Each view model provides data from a model in a form that the view can easily consume.

To accomplish this, the view model sometimes performs data conversion. Placing this data conversion in the view model is a good idea because it provides modular mvvm applications that the view can bind to. For example, the view model might combine the values of two properties to make it easier for display by the view. Centralize data conversions in a conversion layer.

It's also possible to use converters as a separate data conversion layer that sits between the view model and the view. This can be necessary, modular mvvm applications, for example, when data requires special formatting that the view model doesn't provide.

In order for the view model to participate in two-way data binding with the view, its properties must raise the PropertyChanged event. View models satisfy this requirement by implementing the INotifyPropertyChanged interface, and raising the PropertyChanged event when a property is changed.

This collection implements collection changed notification, relieving the developer from having to implement the INotifyCollectionChanged interface on collections. Model classes are non-visual classes that encapsulate the app's data. Therefore, the model can be thought of as representing the app's domain model, which usually includes a data model along with business and validation logic.

Model classes are typically used in conjunction with services or repositories that encapsulate data access and caching. View models can be connected to views by using the data-binding capabilities of Xamarin. There are many approaches that can be used to construct views and view models and associate them at runtime. These approaches fall into two categories, known as view first composition, and view model first composition.

Choosing between view first composition and view model first composition is an issue of preference and complexity.

However, all modular mvvm applications share the same aim, which is for the view to have a view model assigned to its BindingContext property. With view first composition the app is conceptually composed of views that connect to the view models they depend on.

The primary benefit of this approach is that it makes it easy to construct loosely coupled, unit testable apps because the view models have no dependence on the views themselves. It's also easy to understand the structure of the app by following its visual structure, rather than having to track code execution to understand how classes are created and associated.

In addition, view first construction aligns with the Xamarin. Forms navigation system that's responsible for constructing pages when navigation occurs, which makes a view model first composition complex and misaligned with the platform. With view model first composition the app is conceptually composed of view models, with a service being responsible for locating the view for a view model.

View model first composition feels more natural to some developers, since the view creation can be abstracted away, allowing them to focus on the logical non-UI structure of the app. In addition, it allows view models to be created by other view models. However, this approach is often complex and it can become difficult to understand how the various parts of the app are created and associated.

Keep view models and views independent. The binding of views to a property in a data source should be the view's principal dependency on its corresponding view model, modular mvvm applications. Specifically, don't reference view types, such as Button and ListViewfrom view models.

By following the principles outlined here, view models can be tested in isolation, therefore reducing the likelihood of software defects by limiting scope. The simplest approach is for the view to declaratively instantiate its corresponding view model in XAML.

When the view is constructed, modular mvvm applications, the corresponding view model object will also be constructed. This approach is demonstrated in the following code example:, modular mvvm applications. This declarative construction and assignment of the view modular mvvm applications by the view has the advantage that it's simple, but has the disadvantage that it requires a default parameter-less constructor in the view model.

A view can have code in the code-behind file that results in the view model being assigned to its BindingContext property. This is often accomplished in the view's constructor, as shown in the following code example:. The programmatic construction and assignment of the view model within the view's code-behind has the advantage that it's simple. However, the main modular mvvm applications of this approach modular mvvm applications that the view needs to provide the view model with any required dependencies.

Using a dependency injection container can help to maintain loose coupling between the view and view model. For more information, see Dependency Injection. A view can be defined as a data template and associated with a view model type.

Data templates can be defined as resources, or they can be defined inline within the control that will display the view model. The content of the control is the view model instance, and the data template is used to visually represent it.

This technique is an example of a situation in which the view model is instantiated first, modular mvvm applications, followed by the creation of the view. A view model locator is a custom class that manages the instantiation of view models and their association to views, modular mvvm applications.

In the view's XAML, this attached property is set to true to indicate that the view model should be automatically connected to the view, as shown in the following code example:. This method resolves the view model for the view. The following code example shows how this is achieved:.

This convention assumes that:. For more information about resolving the view model type, see Resolution. Modular mvvm applications approach has the advantage that an app has a modular mvvm applications class that is responsible for the instantiation of view models and their connection to views. Use a view model locator for ease of substitution. A view model locator can also be used as a point of substitution for alternate implementations of dependencies, such as for unit testing or design time data.

All view model and model classes that are accessible to a view should implement the INotifyPropertyChanged interface. Implementing this interface in a view model or model class allows the class to provide change notifications to any data-bound controls in the view when the underlying property value changes. Apps should be architected for the correct use of property change notification, by meeting the following requirements:. The eShopOnContainers mobile app uses the ExtendedBindableObject class to provide change notifications, which is shown in the following code example:.

The ExtendedBindableObject class provides the RaisePropertyChanged method to invoke property change notification, and in doing so uses the functionality provided by the BindableObject class.

Therefore, modular mvvm applications, each view model class uses the RaisePropertyChanged method in the ExtendedBindableObject class to provide property change notification.

The following code example shows how the eShopOnContainers mobile app invokes property change notification by using a lambda expression:. Note that using a lambda expression in this way involves a small performance cost because the lambda expression has to be evaluated for each call.

 

mvvm - Framework for modular WPF application? - Stack Overflow

 

modular mvvm applications

 

Find helpful customer reviews and review ratings for Developer’s Guide to Microsoft Prism 4: Building Modular MVVM Applications with Windows Presentation Foundation and Microsoft Silverlight (Patterns & Practices) at fitcenterru.cf Read honest and unbiased product reviews from our users. Dec 02,  · However, even without using any third party UI control, the steps below can be used to develop a modular UI application with WPF and Prism and by using regular WPF controls. The purpose of this example is to show the basic steps to start a modular application using Prism/Unity and not the usage of third party controls. A while ago I began to write a blog tutorial about how to create a modular WPF application using MVVM and MEF. I have decided to present it as a screencast instead, so here is the first part. It uses WPF, but a lot of the techniques I show apply equally well to Silverlight.