Coding with .NET

Last Day of MIX11

2011-04-14T10:54:00.001-05:00

Well the slots have been evil but the tables have been kind. MIX11 is drawing to a close. There’s a full day of sessions ahead of me, immediately followed by a flight where I lose 2 hours due to the time change, immediately followed by a 3 hour drive back to Shreveport. Good food, good swag, and good information. Looking forward to next year…

For now, I’m off to check out Mads Kristensen’s talk on Bigger, Faster, Stronger: Optimizing ASP.NET Applications. If that name sounds familiar then maybe you’ve used BlogEngine.NET. Mads is the founder.

Haack on MVC3

2011-04-14T09:13:00.001-05:00

Phil Haack is giving a talk on what’s new with MVC3. Even though it’s been out for a while now, I’m sure there are still plenty of developers who haven’t tried it yet. MVC3 was my first experience with MVC. I skipped MVC1 and MVC2 while trudging along with web forms and finally decided last December that it was time to make the jump. A very wise decision, to say the least, and I haven’t looked back.

The first thing to note is the release of the ASP.NET MVC3 Tools Update. One of the things this introduces is a new project template for intranet applications. The main difference with this is that it uses NTFS authentication instead of introducing an account controller. There is also a new option to use HTML5 semantic markup which will include Modernizr with your views. There are other new features available with this update and you can learn more about it over on Phil’s blog.

Scaffolding

2011-04-13T18:43:00.001-05:00

Steven Sanderson, Program Manager, is giving this talk on ASP.NET, NuGet, Entity Framework Code First, and more. I’ve used CodeSmith in the past so we’ll see if this session will offer anything that could replace its usage.

…

Wow! That was a whirlwind. I don’t even know where to start. For this one I’ll defer to a very detailed explanation that covers most of what went on in this session.

Building Data-centric N-tier Applications with jQuery

2011-04-13T17:02:00.001-05:00

Brad Olenick is giving this talk and from the description he should go into using WCF with jQuery, something I haven’t tried yet. Here we go…

RIA/JS is a jQuery client for WCF/RIA services and is available today via NuGet.

The demo looked interesting but it seems like there’s a lot of voodoo going on under the hood, which we didn’t get to see. I’ll be downloading the plug-in to explore what’s underneath it, if for nothing else.

Hacking with the F12 Developer Tools

2011-04-13T16:25:00.001-05:00

I spend a lot of my day in these dev tools so I’m hoping to learn some new tips and tricks to make my day a little easier. Martin Beeby is presenting this session. Here we go…

Well I learned one new thing, you can format JavaScript in the tools which is especially useful if you’re dealing with a minified version of that js file. Turns out you can also use your up and down arrow keys to increment or decrement integer values like height and width.

The profiler and network tabs are nice additions to the tools and features I haven’t dealt much with yet. The network tab gives you something similar to what Fiddler would.

One of the tools I use on a regular basis is the Screen Calipers from Iconico. The dev tools now include a ruler similar to (but not as slick as) the Screen Calipers. There is also a color picker which, again, isn’t quite as slick as the tool I normally use, ColorPic, but is functional nonetheless.

Good talk but quick.

Going Mobile with Your Site on IE9 and Windows Phone 7

2011-04-13T14:18:00.001-05:00

With IE9 coming to Windows Phone 7 soon the gap between native apps and mobile websites will be that much smaller. Joe Marini, Principal Program Manager for Internet Explorer on Windows Phone is giving this talk to explore the new capabilities coming this fall to Windows Phone 7 with the Mango update.

Time passes…

For the most part this talk mostly covered a common sense approach to web development regarding targeting mobile browsers. Most of the things discussed were to be expected: optimize images, use feature detection over browser-sniffing, don’t include gratuitous use of background imagery or fancy fonts, etc.

Lots of good things coming with Mango, including geolocation (with GPS), HTML5 audio/video capabilities, and CSS media queries.

MIX11 Day 2 Keynote

2011-04-13T11:01:00.001-05:00

Day 2 here at Mandalay Bay and everyone is gearing up for today’s keynote with The Gu and Joe Belfiore. Let’s see what kind of Windows Phone 7 announcements they have for us…

8:55 am

DJ Z-Trip is serenading us with some Led Zeppelin and Public Enemy, good stuff.

