Pearls of Flex: June 2009

Friday, June 19, 2009

Tweaking OLAPCell and OLAPDataGrid to display custom formatted values

Displaying custom formatted data in OLAPDataGrid is a bit tricky because OLAPDataGrid doesn't use the OLAPCell.formattedValue at all due to a bug in its implementation.

However the tweaks I am going to mention are simple and can be used to get this to work. After the tweaks don't forget to build the datavisualization.swc using the steps I have described in one of the earlier posts.

Modifing OLAPCell.as file : Modify the constructor to set a formatted value into the _formattedValue property

public function OLAPCell(value:Number, formattedValue:String=null)

{

_value = value;

_formattedValue = insert any custom formatting logic using value ;

}

Modify OLAPDataGrid.as : Somewhere around line 769 we can find the following line

label = cell && !isNaN(cell.value) ? String(cell.value) : defaultCellString;

Modify this to read as follows

label = cell && !isNaN(cell.value) ? String(cell.formattedValue) : defaultCellString;

Build the swc and use it in your app to get custom formatting. Of-course some more tweaking it required to make this generic and supply a Flex formatter directly to OLAPDataGrid. I am sure it can be easily figured out !

Monday, June 8, 2009

CallResponders explained..

Here is some explanation about CallResponders by Tom Lane. I thought this would be useful to many developers who want to understand more about them so that it becomes easy to work with them.

"Let me take a shot at explaining asynchronous calls. Most PHP developers are used to calling functions in one way only: synchronously. In ActionScript a sychronous function call looks like this:

var stuff = getStuff();

Pretty straightforward. It's how you expect functions to work: you call them, and then immediately on line #2 of this example you have a value in the stuff variable to work with.

But when it comes to calling remote functions on services sitting on a server somewhere, Flex calls them asynchronously. This is so that the Flex client can continue working while the request is pending. An aync call looks more like this (at least, the first part):

responder.token = getStuffFromService();

What this means is, "stuff" does not come back right away as the result of the function. Instead, what it returns is a kind of ticket. Sort of like ordering some food from a lunch counter and getting a receipt with a number on it. You don't get your food right away. Instead, you go hang out or do some other stuff while your order is pending, and then your number is called when it's ready. And then you "respond" to your number.

Well, that's what a CallResponder is. When you "place your order", you hook up a CallResponder to it. When your order is ready (data comes back from the service call), the responder kicks into action. It fires a result event (or a fault if something went wrong), and it updates its bindable lastResult property.

So, if you want to work with data from an async call, you can't simply do it on line #2 of the above snippet. You have to wait until the CallResponder for that call gets its result. If you create a databinding to lastResult, that will automatically update when the result is ready. But since you want to run some script on the result, you have to trigger that script from the CallResponder's result event handler.

Hope this helps!

Saturday, June 6, 2009

Showing different icons in each cell of OLAPDataGrid based on the cell value

I have been getting few queries on how to show different icons based on the cell value in a OLAPDataGrid.

Here is a screen shot of how it looks:

Here are the source files.

The technique is simple. Create a custom itemRenderer which can display a icon and text or anything to suite your needs. Make sure it implements the IDropInListItemRenderer interface. In the setter of listData add the logic to change the icon based on the value. Set this as itemRenderer of the OLAPDataGrid.

The sample shows this using a renderer derived from Canvas with a image control and embedded image files. You can use other light weight techniques like coloring a sprite and using UIComponent as base. If you are adventurous you can try tweaking or deriving from OLAPDataGridItemRenderer itself.