Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Design > Adobe Creative Suite

From Flash to Flex: Understanding Flex Events

📄 Contents

  1. Event Dispatching
  2. Event Dispatching
Events drive and breathe life into Flex applications, so understanding them is crucial to Flex development. In the latest article in the "From Flash to Flex" series, Kris Hadlock explains Flex events and how to incorporate them into object-oriented code.
Like this article? We recommend

Like this article? We recommend

Everything in Flex occurs based on an event. This means that simply clicking a button or key to moving the mouse or receiving a response from a web service provides developers with the ability to trigger a custom event in their Flex applications. That’s a lot of control, and since Flex is not based on the request/response model of a standard web app, the app contains the functionality to perform those custom events without ever leaving the web page. This is because events are client-based—in other words, separated from the request/response model of a web page and do not require the page to refresh with every user interaction.

On the Web a Flex app is completely loaded upfront, which allows the functionality within to respond faster than a standard web request model. This will initially cause the user to wait until the app is fully loaded, but will save time when it counts, which is during usage.

Not having to wait for a page refresh also prevents the user from having problems maintaining context because the screen reacts instantaneously. With these additional benefits you would expect some new issues to arise, but the capabilities of Flex are not limited in any way when comparing them with a standard web app.

In this article you will learn how to leverage the power of events by dispatching them in your own custom classes. The source code for this project can be downloaded here.

If you feel you need some background on Flex development before diving into events, take a look at the previous articles in the From Flash to Flex series.

Event Dispatching

Dispatching your own events starts by extending the UIComponent. In the last article of the Flash to Flex series, "Creating ActionScript Components for Flex," I explained how to create a Flex component by extending the UIComponent.

This article will pick up where that article left off by adding the additional functionality to dispatch your own custom events when a headline is selected. As a quick recap, the headline component that we built ran from XML, which defined a URL and display text for different headlines. When the app loaded, the component would cycle through each of the headlines for a predetermined interval that we passed to the constructor. Each headline would display at the top of the page waiting for someone to click it and visit the corresponding URL.

Since the UIComponent extends the EventDispatcher, all subclasses of the UIComponent have access to the dispatchEvent() method.

Relying on the href to link us to the URL of a headline works great, but if we wanted to add some additional functionality each time a headline is selected, such as logging what headlines were selected and at what time, this functionality would not allow it.

Therefore we will use events to inform a custom handler of the selection and then we will dispatch an event and delegate it to the appropriate class, which will log the data that we define.

First of all, we need to change the way that our headlines are constructed to trigger an event in the href (see Listing 1) instead of just linking to the URL as we did before (see Listing 2).

Listing 1: Triggering an event

this.headlines.push("<a href=’event:"+ _headlines[i].attribute("action") +"’>"+ _headlines[i].text() +"</a>");

Listing 2: Simply linking to the URL

this.headlines.push(’<a href="’+ _headlines[i].attribute("action") +’" target="_blank">’+ _headlines[i].text() +’</a>’);

If you have developed with Flash, the first thing that you’ll probably notice in Listing 1 is that we are not using asfunction any more; there is now a way to trigger an event from an href.

Now that we have our event in place we need to add a listener to the textfield that we are creating to display the headlines.

To do this I have added the event listener to the createTextField method from our previous headline class and modified it a bit to handle the text directly as a parameter rather than assigning it after the field has been created (see Listing 3).

Listing 3: Adding an event listener

private function cycle(index:Number):void
{
   if(this.currentTextField != null) removeChild(this.currentTextField);
   this.currentTextField = this.createTextField(0, 0, 200, 100, this.headlines[index]);

   if(index == (this.headlines.length-1)) index = 0;
   else index++;

   if(this.__cycleTimeout != 0) clearTimeout(this.__cycleTimeout);
   this.__cycleTimeout = setTimeout(cycle, (this.delay*1000), index);
}

private function createTextField(x:Number, y:Number, width:Number, height:Number, text:String):TextField
{
   var format:TextFormat = new TextFormat();
   format.font = "Arial";
   format.color = 0x333333;
   format.size = 21;
   format.underline = true;

   var txtField:TextField = new TextField();
   txtField.x = x; txtField.y = y;
   txtField.width = width; txtField.height = height;
   txtField.autoSize = "left";
   txtField.defaultTextFormat = format;
   txtField.htmlText = text;
   txtField.addEventListener(TextEvent.LINK, onHeadlineSelected);

   addChild(txtField);
   return txtField;
}

In the createTextField method we added the event listener after the field has been created and assigned the value of the headline. Let’s not forget to include the appropriate class (see Listing 4).

Listing 4: Importing the TextEvent

import flash.events.TextEvent;

Now that our event is being listened to, the next step is to handle it. We will need to create an onHeadlineSelected method to correspond to the event that we defined previously (see Listing 5).

Listing 5: Handling the event

private function onHeadlineSelected(e:TextEvent):void
{
   var u:URLRequest = new URLRequest(e.text);
   navigateToURL(u, "_blank");

   e.currentTarget.addEventListener("textlink", Logger.GetInstance().Log);

   var tev:TextEvent = new TextEvent("textlink", false, false);
   var date:Date = new Date();
   tev.text = date.toString() +"::"+ e.text;
   e.currentTarget.dispatchEvent(tev);
}

If you are transitioning from Flash you’ll notice that there is no longer a getURL method. Instead we need to create a new URLRequest from our URL and then use it in the navigateToURL method, which allows us to target the browser window just as getURL did.

The next line assigns an event listener to a method called Log in a new class called Logger, which we will create in a moment (see Listing 6).

You’ll also notice that we are providing the listener with a custom type called textlink, which will prevent any recursion issues when our other events are fired.

Once we have the listener in place we need to create a new event, which in this case is a TextEvent, set the values that we want to pass the new method and finally dispatch the event to whomever is listening.

Now that we are finally dispatching events, let’s take a look at how to handle them from other classes.

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email ask@peachpit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.peachpit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020