Introduction:

This article describes a quick and easy approach to playing sound files on  an ASP.NET web page in response to an event.  The approach is based upon an included web custom control used to embed the sound into the web page; this control exposes a sound file path property that may be used to change the associated sound file between postbacks and in response to events fired from the web page.

The web custom control included with this article is compatible with Internet Explorer and Firefox; it has not been tested against any other browsers.  Aside from providing a demonstration of playing sounds in response to events, the included source code does provide an easy example of embedding objects in web pages by means of a web custom control; as such, the example could be used as the basis for creating other controls used to embed other types of objects into a web page.

Getting Started:

In order to get started, unzip the included source code.  Within the zip file you will note that there are two separate projects, one is the custom control itself and the other is a test website used to demonstrate the use of the control.  Create a virtual directory for the website and then open the web custom control library into the Visual Studio 2005 IDE.  If the solution does not open with the website, add the website to the solution.

The Code:  The Custom Web Control Library Project.

Within the custom web control library project (MakeNoise) you will note that there is a single custom control included (PlayPageSound.vb).  Open the class and take a look at the code; the class imports and definition were all left in their default configuration.  After the class declaration, you will note the following code in the initialization event:

This initialization code is used to set the control to 24 pixels by 24 pixels; this does not serve any purpose at runtime however at design time it provides the programmer with a box that they can click on if they need to get access to the control's properties.  It is not necessary to set the box to this size, it is only done to make it easier to manage the control at design time.  At runtime the control will not be visible to the user.

Following the initialization, the one and only property in the control is established.  The property added used to set the path to the sound file; that code looks like this:

Note that the Sound File path is set and retrieved from view state.  The attributes at the beginning of the property declaration are used to set the text in the property grid for both the category and the description areas.

The only remaining code in the control is used to establish how the page will render the control at runtime; again this is very simple and the code looks like this:

The overridden Render Contents subroutine uses a string builder to piece together the code used to embed the sound into the page.  In this instance, only the string pointing to the location of the sound file is changed based upon the current contents of the Sound File property; however, using this same approach one could add other properties such a Loop, Visible, Auto-start, Height and Width and then set them in a manner consistent with what is shown here for setting the sound file property.  Given this configuration, the control will not display a visible UI during the sound's playback.  If one were to set the control to be visible and then give some height and width dimension, the control will display a media player interface to the user whenever the sound is playing.  If the UI were made visible, in Internet Explorer, the Microsoft Media Player control's interface would be displayed, in Firefox, the Quick Time player interface would be shown.

Once the emded tag is created, the  HTML Text Writer is used to place the embed tag within a div.  If anything were to go wrong and an exception was thrown, the catch block will capture the exception and  the HTML Text Writer is then used to write the name of the control onto the page.

The Code:  The Test Web Site.

Open up the test web site; notice that the site consists of a single web page (default.aspx).  The site is setup to simulate an online test; to that that end, the page displays three questions to the user, keeps track of the number of correct responses, and displays messages to the user whenever the user answers a question correctly or incorrectly, and it plays a sound whenever the user gets an answer correct and a different sound whenever the user misses the answer.

This web page contains a single instance of the Play Page Sound custom control.  Depending upon whether or not a user clicks on the right answer or the wrong answer, the control's Sound Path property is set to play the appropriate sound.  Each radio button list (used to show the user the answer options) has its AutoPostBack property set to true so that the correct sound will load and play in response to the user's selection.  If you did not set the AutoPostBack property to true, the sound would not play until some other event called a post back.

Take a quick look at the handler associated with an selected index changed to one of the radio button lists:

End Sub

In this instance, the third answer in the list is correct and the other three options are incorrect.  Whenever the user selects the correct response, the Play Page Sound control's Sound File property is set to a wave file called "applaus8.wav".  In all other options, the Sound File property is set to a wave file called "burp.wav".  After setting the sound to point at the correct wave file, a call is made to a subroutine called, "EvaluateResponses()".  This subroutine looks like this:

As you can see, this subroutine checks each radio button list to see if the correct item has been selected and for each correct response on the page, it updates an integer variable  called "correct" to contain that list.  After calculating the score, the integer variable is used to update the text used to display the number of correct responses made.

That pretty much covers it, the web page in operation looks like this:

 
Figure 1:  Test Web Site In Operation

Summary.

This article discussed a simple method that may be used to bring sound to a web site through the use of a custom control.  There are other available methods including pure JavaScript methods that will do the same thing.  This approach demonstrates using a post-back event as the basis for loading and playing a new sound, if you need or want to play sounds without the post-back, then you should look to the pure JavaScript approaches.