Wednesday, December 10, 2008

Flash Catalyst Tutorial: Weather Widget, Part 4

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In Part 4 of our Adobe Flash Catalyst Tutorial, we'll add some data to the project so that our application can represent a real data set. We wont actually be connecting to an data service for the weather, but you can see how the data would be structured to do so.

We'll be focusing on two things in Gumbo: creating a 'model' for our data, applying and binding the information in our model to our interface elements.

We're using a very loose implementation of a design pattern in our example application called the "model, view, controller" pattern or simply MVC. You may have heard of this in regards to RIA (Rich Internet Application) development before. What this means in simple terms is that we will be separating our code into sections that represent the model (data), view (interface stuff) and controller (event handlers, functions, logic, etc). By breaking the code up into these groups and having the groups or 'packages' organized, we will be creating a structure that allows us to easily edit elements without disturbing or breaking pieces that work - ie. changing interface elements without affecting the functions behind them.

Here are the steps I've taken to get to the latest version of the project.

In Adobe Flex 'Gumbo':

  • Import the .fxp project
  • Go to File > New > ActionScript Class

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  • fill in the appropriate information into the form

You should now have a new class document named 'WeatherDataModel'. We'll be creating a singleton - a class that has one and only one instance - for this class. We do this so that we have one point of contact for our data in the application.

The function 'getInstance()' allows us to access this class from anywhere in our application by stating:


Nice! Next we'll add an actual data set to use. We'll define an XML document as our data source, but you could easily adjust this to any data type you'd like.

Now we have a data model with actual data in it. Lets move on to binding this data to our view. Open the cityComponent.mxml file. We are going to add some code to the Script tag:

Notice how simple it is to reference the model now! We bind the model's data to our visual elements toward the bottom of the page. Move down the file until you see the code for the TextGraphics in the 'current' Group. We'll adjust the parameters to the following:

When we use the curly braces in a parameter like this:

text="{[model.currentCity].name }"

we are binding the information to this view. If the information changes, the view updates. In this case, we defined 'model' as our WeatherDataModel. model.cityData points to the XML that we've defined in the model and then we traverse the XML tree to get the value we'd like to display.

Now we need to display the day and the hi and low for each day in our list below the current weather. Move down a few rows in the cityComponent.mxml document to the list of 7 component:dayComponent nodes. These represent the 7 day forecast list. We'll adjust that code to the following:

We've just bound each of the dayComponents to the same data model! If you save all your files and test the application, you should now see something like this:

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Our application now has 'real' data bound to the interface elements. Stay tuned for more Adobe Flex Catalyst and Flex Gumbo goodness!

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