Kill the session when the browser is closed

In one of my projects, I used Form Authentication to authenticate users against our Intranet domain by using LDAP.  The good things are users don't have to remember another pair of user name and password, and form authentication gives users ability to log out.  Users cannot log out if we use Windows Integrated Authentication.

By design, if users click something which they don't have permission, form authentication will automatically redirect them to the login page, and there users can log in with another account to access the desired resource.  However in some use cases, users don't like this behaviour.  They argue that it's rare that users have 2 accounts in the system.  So if they don't have permission, we don't have to redirect them to the login page.  We just need to display some messages indicating they need an admin to reassign them the proper permission.  Here I just have a workaround when users are redirected to the login page, I will display some information on the login page to explain why they are showed the login page.

Another user requirement is users want to kill the session and log out when the browser is shut down.  This requirement looks simple but It took me a long time to work on it.  Even worse is so far I haven't gotten the proper way to resolve the problem.  But I did get some workarounds in this stage.

When I searched from the internet, most people said you couldn't log out automatically. This is true in that the session is stored in the server, when users close the browser, the browser normally just closes and won't send a message to the server.  So the server never knows the client is already gone.

But when you go to some bank websites, closing browser will log you out immediately.  When you go to the same site again, the site always asks for your credentials.  I don't know how exactly they are doing.  However, I think they might use their own login mechanism.  Users are always directed to the login page when users first open the website.  When login page opens, the website always clear the old session and old credentials, so users have to enter their account again.  Since in the middle, they won't be redirected to the login page, so this clearing won't bring trouble.

I referenced this blog and this discussion and this discussion to implement my workaround.

First created the Exit.aspx page.  In the page load method, do the following:

    protected void Page_Load(object sender, EventArgs e)
    {
        FormsAuthentication.SignOut();
        Session.Abandon();
       
        // clear authentication cookie
        HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName, "");
        cookie.Expires = DateTime.Now.AddYears(-1);
        Response.Cookies.Add(cookie);

        FormsAuthentication.RedirectToLoginPage();
    }
The code kills the session and logs out the user.  I put the code in the page load event handler so this page will never be displayed.

Then in the normal pages add the following javascript code.  Since I have a master page for all my pages, I can put this code in my master page so every page will be affected.

<script type="text/javascript" >
    var closeTab = false;
    window.onbeforeunload = checkBrowserBefore;
    window.onunload = checkBrowserUnload;

    function checkBrowserBefore() {
        if (window.event.clientY <= 0) {
            closeTab = true;
            return "Do you leave the application or stay?";
        }
        else
            closeTab = false;
    }
    function checkBrowserUnload() {
        if (closeTab)
            window.location.href = "../Exit.aspx";
    }
</script>
Notice here I check 2 events onbeforeunload and onunload.  When users close the browser tab or browser, the onbeforeunload will fire.  In IE a message box will pop up asking user to confirm the closing.  If user clicks Yes, or in some new IE versions users choose Leave the page, the onunload will fire.  Otherwise the onunload will not fire.  That's the reason we have to check both events.

Again we should remember this is just a workaround and not guaranteed.  This workaound only works in IE, but not even in all IE versions.  In IE7, it works when users close either the IE tab or the entire IE browser.  But in IE9, it works when users close the IE tab, but not working when users close the  IE browser.  I haven't tested on other IE versions or other browsers.

Also it is not working when users kill the browser process in task manager or use Alt + F4 to close it.

DevTeach 2010 Toronto

DevTeach 2010 Toronto is held in Microsoft headquarter in Mississauga on Mar 8-12.  The main conference is from Mar 9 to Mar 11, plus one day pre conference workshop and one day post conference workshop.  The main conference attendees are eligible for one year MSDN subscription.  That is probably why so many people attended the conference.

Comparing to TechDays, the sessions in DevTeach are more advanced.  These sessions cover architecture, agile, silverlight, sharepoint, and general web and Windows development. I took the main conference and pre conference workshop.  I don't think the pre one deserves the cost ($400 one day).  The Silverlight workshop I took only simply shows a series of sessions which we probably already knew in some previous Techdays sessions.  Plus the organizing is not professional.

I like the main conference.  The presenters impressing me include Michael Stiefel, Kimberly Tripp, Donald Belcham, etc.  Some architecture sessions are very attractive, most of which are related with interface, layer, design pattern, design principle, and ORM.  A couple of SQL sessions from Kimberly Tripp are outstanding.  I also took some sessions which focus on particular fields, such as jQuery, LINQ, SharePoint, and Web farm. 

It's beneficial and important to know what the people in the community are thinking and doing.  When you listen to people, you can refresh your memory and probably come out some new ideas.  I hope this conference experience can help improve our in-house WPF and Silverlight projects.

Silverlight and JavaScript interaction

In Silverlight business applications, we may need to pass data to the Silverlight control.  If the volume of data is not big, we can consider using Silverlight HTML Bridge to communicate between JavaScript and Silverlight. This post summarizes how to call JavaScript from Silverlight and vice versa.

Silverlight HTML Bridge is the technology that enables to call JavaScript from Silverlight managed code and call Silverlight managed code from JavaScript.  The following example will use some simple code to demonstrate the 2 parts and point out some usual difficulties developers may encounter.

