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)";
 }
}

 

Calling javascript function from silverlight

Introduction

When working with Silverlight, we are working with managed code (C#, VB). Sometimes, we need to callback to HTML page from managed code.
In this article, we walkthrough how to call managed code from JavaScript and call JavaScript function from managed code.

Background

To call JavaScript function from Silverlight, HtmlPage class of System.Windows.Browser namespace is used to allow the user to access and manipulate browser DOM (Document Object Model).
ScriptableMemberAtrribute class indicates that method or property is accessible for JavaScript caller.
To permit user to access method of Silverlight from JavaScript, you have to set [ScriptableMember] attribute to that method.

Using the Code

Let's start step by step including source to demonstrate how to communication between JavaScript and Silverlight.

First we start with Calling JavaScript function from Silverlight

Step 1: First, create one class in a Silverlight project, which describes method to call from JavaScript.

Step 2: Switch to Web project and open HTML page.

Step 3: Create Method in HTML page called from Silverlight

//.js file

function alertText(text) {

alert(text);

}
function sendText() {

return "Hi from Javascript!";

}

Step 4: In User Control, create Button to call JavaScript function.

//page.xmal

<Grid x:Name="LayoutRoot" Background="Transparent">

<Grid.RowDefinitions>

<RowDefinition Height="50"></RowDefinition>

<RowDefinition Height="50"></RowDefinition>

</Grid.RowDefinitions>

<Grid.ColumnDefinitions>

<ColumnDefinition Width="200"></ColumnDefinition>

<ColumnDefinition Width="200"></ColumnDefinition>

</Grid.ColumnDefinitions>

<Button x:Name="btnFireJavascript" Grid.Column="0" Click="btnFireJavascript_Click" Width="100" Height="30" Content="Send Data!"></Button>

<Button x:Name="btnReceiveJavascript" Click="btnReceiveJavascript_Click" Grid.Column="1" Width="100" Height="30" Content="Receive Data!"></Button>

<TextBox x:Name="txtReturnData" Height="30" Width="150" Grid.Row="1" Grid.ColumnSpan="2"></TextBox>

</Grid>

//page.xaml.cs

private void btnFireJavascript_Click(object sender, RoutedEventArgs e)
{
HtmlPage.Window.Invoke("alertText", new string[] { "Hi!" });
}
private void btnReceiveJavascript_Click(object sender, RoutedEventArgs e)
{
string obj = HtmlPage.Window.Invoke("sendText", null) as string;
txtReturnData.Text = obj;
}

By clicking on button, we need to invoke JavaScript function by using System.Windows.Browser.HtmlPage.Window.Invoke method. This method will call JavaScript "sendText" method will return the entered text disyplay the "alertText" method with "From Silverlight" as alert messagebox.In the next step, write method in HTML page of Web project has XAP file as a Object parameter.
 Step 5: Drag the reference of the js file to Web project

//silverlighttestpage.aspx drag reference

<script type="text/javascript" src="MyFunctions.js" ></script>

This is just a simple demo example, you can also use Silverlight property from JavaScript as well as JavaScript member from Silverlight.

Please put he comments.......