Slide Show In asp.net

I had been looking for the source of a web-based slide show. The features I wanted in my slide show pages were that it should dynamically select a picture in the server to display, it should display some transition effects, and it should not cause page refreshing. But I couldn’t find one of this kind. So I decided to code it myself.There is a lot of source code to make the transition effect using JavaScript. But to address the dynamic selection of the picture to display and to avoid the page from refreshing, I used AJAX. There are a lot of AJAX frameworks and tools out there to choose from. But for this simple task, I just used the ASP.NET2’s built-in AJAX supported class system.Web.UI.ICallbackEventHandler.

The included source code will demonstrate the use of this class, and also how to use JavaScript to make the request to get the next image file and apply the transition effects. One thing I need to mention is when applying transition effects, the next image has to be completely loaded before playing the effect, otherwise, the picture display will not be smooth and will be flickering. I also address this in my JavaScript code.


//.aspx page
<img id="photo" src="" runat="server" border="0" style="height: 150px; width: 400px;" />

//javascript function
<script type="text/javascript">
 //A timer will be fired in 5 seconds to call getNextImage()
 var c_interval = 5000;
window.setTimeout("getNextImage()", c_interval);
function getNextImage() {
 //Send the request to server with the current image url as the argument
CallServer(document.getElementById("photo").src, "")
}
function ReceiveServerData(rValue) {
 //Receive server's response of a string rValue, which is prepared in the server's function
//GetCallbackResult()
 var wds = rValue.split(";");
 //Assign the transition effect
 document.getElementById("photo").style.filter = wds[1];
 //Preload the image file from server. When finishing download, imageLoaded function will be called
 //with the img object as the argument
 var img = new Image();
 img.onload = function () { imageLoaded(this); }
img.onerror = function () { imageError(this); }
 img.onabort = function () { imageError(this); }
 img.src = wds[0];
}
function imageError(img) {
 //If image download errors occur, this function will be called.
 window.setTimeout("getNextImage()", 1000);
}
function imageLoaded(img) {
var photo = document.getElementById("photo"); //Find the image control object
photo.filters[0].apply(); //Apply the transition effect
photo.filters[0].play(); //Play the effect and display the new image
photo.src = img.src; //Assign the image to the image control
window.setTimeout("getNextImage()", c_interval); //Initiate the next request
 }
</script>


//.cs file
string m_lastFileName = "none";
protected void Page_Load(object sender, EventArgs e)
 {if (IsPostBack)
     return;
  photo.Src = GetNextImageUrl();
//Register Ajax client script to client's browsers. This has to be hard coded.
 string cbReference = Page.ClientScript.GetCallbackEventReference(this, "arg", "ReceiveServerData", "context");
 string callbackScript = "function CallServer(arg, context)" + "{ " + cbReference + "} ;";
 Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "CallServer", callbackScript, true);
}
public void RaiseCallbackEvent(string eventArgument)
 {
//This is first place to receive the callback from client's browser. The parameter 'eventArgument'
 //is the parameter passed from the Javascript's call 'CallServer()'. In this example, it is the
 //last image url.
 m_lastFileName = Path.GetFileName(eventArgument);
 }
public string GetCallbackResult()
{
//This is the second call triggled by the 'CallServer()' and it is the place to prepare and return a string
 //to the client. Here the returned string is the image url and the transition effect.
 return GetNextImageUrl() + ";" + GetNextTransition();
 }
private string GetNextImageUrl()
 {
//Randomly pick a image file in the server.
 string[] files = Directory.GetFiles(AppDomain.CurrentDomain.BaseDirectory + "Images", "*.jpg");
if (files.Length == 0)
    return string.Empty;
while (true)
 {
int n = (int)((files.Length - 1) * (new Random()).NextDouble());
 //Do not want to repeat the last image
 if (files[n].IndexOf(m_lastFileName) < 0)
 {
return files[n].Replace(AppDomain.CurrentDomain.BaseDirectory, string.Empty);
 }
}
}
private string GetNextTransition()
 {
//Randomly pick a transition effect. Note some of the effects only work in IE.
 int n = (int)((new Random().NextDouble()) * 5);
 switch (n)
 {
case 0:
 case 1:
 n = (int)((new Random().NextDouble()) * 22);
 return "revealTrans(duration=2,transition=" + n.ToString() + ")";
 case 2:
 case 3:
 if (Request.Browser.Browser == "IE")
{
n = (int)((new Random().NextDouble()) * 8);
 switch (n)
 {
case 0:
 return "progid:DXImageTransform.Microsoft.RandomDissolve()";
 case 1:
 return "progid:DXImageTransform.Microsoft.Pixelate(MaxSquare=20, Duration=2, Enabled=false)";
 case 2:
 return "progid:DXImageTransform.Microsoft.RadialWipe(wipeStyle='clock')";
 case 3:
 return "progid:DXImageTransform.Microsoft.Wheel(spokes=4)";
 case 4:
return "progid:DXImageTransform.Microsoft.Stretch(stretchStyle='spin')";
 default:
 return "progid:DXImageTransform.Microsoft.Stretch(stretchStyle='push')";
 }
}
else
 return "blendTrans(duration=2)";
 default:
 return "blendTrans(duration=2)";
 }
}