Event block

The event block of the FORM statement - a set of constructions controlling events in an interactive form view.

Syntax

EVENTS formEventDecl1, ..., formEventDeclN

Where each formEventDecli has the following syntax:

ON eventType eventActionId(param1, ..., paramK) | { eventActionOperator }

Description

The event block allows to define handlers for form events that occur as the result of certain user actions. Each block can have an arbitrary number of comma-separated event handlers. If several handlers are defined for an event, they are guaranteed to be executed in the order they are defined.

Parameters

• eventType

  Type of form event. It is specified with one of the following keywords:

  • INIT
  • OK
  • OK BEFORE
  • OK AFTER
  • APPLY
  • APPLY BEFORE
  • APPLY AFTER
  • CANCEL
  • CLOSE
  • DROP
  • CHANGE objName – specifies that the action will be executed when the object objName is changed.
  • QUERYOK
  • QUERYCANCEL

• eventActionId

  The ID of the action, that will be the event handler.

• param1, ..., paramK

  List of action parameters. Each parameter is specified with the object name on the form. The object name, in turn, is specified with a simple ID.

• actionOperator

  Context-dependent action operator. You can use the names of already declared objects on the form as parameters.

Examples

showImpossibleMessage()  { MESSAGE 'It\'s impossible'; };

posted = DATA BOOLEAN (Invoice);

FORM invoice 'Invoice' // creating a form for editing an invoice
    OBJECTS i = Invoice PANEL // creating an object of the invoice class

//    ...  setting the rest of the form behavior

    EVENTS
        // specifying that when the user clicks OK, an action should be executed 
        // that will execute actions to "conduction" this invoice
        ON OK { posted(i) <- TRUE; },
 
        // by clicking the formDrop button, showing a message that this cannot be, 
        // since this button by default will be shown only in the form for choosing an invoice, 
        // and this form is basically an invoice edit form
        ON DROP showImpossibleMessage() 
;

CLASS Shift;
currentShift = DATA Shift();

CLASS Cashier;
currentCashier = DATA Cashier();

CLASS Receipt;
shift = DATA Shift (Receipt);
cashier = DATA Cashier (Receipt);

FORM POS 'POS' // declaring the form for product sale to the customer in the salesroom

    OBJECTS r = Receipt PANEL // adding an object that will store the current receipt

    //  ... declaring the behavior of the form
;

createReceipt ()  {
    NEW r = Receipt {
        shift(r) <- currentShift();
        cashier(r) <- currentCashier();

        SEEK POS.r = r;
    }
}

// adding a property through the form extension so that SEEK could be applied to the already created
// object on the form
EXTEND FORM POS 
    EVENTS
        // when opening the form, executing the action to create a new receipt, 
        // which fills in the shift, cashier and other information
        ON INIT createReceipt() 
;