9:05 am

Joe Belfiore takes the stage to kick things off…

9:10 am

Joe is addressing the Windows Phone 7 update issues.

9:15 am

Joe is going through some of the new things coming with the Mango update coming this fall, including additional language and country support.

9:20 am

Live demo with a recent build of Mango… The app jump list now has the same capabilities as contacts with search and alphabet shortcuts. Podcast support from the marketplace will be available as well. Similar to the feature currently available in the hubs, users will be able to, for example, do a web search for movies then select a “card” which could show additional information about the search as well as allowing the user to slide over to additional screens like “extras.”

9:30 am

Joe is now going over the biggest feature I’ve been waiting for… IE9 will be the native browser with the fall Mango release. Joe is currently demonstrating some HTML5 video and audio capabilities including playing background audio from the browser while using other apps on the phone.

9:35 am

Joe is now demonstrating the hardware acceleration capabilities blowing iPhone and Android away.

9:40 am

Ringtones! Access to sensors, including the camera, compass, gyroscopes, etc.

9:43 am

Motion Sensor was just announced which will make it easier to work with the compass and gyroscope.

9:45 am

Multi-tasking – fast app switching, background audio, background downloads, alarms, etc.

9:47 am

May 25th – Angry Birds!

9:50 am

Demo now of Live Agents which is background app/task management balancing background functionality with battery usage.

9:52 am

The new phone tools will be available in May.

9:55 am

Scott Guthrie has just taken the stage. Right into a demo… The new tools will have an accelerometer available within the emulator and it looks great. They’ll also include location options for the emulator to test location-based apps.

10 am

Scott is now demonstrating some of the new debugging features that will be available including performance logging and analysis. The amount of detail available is insane. You can drill down to a specific frame if need be.

10:05 am

Lots of performance improvements coming with Mango that will require no code changes. Also, Mango will include around 1500 new APIs.

10:10 am

Local SQL with LINQ support! Demo… Network sockets will be available as well. Demo…

10:15 am

Mike Roberts is now demo-ing Kik Messenger, a chat app which will be available in a few weeks.

10:20 am

Camera capabilities… Ben Riga is demo-ing some new ways to interact with the camera on the device.

10:25 am

Silverlight and XNA will be able to exist in the same app.

10:30 am

Silverlight for the browser… Silverlight 5 contains hundreds of new APIs. Hardware-based video decode will be available. Silverlight will also take advantage of IE9’s hardware acceleration. Remote control input will be available as well.

10:35 am

Blue Angels' website demo.

10:40 am

Silverlight 5 new features demo with John Papa… 2D to 3D projection looks nice.

10:43 am

Silverlight 5 Beta and tools support is now available for download. RTM will be available later this year.

10:45 am

Kinect – Kinect for Windows SDK will be available later this spring! Demos…. I want that chair yo!

10:55 am

Worldwide telescope – wow!

11 am

We all get Kinects! Sweet!

All in all today’s keynote was much better than yesterday’s, lot’s of good info. I’m looking forward to working with some of the new phone tools.

On to the sessions…

Making Better Web Apps for Today’s Browsers

2011-04-12T17:26:00.001-05:00

Making Better Web Apps for Today’s Browsers is the talk I’ve been looking forward to most today. I’m hoping it will continue along the same lines as what was discussed in 50 Performance Tricks to Make Your HTML5 Web Sites Faster.

HTML5 To The Rescue

2011-04-12T16:04:00.001-05:00

I’ve been looking forward to this one, 50 Performance Tricks to Make Your HTML5 Web Sites Faster. Jason Weber gave a similar talk last year that went into a lot of detail about the little things a developer can do to keep his sites performing at their best.

Battery died during the session, but there were lots of good tips. Some were recaps from last year such as using image sprites and always linking CSS files at the top of the page but a lot of them were new this year like how to properly leverage SVG and some of the new capabilities of HTML5. Good talk all around.

Orchard!

