Developing a Portal using EGL Rich UI - Bending the Laws of Physics
ChrisLaffra 060000KCEQ Comments (10) Visits (6025)
One of the most inspiring video games I have ever seen is the Aperture Science Enrichment Center, also known as Portal. It bends the law of physics in very interesting patterns:
Image/article source: Wired Magazine
Now, I am kind of tricking you, as this is not the kind of Portal this blog entry will discuss. However, I cannot help thinking of this game whenever someone asks me if you can do "portals" in EGL Rich UI.
So seriously, when people ask me about Portals there are asking two different questions:
How to build a client-side Portal?
Our starting point is the GadgetContainer sample that comes with EGL CE and that can be found in the Dojo samples project that EGL CE automatically creates for you:
First step is to reduce that sample to something a bit simpler, and then use other applications (preferably done in EGL Rich UI) to occupy the various portlets.
Here is our most reduced version of our Portal:
This produces a portal with 4 empty portlets:
Now, we will place an iframe into one of the portlets and insert another EGL Rich UI application inside it:
We deployed the second application, in this case Portlet1 in the same location as the main handler, so we use the same base URL to compute the URL for the nested handler. The portlet itself works like a standalone application and can be developed normally using EGL CE. Nothing special is required in its implementation:
The portlets can be dragged around, and here is the result after dragging all the empty ones to the second column:
Now let's add a more interesting portlet, such as one where two portlets communicate with each other. We will use the EGL InfoBus, which is based on the standard OpenAjax Hub to send messages between the portal and its portlets.
Our second portlet shows an entry field and a button. Here is the source:
Notice it is waiting for calculator requests by subscribing to "calculator.result" messages on the InfoBus. Whenever any handler on the current page does a publish with that message key, Portlet 2 will be notified in its "showResult" function. When the user presses Enter or clicks the Go button, a multiplication request is published on the InfoBus again, to be picked up by Portlet 3 (see below).
Our third portlet implements a calculator that multiplies a number with 2. Here is the source:
Again, it defines a subscription to the InfoBus, and handles them in its "calculate" function. Once a result is known, we publish it on the InfoBus again. When something unexpected happens, such as arithmetic overflow or the user enters an invalid number, we print a message.
Finally, portlet 4 simply shows another URL, in this case http://ibm.com/
The end result looks like this:
You may have noticed declarations to the following field in some of the portlets:
What this does is include a fix for InfoBus to allow it to work across iframes. Normally a parent and its nested iframes are completely isolated from each other. What the fix allows for is communication between these two different documents.
What if I don't want a Portal?
The above sample shows how to build a client-side Portal using iframes for the individual portlets and InfoBus for communication. You can use the same technique for other compositions of multiple "modules". One example could be having a main handler with a tab folder. As that is all it contains, it will start up quickly. Then as tabs are opened over time, more and more sub-modules are downloaded on demand (using the above IFrame approach).
The nested handlers can be kept around (as in the Portal), but a different policy could be to do some form of "garbage collection" by unloading the iframes from the document, and recreating them from scratch again when the user likes.
By decomposing modules into separate application level URLs, complexity goes down, individual files get smaller, and things will faster initially and will benefit usage patterns where a limited breath of functionality is actually activated by the end user. Some application have hundreds, even thousands of "screens", and putting them all in one single mega-application makes little sense as during any session only a few dozen may be actually activated.
To try this out in your own workspace, import the attached archive as "General > Existing projects into Workspace". Open the Portal.egl application and load it in the preview.
To try out the non-Portal approach, check out "AppSwitcher.egl".