Async Event Handling

Last Updated: 5/7/2009

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IW Ajax Limitations
Error Handling and Debugging
Update Protocol
Async Event Handling

Advanced Async Event Handling

Implementing Asynchronous events with IntraWeb is plain and easy. Just hook some Pascal (or C++) code to any of the OnAsync Event handlers and you are done. The Advanced Ajax Events demo shows how to call Async events from your custom JavaScript routines and how to implement an asynchronous Key event handler.

This is all you need to Ajax-enable your IntraWeb application:

procedure TIWForm2.IWButton1AsyncClick(Sender: TObject;  EventParams: TStringList);
begin
  LabelResponse.Caption := 'Hello Ajax World!'
end;

Very simple, but what if you want to call async events from your own custom JavaScript? How to connect key events to some async IntraWeb handler?

This is the Delphi side of an async event handler, that listens to CTRL-A in the Web browser:

procedure TIWForm2.IWAppFormCreate(Sender: TObject);
begin
  WebApplication.RegisterCallBack('OnCtrlA', OnCtrlA);
end;

procedure TIWForm2.OnCtrlA(EventParams: TStringList);
begin
  WebApplication.ShowMessage('You pressed [CTRL - A] - Edit value: ‘+ IWEdit1.Text);
end;

The code in the Form’s JavaScript property implements the JavaScript side and shows how to call a “CallBack” (aka Delphi Async event handler) manually:

function KeyDownHandler(event){
 //Hide for CTRL-A key from browser
 if (event.keyCode==65 && event.ctrlKey)
 {
 event.returnValue = false;
 return false;  }
else {
 return true;
 }};

function KeyUpHandler(event){
 //check for CTRL-A key
 if (event.keyCode==65 && event.ctrlKey) {
   processAjaxEvent(event, null,"OnCtrlA",false, null, true);
   //hide from further "external" handling
   event.returnValue = false;
   return false;
  } else {
    return true;
  } };
//connect event handlers
window.onkeyup = KeyUpHandler;
window.onkeydown = KeyDownHandler;