2011-04-12T13:34:00.001-05:00

The keynote was kind of meh but now I’m in Deconstructing Orchard: Build, Customize, Extend, Ship. I’ve had bad experiences with CMS’s in the past but Bradley Millington convinced me at Open Source Fest that Orchard was worth taking a look at so here we go…

…time passes…

So far it doesn’t look bad at all. Lots of customization features with modules and plenty of common problems already solved within the gallery. Lots of hooks for extensibility…

The shape tracing feature is really slick. Sort of like firebug just for Orchard. You can trace through the UI and ultimately create and edit a file to override the default file for the section you’re interested in. Apparently there is also some form of theme inheritance to allow customization to fall back through several levels.

Good stuff, I’ll definitely be checking it out.

MIX11 Day 1 Keynote

2011-04-12T11:15:00.001-05:00

9:05 am

Dean Hachamovitch just took the stage wearing a shirt that says “ten” with the IE logo as the e… hmm…

9:20 am

xtranormal is the shizzle…

9:30 am

IE10 Demo!

9:35 am

Looks like they’ve added support for CSS columns, transitions, and gradients among other things.

9:40 am

Dean just announced that the IE10 Platform Preview 1 is available for download today.

9:45 am

Scott Guthrie just took the stage… The MVC tools have been updated and Entity Framework 4.1 is live!

9:50 am

Scott Hanselman just took the stage…

9:55 am

Scott is going through an EF code first demo and also demonstrating some of the new MVC tooling.

10 am

WebMatrix demo going on now… not a fan from what I’ve seen and heard in the past. Not a fan from what I’m seeing now either. Why do we need yet another way to make websites?

10:10 am

Sweet, Orchard demo! Bind Tuning looks pretty slick for customization. There are some nice e-commerce plug-ins available as well.

10:25 am

Windows Azure time… with an Umbraco presentation. The admin section has options to automatically scale based on traffic using the windows azure APIs.

10:30 am

Scott Guthrie announced several new services for Windows Azure including, access control service, caching, content delivery network, and traffic manager.

10:35 am

Looks like the keynote is wrapped up… off to some sessions.

MIX 2011–Here we go

2011-04-12T11:05:00.001-05:00

Mix11! I had a great time last year so I have high expectations for this year. The event was kicked off with Open Source Fest (above) and there was a great turnout as you can see. Surprisingly, the Orchard Project held most of my attention. I’ll definitely have to check into that further.

Currently everyone is waiting for the Day 1 keynote to begin. More soon…

MIX Day Three

2010-03-17T11:29:00.001-05:00

Here we are on the final day of MIX. Thanks to Microsoft for putting on a great party last night at LAX in the Luxor. Also, thanks to Scott Hanselman and the guys at Bing for hosting Nerd Drinks at Wynn Encore earlier in the evening.

No keynote today, only sessions, and plenty of them. I’m starting off with Building Platforms and Applications for the Real-Time Web then on to Building Large-Scale, Data-Centric Applications with Silverlight, Participating in the Web of Data with Open Standards, Peanut Butter and Jelly: Putting ‘Content Management’ Back into CMS, and Building a Next-Generation Web Application with Microsoft ASP.NET MVC 2 and jQuery. Needless to say, it’s going to be a long day with plenty of information to absorb.

All in all, I’ve had a great time. I’ve learned a lot, got some swag, and met some good people. Over the last few days I’ve shared conversations with developers across a wide array of technologies and from various parts of the world. Sitting at my table last night at LAX there were developers from all over the United States as well as Iceland and Sweden. The sessions are great but the networking opportunities add a great deal to MIX as well.

I’ve followed MIX every year since inception but this is the first time I’ve been able to check it out live. If you haven’t been, it’s definitely worth the time and money to come out next year. Now, I should probably get back to my sessions…

MIX Day Two Keynote Announcements

2010-03-16T10:17:00.001-05:00

Update (11:10am):

Interesting talk from Bill Buxton about the concept of Natural User Interface to wrap up the keynote. Looking forward to today’s sessions.

Update (10:30am):

Project codename “Houston” announced to manage SQL Azure databases directly in the browser. Also, SQL Azure databases are now able to expose data automatically by simply clicking a checkbox to enable OData.

Update (10:25am):

Lots of news around OData… Check out all of the details at http://www.odata.org/.

Update (10:10am):

Netflix has made an oData API available at http://odata.netflix.com/Catalog/

Update (9:55am):

Microsoft is contributing to jQuery development.

Update (9:35am):

HTML5 Video! HD, opacity, hardware acceleration.

