Call ExtJs function from flash

Can someone help me? i need to call one Extjs function from a button on my flash app.

in flash i put.

Code:

ExternalInterface.call("testExt","Hello from Flex Binhoca!");

With standard JS i can successfully use

Code:

 function testeExt(text){
         alert(text);
        }

How can I declare/call a function the same way on ExtJS ?

My flash app are one item on Prinicpal view (actually I can call a flash fuction from ExtJs).