Last week I attended the Microsoft TechDays
2012 at Brussels, and it becomes clear that with the introduction of Windows 8
the future is uncertain about using
plug-ins (Silverlight and Flex) in web browsers.
In Windows 8 Microsoft makes the development with JavaScript with HTML5 a first
class development platform that will be covered in Visual Studio 2011.
In the Silverlight framework I used the
MVVM pattern together with PRISM to use the patterns IoC and DI. The Silverlight application was a somewhat
light ArcGis desktop based on dynamically adding and editing layers based on
new technology introduced in the version 10. I also illustrated how you can add
some advanced editing functionality in an easy way.
In the JavaScript application that I
introduce, I will start from the same application functionality allowing
dynamic map to be used and feature editing on an ArcGis server.
The requirement for this applications will
be as followed:
·
Configuration: The basic configuration
file used is exactly the same as for the Silverlight application. That means I
will use an XML file that will contain all the configuration data for the
application. However a REST service will be used to expose the contents as a
JSON object to the client. Secondary XML
configuration files will also be exposed as JSON objects. I use WCF services in
.NET that will take into account this transformations. You can do the same in JAVA
or create the JSON files yourself before using them at the client side.
·
Libraries: To make programming in
JavaScript a lot easier, some important libraries will be used to help the conversion
of some Silverlight patterns into JavaScript:
o
JQuery: This important library will be
used as support for handling of the DOM and some utility functions.
o
KnockoutJS: This library will handle the
MVVM. Because a lot of the Silverlight application is based on the use of MVVM,
this will make the transitions of the viewmodels a lot easier.
·
GIS classes: The core of the Silverlight
application consists of services that are implemented using Silverlight Classes
and encapsulate the ArcGis Silverlight API functionality. The ArcGis JavaScript API consist of the same
functionality of the Silverlight API because a lot of functionality is based on
the REST services at the ArcGis Server. Converting these services in JavaScript classes is a lot simplified because
of the almost one to one relation in functionality. The GIS classes will be
split into different JavaScript files.
·
Components: In the JavaScript
application, the notion of separate components is not used. The whole
application will be implemented on one HTML page. The viewmodels are
implemented in separate JavaScript files. There will be communication mechanism
used between different viewmodels. In Silverlight I used the eventaggregator
class of the Prism framework, in JavaScript I create an equivalent of this
functionality (publish and subscribe of events).
·
Bootstrapper: An important role was
attributed to the bootstrapper class of the PRISM framework. In JavaScript I will
use the ready function of JQuery to achieve this pattern. The bootstrapper will
be responsible for the creation of all GIS and non-GIS objects used in the
application by using some kind of IoC.
·
HTML page: The idea is to have a page
with very little JavaScript code embedded on the page as I did with the
Silverlight application. Doing so, you can change the look and feel without
having to change something in the viewmodel code or in the GIS classes. By
limiting the creative construction of a HTML page, it is much easier supporting
all kind of web enabled devices.
The application architecture should look similar
to the next picture.
This is the road book for the development
of a JavaScript implementation of a simple ArcGis Desktop application for
viewing an editing of GIS data. In the next document I will show you the
creation of the map with a legend using the above architecture.