Update (9:30am):

Dean Hachamovitch just announced the IE9 Platform Preview and went through some amazing demos that left other browsers in the dust. HTML5, SVG, GPU leverage…

Update (8:50am):

Minutes away…

8:15am:

Day one for MIX is over and now everyone is gearing up for today’s keynote. IE9 is sure to be a hot topic with the biggest question being, “When do we get a beta?” I’ll be updating this post with the answer to that question, along with any other major announcements, throughout the keynote.

Lots of great sessions today… personally I’m checking out What’s New in Microsoft ASP.NET MVC 2, Building Facebook Apps with Microsoft .NET and Deploying to Windows Azure, and either The Elephant in the Room or High-Performance Best Practices for Web Sites. There are several others I’d like to see as well, but I guess I’ll have to check those out after the fact on the MIX site.

Don’t forget, even if you’re not here you can watch the MIX Day Two Keynote live.

MIX Day One Keynote Announcements

2010-03-15T10:46:00.001-05:00

Update (11:10):

MIX Day One Keynote has just wrapped up. Windows Phone Developer Tools are now available for download! Great demos and lots of code made available today. Looking forward to the sessions this afternoon.

Update (10:25am):

Scott Guthrie just announced that all of the Windows Phone 7 development tools will be free.

Update (10:10am):

Scott Guthrie just showed the Windows Phone 7 development experience within VS 2010 and the emulator is as smooth as can be. Multi-touch support is also available if you’re using a multi-touch Windows 7 system.

Update (10:00am):

Joe Belfiore just got done showing some sweet demos with Silverlight and XNA. Very intuitive, great design.

Update (9:35am):

Silverlight 4 RC is now available for download.

Update (9:20am):

Scott Guthrie just announced free upgrade to Expression Blend 4 for all Expression Blend 3 users.

Update (9:15am):

Scott Guthrie just announced that a ton of Silverlight code (editing, playback, etc.) will be open sourced. Also, with Silverlight 4, users will be able to stream HD video full screen on one monitor while continuing to work on other monitors.

Update (9:10am):

MIX has begun!

Update (9:05am):

You can’t play with my yo-yo!

Update (8:45am):

MIX is about to begin

2010-03-15T10:20:00.001-05:00

Good morning! We’re 45 minutes away from the day 1 keynote and everyone is full of speculation regarding what announcements are forthcoming. Follow MIX with a live stream available at http://live.visitmix.com/.

Viva Las Vegas!

2010-03-14T19:04:00.001-05:00

Well I made it to Vegas safe and sound. I have a ton of sessions lined up over the next few days. I’m particularly looking forward to Building Offline Web Apps Using Microsoft Sync Framework, What's New in Microsoft ASP.NET MVC 2, Building Facebook Apps with Microsoft .NET and Deploying to Windows Azure, and Modern Web Form Design. Of course I’m also curious about the surprises that are in store for Windows Phone 7 Series. Could there be some hardware looming? Hmm…

First things first, though, time to go check out the MIX area, mingle for a bit, then find a good burger. Stay tuned.

Heading to MIX 10

2010-03-14T10:36:00.001-05:00

Getting ready to head to the airport so I can hop a plane to Las Vegas. I’ll be updating this blog regularly throughout the week. Looking forward to the new mobile stuff, I wonder what’s in store…

ViewState-backed Properties - Part Two

2008-02-02T15:44:00.001-06:00

Setting a Default Value on the "Get"

This is part two of a multi-part series on using ViewState to back your Page Properties. For those of you who read ViewState-backed Properties - Part One, you'll notice the code is pretty similar. The main difference is that instead of just returning a default value if one hasn't been set, we'll be setting one inside the "Get" portion of our Property. Once again we'll be using one of my favorite operators, the Null Coalescing Operator.

Consider the following code...

private string MyDefaultValue {    get { return (string)(ViewState["MyDefaultValue "] ?? (ViewState["MyDefaultValue"] = "My default value")); }    set { ViewState["MyDefaultValue "] = value; }}

Assuming nothing has been set in ViewState, the right side of the "??" will be evaluated. By wrapping the right side in parenthesis we're telling .NET to evaluate this expression first and then return what's been set. The effect is that not only is our default value returned but it is also persisted in ViewState.

