Flex (Learning Flex 3 Book) : Removing IEventDispatcher error from the DataGrid

When I decided to learn Flex I started with Learning Flex 3. It's a great book and does an excellent job of introducing the MXML framework and Flex Builder IDE. I would recommend it to anyone.

One of the problems I have with the book is it doesn't teach you how to remove warnings from your code. A later code example produces the following error: warning: unable to bind to property 'contact' on class 'XML' (class is not an IEventDispatcher). It's not a big deal, but I like to write code that doesn't produce hidden errors.

Here is the code from the book:

<mx: Application
    xmlns: mx="http: //www.adobe. com/2006/mxml"
    xmlns: view="com.oreilly.view.*"
    layout="absolute"
    applicationComplete="contactsService.send()" >
    <mx:HTTPService id="contactsService"
        resultFormat="e4x"
        url="contacts.xml" />
    <mx:DataGrid id="contactsDataGrid"
        dataProvider="{contactsService.lastResult.contact}"
        selectedIndex="0"
        left="10"
        top="10"
        bottom="10"
        width="300">
        <mx: columns>
            <mx: DataGridColumn headerText="First"  
            dataField="firstName"/>
            <mx: DataGridColumn headerText="Last" dataField="lastName"/>
        </mx:columns>
    </mx:DataGrid>
    <view: ContactViewer
        contact="{contactsDataGrid. selectedItem}"
        x="318" y="10">
    </view: ContactViewer>
</mx: Application>

The problem is the dataProvider property of DataGrid. It's unable to figure out how to parse the data, so it throws a warning. This can be resolved with casting. We can tell the dataProvider what it should be and it will remove the warning. Here is the code that will remove the warning.

dataProvider="{XMLList(XML(contactsService.lastResult).contact)}"

contactsService.lastResult is an XML object. There are multiple children in the object. We can then cast the XML object as an XMLList to use contact child node.

Feel free to leave a comment if you have any questions.

Flex: New Classes won't import into a project from a library

I ran into an issue while working on a Flex project where a new class I created in a Library wouldn't import, or auto-complete in the working project. It was also throwing a few different errors.

This was displayed at Runtime:
Variable xxx is not defined.

This was displayed in the Problems window:
Access of undefined property xxx.

Sometimes Flex doesn't update the Build Path to include new classes. If you run into this issue you can check to see if everything in your project is included in the Build Path.

Right-click on your Library project and goto Properties. Select "Flex Library Build Path" on the left and look in the Classes tab on the right. Scroll through the list to make sure everything is selected. If you're getting the errors above there is more than likely something in the list that isn't checked.

Flex: using mxml files as classes

Another thing I learned while working with Flex is that each MXML file can be treated like a class. You can import them and call the functions defined within like a method. This can be very useful when loading element into the stage.

It's also important to note that methods and properties are available once you've created the object. If you have defined something to run on creationComplete it won't run until the object is added to the stage with addChild.

main.mxml

 
        import util.Example;
   private function init() : void {
    var example:Example = new Example;
    
    //run function from external MXML file
    example.example_function();
    
    //add the mxml file to the stage
    addChild(example);
   }
  ]]>
 

util/Example.mxml

 
     public function example_function() : void {
    trace('running function example');
   }
   
   private function init() : void {
    trace('now all the elements inside are available');
   }
  ]]>