NavWin Web MVP is a generic MVP (Model-View-Presenter) framework written in C# which specifically implements a popular JavaScript AJAX library (Google Web Toolkit) for the client side view. The original implementation used the Dojo JavaScript library, however the Google Web Toolkit uniquely allows you to develop JavaScript using the strongly typed, compiled Java language in Eclipse. This makes it the most valuable JavaScript development environment available anywhere. It also has the nice feature to create 6 different flavours of your JavaScript, each one optimised for a different popular web browser. This helps your users get a really fast web experience.

Multiple Platforms

The NavWin MVP implements MVP properly, in the sense that each application will work on the web or as a Windows application. In theory you could extend this to any number of mediums (e.g. iPad applications). The Windows version is used to allow fast development of the application (as the ‘compile and run’ turn-around time is much faster than the web equivalent). The Web version is for distribution on the web site.

General concepts

In order to support MVP on the web you need the following basic elements:

1) A concept of model (the logical database)

2) A concept of view (the client side GUI which contains no business logic)

3) A concept of data source (the physical database)

4) A concept of presenter (which ties together the model, the view and the business logic)

5) A concept of a presenter router (Presenter mapping)

6) A concept of location (URL mapping)

The Microsoft Visual Studio environment actually manages to take you some of the way there, as it basically implements a key part of MVP with its segregation of design code and presenter code in every form or user control. This provides a useful starting point to extend to generic, web based MVP.

Communicating with the client

In a web environment, the client is the web browser. In a web environment, all communication between the client and the server is done using Unicode text based messages. Therefore a structured text based notation needs to be defined. This could be a pre-packaged notation, such as JSON, however we have opted for an even more compact notation that allows easy sequential parsing in JavaScript. The idea is to try to make the communication cycle between the client and the server as short as possible to improve the user experience.

Rendering the view in the client

As the view contains no business logic it is actually quite easy to program the client. The client only needs to do 3 things:

1) Process a load message (which defines the control layout and initial data)

2) Process an update message (which defines new data and possibly new control layout)

3) Send an event message (which will include the current state of the control data)

This is why it would be easy to plug in another client (such as iPad) when using MVP.