Working Example

Below I've included a working page where we access ViewState directly and through our ViewState-backed Property. More to come in this series.... stay tuned.

<%@ Page Language="C#" AutoEventWireup="false" CodeFile="DefaultAssignment.aspx.cs" Inherits="DefaultAssignment" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >    <head runat="server">        <title>Default Value</title>    </head>    <body>        <form id="frmMain" runat="server">            <div>                <p>                    When this button is clicked, ViewState will be accessed directly (ViewState["MyDefaultValue"]) and nothing will be displayed because it has not been set.                </p>                <asp:Label ID="lblDefaultValue" runat="server" Text="The value is:  " />                <br />                <asp:Button ID="btnDefaultValue" runat="server" Text="Load Default" OnClick="btnDefaultValue_Click" />            </div>            <div>                <p>                    When this button is clicked, instead of accessing ViewState directly we will access the ViewState-backed property causing it to be set and displayed.                </p>                <asp:Label ID="lblSetValue" runat="server" Text="The value is:  " />                <br />                <asp:Button ID="btnSetValue" runat="server" Text="Set Value" OnClick="btnSetValue_Click" />            </div>            <p>                Clicking the first button again will now display the new set value as well even though we never used the "set" of the property.            </p>        </form>    </body></html>

using System;using System.Data;using System.Configuration;using System.Collections;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls; public partial class DefaultAssignment : System.Web.UI.Page{    public DefaultAssignment() { Load += new EventHandler(Page_Load); }     protected void Page_Load(object sender, EventArgs e) { }     protected void btnDefaultValue_Click(object sender, EventArgs e)    {        lblDefaultValue.Text = "The value is:  " + ViewState["MyDefaultValue"];    }     protected void btnSetValue_Click(object sender, EventArgs e)    {        lblSetValue.Text = "The value is:  " + MyDefaultValue ;    }     private string MyDefaultValue     {        get { return (string)(ViewState["MyDefaultValue "] ?? (ViewState["MyDefaultValue"] = "My default value")); }        set { ViewState["MyDefaultValue "] = value; }    }}

ViewState-backed Properties - Part One

2008-01-15T19:50:00.001-06:00

Why use a ViewState-backed Property?

This is the first post in a multi-part series on using ViewState to back your Page Properties. If you've done any kind of development with ASP.NET then you've probably had to use a ViewState-backed Property at some point. Accessing and setting a Property is much easier than working with ViewState directly throughout your code, especially if the name of your Key may change. There is one thing to consider, though.

Default Value for a ViewState-backed Property

It's generally good practice to check your ViewState-backed Property for null before trying to access it. One thing worth noting is that you may want to display a default value if one hasn't been set. The following code may look familiar:

        1: private string Standard

       2: {

       3:     get

       4:     {

       5:         if (ViewState["Standard"] != null)

       6:         {

       7:             return (string)ViewState["Standard"];

       8:         }

       9:         else

      10:         {

      11:             return "My default value";

      12:         }

      13:     }

      14:     set { ViewState["Standard"] = value; }

      15: }

Null Coalescing Operator

Lately there have been quite a few blog posts on using the null coalescing operator (??). I won't go into detail here about its use except to say that it returns the first operand if it is not null and the second operand if the first is null. When applied to ViewState-backed Properties the code can be shortened and, in my opinion, made more readable. Consider the following code which essentially works the same as the previous example:

       1: private string MyDefaultValue 

       2: {

       3:     get { return (string)(ViewState["MyDefaultValue "] ?? "My default value"); }

       4:     set { ViewState["MyDefaultValue "] = value; }

       5: }

If ViewState["MyDefaultValue"] is null then the string "My default value" is returned. If it is not null then the value it holds is cast to a string and returned. In the past, developers have argued that the null coalescing operator makes code more difficult to read. With all the attention it's gotten lately, I no longer think that's a valid argument. In fact, I'll be using it throughout this series on ViewState-backed Properties.

Working Example

Below I've included a working page demonstrating what will be returned before and after the ViewState-backed Property is set. Enjoy!