Call Silverlight from JavaScript

In the test.aspx file, I have the following form:   

    <form id="form1" runat="server" style="height:100%;">
        <asp:ScriptManager ID="ScriptManager1" runat="server">                          </asp:ScriptManager>
        <div>
            <input type="button" value="Start Silverlight" onclick="startSilverlight();" />
            <input type="hidden" id="hiddenString" value="0.85,0.78,0.10,0.12,0.90" />
        </div>
        <div style="height:100%;">
            <asp:Silverlight ID="Xaml1" Visible="true" runat="server" Source="~/ClientBin/SilverlightTest.xap"                             MinimumVersion="2.0.31005.0" Width="100%" Height="100%" />
        </div>
    </form>

And I also have the following JavaScript in the same page: 

<script type="text/javascript" language="javascript">
    function startSilverlight() {
        var plugin = document.getElementById("Xaml1");
        if (plugin == null) {
            alert("xaml1 is null");
            return;
        }

        var strControl = document.getElementById("hiddenString");
        var str = strControl.value;
        plugin.Content.Page.StartShow(str);
    }
</script>

In Silverlight, the code-behind file contains the following code:

    [ScriptableType]
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();
            HtmlPage.RegisterScriptableObject("Page", this);
        } 

        [ScriptableMember]
        public void StartShow(string data)
        {
            char[] charSeparators = { ',' };
            string[] result;
            result = data.Split(charSeparators, StringSplitOptions.RemoveEmptyEntries);
            float values[] = new float[result.Length];

            int i = 0;
            foreach (var str in result)
            {
                values[i++] = float.Parse(str);
            } 

            UpdateLayout(values);
        }
    }

When users click the button on test.aspx page, the hidden text can be passed to Silverlight.

Call JavaScript from Silverlight

In test.aspx, I added

<script type="text/javascript" language="javascript">
    function getSilverlightValue(text) {
        alert(text);
    }
</script>

In Silverlight code-behind file, use HtmlPage to call the function: 

    HtmlPage.Window.Invoke("getSilverlightValue", "A test string");

Final Words

This is all the things related with how JavaScript and Silverlight interact. However, what I want to point out here is this convenient method may have some performance issues when you want to pass high volume of data to Silverlight.  In my real project, I passed over 30 Mega pure data to Silverlight and I needed to parse the data, so the data needed over 10 seconds to be fully displayed.  Some users may not want this experience.  If that's the case, you may seek help from WCF to retrieve data in an asynchronous way.

Set the DefaultFocus and DefaultButton in a master page

From ASP.NET 2.0 it is possible to set the default focus and default button with the DefaultFocus and DefaultButton properties which HtmlForm has.  DefaultFocus sets which control to get the default focus in a form, and DefaultButton decides which button will fire the click event when users hit the enter key.  In a page which uses a master page, you know the control name will be added a prefix string like ctl00_ContentPlaceHolder1_.

My example form has one EditBox named txtName and one Button named btnView.  If I use the following code in the Page_Load event:

Page.Form.DefaultButton = btnView.ID;
or
Page.Form.DefaultButton = "btnView";

I get the following error:
The DefaultButton of 'form1' must be the ID of a control of type IButtonControl.

The reason is the control name is changed in a master page.  So we have to use the following one in this case:
Page.Form.DefaultButton = btnView.UniqueID;

But for DefaultFocus, UniqueID seems not working for me.  I have to use ClientID instead of UniqueID:
Page.Form.DefaultFocus = txtName.ClientID;

An alternative is use Focus() method.  You could use the following to get the same effect as the above one:
txtName.Focus();

Sometimes you may want 2 or more default buttons on one page.  This can be implemented by putting asp:Panel control around the controls.  In the following example, when the cursor is in TextBox1, Button1 is the default button, otherwise when the cursor is in TextBox2, Button2 is the default button. 

<asp:Panel ID="Panel1" DefaultButton="Button1" runat="server">

    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

</asp:Panel>

<br />

<asp:Panel ID="Panel2" DefaultButton="Button2" runat="server">

    <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>

    <asp:Button ID="Button2" runat="server" Text="Button" onclick="Button2_Click" />

</asp:Panel>

Tech Days Toronto 2009

Tech Days Toronto came again. This year it was held one month early, on Sep. 29 and 30, 2009 at Metro Toronto Convention Centre, Downtown Toronto. It's said there were more people (1200 comparing to 1000 last year) attending the conference. It looks like the recession didn't affect companies' budget. :) I like the time and venue of this year. I didn't have to drive in the highway in the rush hour as last year. The time was one month earlier than last year, and Toronto was still warm.

Again this year all the presenters were from the partners of Microsoft, many of which had direct development and project experience. Several of them also presented in last year's Tech days. The good thing is the overall presentation skills of speakers are better than last year. In all 8 sessions (plus one bonus session) I attended, the speakers all had good presentation skills, and the materials were well prepared.

Let's talk about the sessions. In my opinion, this year is better than last year. Especially I like the added Developer Foundations track, which they said is coming from the feedback of many developers. This track was talking about some topics which could bring the developers to another level. One example was the five OO design principles. Of course we cannot expect too much from just 1 hour and 15 minutes (the total time of a session). The thing is you could get some ideas from other developers, and grasp a chance to practice in your own software development.

Except the Developer Foundations track, I mainly took some sessions for developers on Microsoft-based platform, such as Silverlight 3, Expression Blend for Developers and Prism. What I got from the sessions can be summarized as follows:

1. As Silverlight or WPF developers, we have to use Expression Blend in design time. It's impossible to write complex XAML tags in Visual Studio. Although developers usually don't like the design work, Expression Blend can save you tons of time when you need a complex XAML file, i.e. a multi-dimension animation.
2. Silverlight 3 adds some new features, one of which is mouse wheel event support. Previously I created my own mouse wheel event handler. I need to check if the new features make the development easier.
3. I heard several times about Prism and ASP.NET MVC, but I just don't know if they are practical and effective in real business projects. I will spend some time to investigate these frameworks and see if they can improve my projects.
4. The best practise for developers is to get to know broadly any relative technologies. Some Java techniques could help .NET developers create a good design. Although I had experience in some other fields (except .net and c++) like Java, Mobile development, BI, I need some time to update my knowledge.