R – Create instances of flex custom component by passing in type

actionscript-3apache-flexmxml

In my flex app there are a few custom components. I want to create instance of these components at runtime and assign them properties by reading in a config file.
I know how to read xml and instantiate components, however my question is about being able
to get the type of the component from the xml attribute and then creating an instance of that type.
My xml looks like this:

Best Answer

You can instantiate an arbitrary named type through ActionScript's "reflection API":

var clazz:Class = Class(getDefinitionByName("class.from.your.xml.file.Name"));
var component:Object = new clazz();

http://livedocs.adobe.com/flex/3/langref/flash/utils/package.html#getDefinitionByName()

If you get an error about the type not existing, this is because it isn't linked from elsewhere in your application and the compiler only adds classes that are referenced. You can work around this using the following compiler arg:

includes class [...]

Links one or more classes to the resulting application SWF file, whether or not those classes are required at compile time.

http://livedocs.adobe.com/flex/3/html/compilers_14.html#157203

Related Solutions

R – Flex application to component

The easy thing to do is to swap the Application mxml tag with a VBox tag...thus making it act like a component.

e.g. If this were your application:


//Foo.mxml
<mx:Appliction xmlns:mx="http://www.adobe.com/2006/mxml">
    <mx:Label text = "foo" />
</mx:Appliction>

change it to:


//Foo.mxml
<mx:VBox>
    <mx:Label text = "foo" />
</mx:VBox>

and then you can do something like this:


//App.mxml
<mx:Appliction 
    xmlns:mx="http://www.adobe.com/2006/mxml"
    xmlns:local="your.package.scheme.*"
>
    <local:Foo />

</mx:Appliction>

You may have to make some public properties if you need to pass in any data to the component...

R – Flex app architecture, how can I build component library that can be overridden

You could solve the problem by using a class factory. Instead of creating instances of new components directly, you would ask a factory class to create the component for you, and based on some criteria (perhaps a static constant value in the Application?) the factory would decide which class to instantiate the component from.

The article and code sample on Wikipedia explains it better than I ever could: Factory method pattern (read on from the "Encapsulation" heading).

Two potential drawbacks with this approach:

You will be adding more architecture to your codebase. In my experience the factory pattern doesn't necessarily make code easier to read. Difficult to read code == less reusable code.
If you rely heavily on MXML you might need even more quirks to instantiate the components from the factory.

Best Answer

Related Solutions

R – Flex application to component

R – Flex app architecture, how can I build component library that can be overridden

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