       1: <%@ Page Language="C#" AutoEventWireup="false" CodeFile="DefaultValue.aspx.cs" Inherits="DefaultValue" %>

       2: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

       3:  

       4: <html xmlns="http://www.w3.org/1999/xhtml" >

       5:     <head runat="server">

       6:         <title>Default Value</title>

       7:     </head>

       8:     <body>

       9:         <form id="frmMain" runat="server">

            <div>

                <p>

                    When this button is clicked, a default value will be displayed even though the ViewState-backed property has not been set.

                </p>

                <asp:Label ID="lblDefaultValue" runat="server" Text="The value is:  " />

                <br />

                <asp:Button ID="btnDefaultValue" runat="server" Text="Load Default" OnClick="btnDefaultValue_Click" />

            </div>

            <div>

                <p>

                    When this button is clicked, the ViewState-backed property will be set and then displayed.

                </p>

                <asp:Label ID="lblSetValue" runat="server" Text="The value is:  " />

                <br />

                <asp:Button ID="btnSetValue" runat="server" Text="Set Value" OnClick="btnSetValue_Click" />

            </div>

            <p>

                Clicking the first button again will now display the new set value as well.

            </p>

        </form>

    </body>

</html>

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

  

public partial class DefaultValue : System.Web.UI.Page

{

    public DefaultValue() { Load += new EventHandler(Page_Load); }

  

    protected void Page_Load(object sender, EventArgs e) { }

  

    protected void btnDefaultValue_Click(object sender, EventArgs e)

    {

        lblDefaultValue.Text = "The value is:  " + MyDefaultValue;

    }

  

    protected void btnSetValue_Click(object sender, EventArgs e)

    {

        MyDefaultValue = "My set value";

        lblSetValue.Text = "The value is:  " + MyDefaultValue ;

    }

  

    private string MyDefaultValue 

    {

        get { return (string)(ViewState["MyDefaultValue "] ?? "My default value"); }

        set { ViewState["MyDefaultValue "] = value; }

    }

  

    private string Standard

    {

        get

        {

            if (ViewState["Standard"] != null)

            {

                return (string)ViewState["Standard"];

            }

            else

            {

                return "My default value";

            }

        }

        set { ViewState["Standard"] = value; }

    }

}

Using the PreviousPage Property with Multiple Previous Pages

2008-01-06T19:56:00.001-06:00

Scenario

Many of you may be familiar with the PreviousPage property of the Page object. It returns the Page object that transferred control to the current page. You may also be familiar with the PreviousPageType directive which provides a way to get strong typing against the previous page.

        1: <%@ PreviousPageType VirtualPath="~/YourSourcePage.aspx" %>
  

In most cases you need nothing more on the target page... unless the target page has multiple previous pages from which it will be expecting data.

Solution

Enter the Reference directive. Only one PreviousPageType directive can exist per page but any number of Reference directives can be used. Most people have used this directive to reference user controls with the following syntax:

       1: <%@ Reference Control="YourControl.ascx" %>
  

The reference directive also has Page and virtualPath attributes, either of which can be used to reference other pages as follows:

       1: <%@ Reference Page="~/YourSourcePage.aspx" %>
  

There is, however, a down side to using the Reference directive over the PreviousPageType directive. The PreviousPage property will have to be cast to the actual previous page type before use. For example, if your previous page's class name was SourcePage and it had a property called Message, it would have to be accessed as follows:

       1: string message = ((SourcePage)PreviousPage).Message;
  

This also means that you'll have to do a check before you can cast it to the correct page like so:

       1: string message = string.Empty;

       2: if (PreviousPage is FirstSourcePage)

       3: {

       4:     message = ((FirstSourcePage)PreviousPage).Message;

       5: }

       6: else if (PreviousPage is SecondSourcePage)

       7: {

       8:     message = ((SecondSourcePage)PreviousPage).Message;

       9: }

      10: else

      11: {

      12:     message = "The previous page is unknown.";

      13: }

Personally I think this is a small price to pay if you only have a few possible previous pages. Otherwise, there are always other options - query string, form collection, session state, etc.

Working Example

For those interested in quickly trying this out, I've included all the code you need below. One scenario has a single source and single target page. The other has multiple sources pointing to the same target page.

