Monthly Archives: January 2016

Events are fun right? Well, only in part to be honest. For example, what do you do if you want to catch the same event but at different places?

This is where JavaScript’s addEventListener() comes into play. In short it allows you to add as many event-handlers to the same event as your heart desires. But raw unadulterated JavaScript is a bit of a mess, so I decided to wrap this up in clear cut objects. Oh, and I added a “fixed” event for when you want to have objects for standard events as well.

So now whenever you want to hook an event without ruining your published event-handlers (for instance in TW3CustomControl) you can just use one of these 🙂

Enjoy!

unit eventobjs;

interface

uses 
  w3c.dom,
  SmartCL.Components,
  SmartCL.System;

type


  TEventObjTriggeredEvent = procedure (sender:TObject;EventObj:JEvent);

  TEventObj = class(TObject)
  private
    FOwner:     TW3TagObj;
    FAttached:  Boolean;
    FEventName: String;
  protected
    procedure   HandleEvent(eobj:variant);virtual;
  public
    Property    Attached:Boolean read FAttached;
    procedure   Attach(EventName:String);
    procedure   Detach;
    constructor Create(AOwner:TW3TagObj);virtual;
    destructor  Destroy;Override;
  public
    Property    EventName:String read FEventName;
    Property    Owner:TW3TagObj read FOwner;
    Property    OnEvent: TEventObjTriggeredEvent;
  end;

  TFixedEventObj = class(TObject)
  protected
    FAttached:  Boolean;
    FOwner:     TW3TagObj;
    procedure   HandleEvent(eobj:variant);virtual;
  protected
    function    DoGetEventName:String;virtual;abstract;
  public
    Property    Attached:Boolean read FAttached;
    procedure   Attach;
    procedure   Detach;
    constructor Create(AOwner:TW3TagObj);virtual;
    destructor  Destroy;override;
  public
    Property    Owner:TW3TagObj read FOwner;
    Property    OnEvent: TEventObjTriggeredEvent;
  end;

  TElementRemovedEvent = class(TFixedEventObj)
  protected
    function  DoGetEventName:String;override;
  end;

  TElementAddedEvent = class(TFixedEventObj)
  protected
    function  DoGetEventName:String;override;
  end;

implementation


//#############################################################################
// TElementAddedEvent
//#############################################################################

function TElementAddedEvent.DoGetEventName:String;
begin
  result := "DOMNodeInserted";
end;

//#############################################################################
// TElementRemovedEvent
//#############################################################################

function TElementRemovedEvent.DoGetEventName:String;
begin
  result := "DOMNodeRemoved";
end;

//#############################################################################
// TFixedEventObj
//#############################################################################

constructor TFixedEventObj.Create(AOwner:TW3TagObj);
begin
  inherited Create;
  FOwner:=AOwner;
  Attach;
end;

destructor TFixedEventObj.Destroy;
begin
  Detach;
  inherited;
end;

procedure TFixedEventObj.Attach;
begin
  if FAttached then
  Detach;
  FOwner.Handle.addEventListener(DoGetEventName,@HandleEvent,true);
  FAttached := true;
end;

procedure TFixedEventObj.Detach;
begin
  if FAttached then
  begin
    FOwner.Handle.removeEventListener(DoGetEventName,@HandleEvent,true);
    FAttached := false;
  end;
end;

procedure TFixedEventObj.HandleEvent(eObj:variant);
begin
  if assigned(OnEvent) then
  OnEvent(self, JEvent(eObj));
end;

//#############################################################################
// TEventObj
//#############################################################################

constructor TEventObj.Create(AOwner:TW3TagObj);
begin
  inherited Create;
  FOwner := AOwner;
end;

destructor TEventObj.Destroy;
begin
  if FAttached then
  Detach;
  inherited;
end;

procedure TEventObj.HandleEvent(eobj:variant);
begin
  if assigned(OnEvent) then
  OnEvent(self,JEvent(eObj));
end;

procedure TEventObj.Attach(EventName:String);
begin
  if FAttached then
  Detach;

  FEventName := EventName;
  try
    FOwner.handle.addEventListener(FEventName,@HandleEvent,true);
  except
    FEventname:= '';
    FAttached:=false;
    exit;
  end;
  FAttached:=true;
end;

procedure TEventObj.Detach;
begin
  if FAttached then
  begin
    try
      FOwner.handle.removeEventListener(FEventName,@HandleEvent,true);
    finally
      FEventName := '';
      FAttached := false;
    end;
  end;
end;

end.