A Windows Form like MessageBox for ASP.NET Website

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Introduction

This small tip discusses about a very small class that provides a Window's form like MessageBox functionality in an ASP.NET application.

Background

I come from a C++/MFC and C#/Winforms background. The developers working with these will definitely agree to the fact that MessageBox is a very useful UI element that can be used to display quick information to the users and also proves very useful in quick debugging. I started working in ASP.NET last year and missed this small fellow a lot. So I decided to have one for me which will use server side code to provide a quick message pop up on the web page using client side scripting.

Using the Code

The class for MessageBox is very simple. It contains a single function Show(). This function is a static function so that we can call this in the same way we do on a Windows form, i.e., MessageBox.Show("Some Message");

The main thing to notice in this class is that it keeps track of the messages coming from all the pages of the website. Also, it shows these messages when the Page_Unload is getting called after the postback. The reason for doing that is that the user should be able to see the web page in the background when the message comes on screen (which will not be the case if we don't put it in Unload event). Here is the class for MessageBox.

public class MessageBox
{
    // Lets keep the message coming from all the pages here
    static Dictionary<Page, Queue> pageTable = null;    

    static MessageBox()
    {
        // Create the store
        pageTable = new Dictionary<Page, Queue>();
    }

    public static void Show(string str)
    {
        // Lets find out what page is sending the request
        Page page = HttpContext.Current.Handler as Page;

        // If a valid page is found
        if (page != null)
        {
            // Check if this page is requesting message show for the first time
            if (pageTable.ContainsKey(page) == false)
            {
                // Lets create a message queue dedicated for this page.
                pageTable.Add(page, new Queue());
            }

            // Let us add messages of this to the queue now
            pageTable[page].Enqueue(str);

            // Now let put a hook on the page unload where we will show our message
            page.Unload += new EventHandler(page_Unload);
        }        
    }

    static void page_Unload(object sender, EventArgs e)
    {
        // Lets find out which page is getting unloaded
        Page page = sender as Page;

        // If a valid page is found
        if (page != null)
        {
            // Extract the messages for this page and push them to client side
            HttpContext.Current.Response.Write
            	("<script>alert('" + pageTable[page].Dequeue() + "');</script>");
        }
    }
}

And with this class in place, we can simply call the function as:

MessageBox.Show("Hello World 1");

Which would result in a message box on screen like:

Points of Interest

After completing this small exercise, I am thinking of extending this class to support all the overloaded versions of the MessageBox.Show() function. Once I do that, I will perhaps update this small tip.

History

• 20^th April, 2012: First version