Code behind for the single source page used with the single target page:

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

      10: using System.Web.UI.HtmlControls;

      11:  

      12: public partial class SingleSourcePage : System.Web.UI.Page

      13: {

      14:     protected void Page_Load(object sender, EventArgs e) { }

      15:  

      16:     public string Message

      17:     {

      18:         get { return "This is a message from SingleSourcePage.aspx"; }

      19:     }

      20: }

Markup for the single source page used with the single target page:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="SingleSourcePage.aspx.cs" Inherits="SingleSourcePage" %>

       2: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

       3: <html xmlns="http://www.w3.org/1999/xhtml" >

       4:     <head runat="server">

       5:         <title>Single Source Page</title>

       6:     </head>

       7:     <body>

       8:         <form id="form1" runat="server">

       9:             <h1>SingleSourcePage.aspx</h1>

            <div>

                <ul>

                    <li>

                        <a href="SingleSourcePage.aspx">SingleSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageSingleSource.aspx">TargetPageSingleSource.aspx</a>

                    </li>

                    <li>

                        <a href="FirstSourcePage.aspx">FirstSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="SecondSourcePage.aspx">SecondSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageMultipleSources.aspx">TargetPageMultipleSources.aspx</a>

                    </li>

                </ul>

            </div>

            <div>

                <asp:Button ID="btnPostToTargetPage" runat="server" Text="Post to TargetPageSingleSource.aspx" PostBackUrl="~/TargetPageSingleSource.aspx" />

            </div>

        </form>

    </body>

</html>

Code behind for the target page with one previous page:

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

      10: using System.Web.UI.HtmlControls;

      11:  

      12: public partial class TargetPageSingleSource : System.Web.UI.Page

      13: {

      14:     protected void Page_Load(object sender, EventArgs e)

      15:     {

      16:         if (PreviousPage != null)

      17:         {

      18:             lblMessage.Text = PreviousPage.Message;

      19:         }

      20:         else

      21:         {

      22:             lblMessage.Text = "No previous page was detected.";

      23:         }

      24:     }

      25: }

Markup for the target page with one previous page:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="TargetPageSingleSource.aspx.cs" Inherits="TargetPageSingleSource" %>

       2: <%@ PreviousPageType VirtualPath="~/SingleSourcePage.aspx" %>

       3: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

       4: <html xmlns="http://www.w3.org/1999/xhtml">

       5:     <head runat="server">

       6:         <title>Target Page from a Single Source</title>

       7:     </head>

       8:     <body>

       9:         <form id="frmMain" runat="server">

            <h1>TargetPageSingleSource.aspx</h1>

            <div>

                <ul>

                    <li>

                        <a href="SingleSourcePage.aspx">SingleSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageSingleSource.aspx">TargetPageSingleSource.aspx</a>

                    </li>

                    <li>

                        <a href="FirstSourcePage.aspx">FirstSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="SecondSourcePage.aspx">SecondSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageMultipleSources.aspx">TargetPageMultipleSources.aspx</a>

                    </li>

                </ul>

            </div>

            <div>

                <asp:Label ID="lblMessage" runat="server" />

            </div>

        </form>

    </body>

</html>

Code behind for source page one of two for use with the target page accepting multiple previous pages:

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

      10: using System.Web.UI.HtmlControls;

      11:  

      12: public partial class FirstSourcePage : System.Web.UI.Page

      13: {

      14:     protected void Page_Load(object sender, EventArgs e) { }

      15:  

      16:     public string Message

      17:     {

      18:         get { return "This is a message from FirstSourcePage.aspx"; }

      19:     }

      20: }

Markup for source page one of two for use with the target page accepting multiple previous pages:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="FirstSourcePage.aspx.cs" Inherits="FirstSourcePage" %>

       2: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

       3: <html xmlns="http://www.w3.org/1999/xhtml">

       4:     <head runat="server">

       5:         <title>First Source Page</title>

       6:     </head>

       7:     <body>

       8:         <form id="frmMain" runat="server">

       9:             <h1>FirstSourcePage.aspx</h1>

            <div>

                <ul>

                    <li>

                        <a href="SingleSourcePage.aspx">SingleSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageSingleSource.aspx">TargetPageSingleSource.aspx</a>

                    </li>

                    <li>

                        <a href="FirstSourcePage.aspx">FirstSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="SecondSourcePage.aspx">SecondSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageMultipleSources.aspx">TargetPageMultipleSources.aspx</a>

