All You Need to Know about Programming Design patterns

MVC or Model View Controller

• • This framework allows you to build applications which are easier to test and maintain. It consists of three major components which are as follow:

1. Model

It is the layer which represents the data of the application.

2. View

It represents the presentation or primarily called as user interface layer.

3. Controller

It contains the business logic of the application.

• The major objective of this MVC design pattern is to separate concerns in order to facilitate testability. This design pattern allows you to isolate those concerns. It also makes the code of the application easier to test as well as maintain.

• In typical MVC design, the request arrives at the controller. This controller binds the model with the corresponding view. In this design pattern, the view as well as the controller make use of strategy decision. They also view as well as the model are subsequently synchronized using the observer design. Hence, MVC can be called as a compound pattern. The controllers and the view are loosely coupled. One controller is used by multiple views. The view subscribes to the model’s changes.

MVP or Model View Presenter

This design pattern consists of three components- the Model, the View and the Presenter. In this pattern, the controller (in) MVC is replaced by the Presenter. The Presenter here refers back to the view due to which the mocking of view is easier. It also makes unit testing of applications that leverage the MVP design pattern over the MVC design pattern much easier. The presenter in this design pattern changes the model and also make updates in the view. There are two different variations in this design which are as follows:

1. Passive View

In this, the view is not aware of the model. The presenter updates the view in order to reflect the changes in the model.

2. Supervising Controller

Here, the view interacts with the model directly in order to bind the data controls. This is done without the intervention of the presenter. Here, the presenter has to update the model. The presenter changes the view only if it is required especially when you require a complex user interface logic that needs to be executed.

• These two variants promote testability of the presentation logic. However, the passive view variant is preferred because of the testability. It is because you are provided with all the view updated logic within the presenter.

• The MVP design pattern is preferred over MVC only when the application requires to offer support for multiple user interface technologies. It is also preferred when you have a complex user interface where there is a lot of user interaction.

MVVM or Model- View-ViewModel

• This pattern is a refinement of the famous MVC pattern. The ViewModel in MVVM is utilized to facilitate the Presentation Separation. In this design pattern, the logic is stored in the presented. The view is completely isolated from the model. The presenter Isn’t aware of the view but the view is aware of the presenter. The presenter in MVVM is utilized to represent an abstract view of the UI. A passive view means that the view doesn’t have knowledge of the model. In this pattern, the view is active. It consists of behaviors well as events along with data binding information. The ViewModel in MVVM is duly assigned for presentation separation. It also exposes the methods as well as the commands. This is done to manage the view’s state and to change the model.

• The view and the ViewModel in this design pattern communicated by using methods as well as properties and events. This bi-directional data binding between the view and the ViewModel make sure that the models and the ViewModel’s properties are in sync with the view. This design pattern is best for applications which require support for bi-directional data binding.

Viper

This is a design pattern which implements the separation of the concern. Like MVP and MVC, it also follows modular approach with one function, one module. For each module, Viper has mostly four or five various classes each with different roles. No class has more than one sole purpose. These classes are mentioned below:

View

The class which has all the code to showcase the app interface to the user and also gets their response. On receiving the response, the View alerts the Presenter.

Presenter

It gets the user response and works according to it. It’s the only class that communicates with all other different components. It calls the router for wire-framing along with interactor to fetch data and view to update and change the user interface.

Interactor

It has the business logics of the app. It males API calls to fetch the data from the source. It has to make data calls but it is not necessary to do it itself.

Router

It does the wire-framing and listens from the presenter regarding which screen to present and then execute it.

Entity

It consists of model classes used by the interactor.

Conclusion

• The design patterns are an important aspect of application development. It depends on the requirement of the application to decide which design pattern to adopt. Every design pattern has its own advantages. The preference is based on the requirement of the application. Like in case if the application requires to provide support for the multiple user interface technologies, MVP is preferred over MVC. Similarly, if the application requires bi-directional data binding, MVVM is preferred.

• So when it comes to application development, choose the design pattern which you require for implementing various features and functionalities to the application. It is often suggested that the right design pattern delivers the expected goal in time and cost-effective way, without any complication.