What exactly happens in controller???

Hi ,

I am new to web dynpros.now I am developing the Webdynpro application for the Creating the POC(Purchase order creation).So before that I was going trogh the example "Accessing ABAP Functions in Web Dynpro (4)" in sdn.sap.com.I didn/t understood the following code in the controller Like why is he creating an input node.And Kindly even mention what are the methods to be implemented for the transaction application for eg.Purchase Order creation.

public void wdDoInit()

{

//@@begin wdDoInit()

// Create a new element in the Bapi_Flight_Getlist_Input node

Bapi_Flight_Getlist_Input input = new Bapi_Flight_Getlist_Input();

wdContext.nodeBapi_Flight_Getlist_Input().bind(input);

// Create new elements in the Destination_From and Destination_To nodes

input.setDestination_From(new Bapisfldst());

input.setDestination_To(new Bapisfldst());

//@@end

}

public void executeBapi_Flight_Getlist_Input( ) {

//@@begin executeBapi_Getlist_Input()

try

{

// Calls remote function module BAPI_FLIGHT_GETLIST

wdContext.currentBapi_Flight_Getlist_InputElement().modelObject().execute();

// Synchronise the data in the context with the data in the model

wdContext.nodeOutput().invalidate();

}

catch (Exception ex)

{

// If an exception is thrown, then the stack trace will be printed

ex.printStackTrace();

}

//@@end

}

Thanks,

Kumar.