                    </li>

                </ul>

            </div>

            <div>

                <asp:Button ID="btnPostToTargetPage" runat="server" Text="Post to TargetPageMultipleSources.aspx" PostBackUrl="~/TargetPageMultipleSources.aspx" />

            </div>

        </form>

    </body>

</html>

Code behind for source page two of two for use with the target page accepting multiple previous pages:

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

      10: using System.Web.UI.HtmlControls;

      11:  

      12: public partial class SecondSourcePage : System.Web.UI.Page

      13: {

      14:     protected void Page_Load(object sender, EventArgs e) { }

      15:  

      16:     public string Message

      17:     {

      18:         get { return "This is a message from SecondSourcePage.aspx"; }

      19:     }

      20: }

Markup for source page two of two for use with the target page accepting multiple previous pages:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="SecondSourcePage.aspx.cs" Inherits="SecondSourcePage" %>

       2: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

       3: <html xmlns="http://www.w3.org/1999/xhtml" >

       4:     <head runat="server">

       5:         <title>Second Source Page</title>

       6:     </head>

       7:     <body>

       8:         <form id="frmMain" runat="server">

       9:             <h1>SecondSourcePage.aspx</h1>

            <div>

                <ul>

                    <li>

                        <a href="SingleSourcePage.aspx">SingleSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageSingleSource.aspx">TargetPageSingleSource.aspx</a>

                    </li>

                    <li>

                        <a href="FirstSourcePage.aspx">FirstSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="SecondSourcePage.aspx">SecondSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageMultipleSources.aspx">TargetPageMultipleSources.aspx</a>

                    </li>

                </ul>

            </div>

            <div>

                <asp:Button ID="btnPostToTargetPage" runat="server" Text="Post to TargetPageMultipleSources.aspx" PostBackUrl="~/TargetPageMultipleSources.aspx" />

            </div>

        </form>

    </body>

</html>

Code behind for target page accepting multiple previous pages:

       1: using System;

       2: using System.Data;

       3: using System.Configuration;

       4: using System.Collections;

       5: using System.Web;

       6: using System.Web.Security;

       7: using System.Web.UI;

       8: using System.Web.UI.WebControls;

       9: using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

  

public partial class TargetPageMultipleSources : System.Web.UI.Page

{

    protected void Page_Load(object sender, EventArgs e)

    {

        if (PreviousPage != null)

        {

            if (PreviousPage is FirstSourcePage)

            {

                lblMessage.Text = ((FirstSourcePage)PreviousPage).Message;

            }

            else if (PreviousPage is SecondSourcePage)

            {

                lblMessage.Text = ((SecondSourcePage)PreviousPage).Message;

            }

            else

            {

                lblMessage.Text = "The previous page is unknown.";

            }

        }

        else

        {

            lblMessage.Text = "No previous page was detected.";

        }

    }

}

Markup for target page accepting multiple previous pages:

       1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="TargetPageMultipleSources.aspx.cs" Inherits="TargetPageMultipleSources" %>

       2: <%@ Reference Page="~/FirstSourcePage.aspx" %>

       3: <%@ Reference Page="~/SecondSourcePage.aspx" %>

       4: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

       5: <html xmlns="http://www.w3.org/1999/xhtml" >

       6:     <head runat="server">

       7:         <title>Target Page from Multiple Sources</title>

       8:     </head>

       9:     <body>

        <form id="frmMain" runat="server">

            <h1>TargetPageMultipleSources.aspx</h1>

            <div>

                <ul>

                    <li>

                        <a href="SingleSourcePage.aspx">SingleSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageSingleSource.aspx">TargetPageSingleSource.aspx</a>

                    </li>

                    <li>

                        <a href="FirstSourcePage.aspx">FirstSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="SecondSourcePage.aspx">SecondSourcePage.aspx</a>

                    </li>

                    <li>

                        <a href="TargetPageMultipleSources.aspx">TargetPageMultipleSources.aspx</a>

                    </li>

                </ul>

            </div>

            <div>

                <asp:Label ID="lblMessage" runat="server" />

            </div>

        </form>

    </body>

</html>

Conclusion

I've used this method several times with different websites I've worked on and it seems to do the trick for me. The comments are open if anyone else has another way they prefer to do this.