Peter Johnson's Blog

ASP.NET and other technologies

  • MVC's Html.DropDownList and "There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key '...'

    ASP.NET MVC's HtmlHelper extension methods take out a lot of the HTML-by-hand drudgery to which MVC re-introduced us former WebForms programmers. Another thing to which MVC re-introduced us is poor documentation, after the excellent documentation for most of the rest of ASP.NET and the .NET Framework which I now realize I'd taken for granted.


  • How to create a new WCF/MVC/jQuery application from scratch

    As a corporate developer by trade, I don't get much opportunity to create from-the-ground-up web sites; usually it's tweaks, fixes, and new functionality to existing sites. And with hobby sites, I often don't find the challenges I run into with enterprise systems; usually it's starting from Visual Studio's boilerplate project and adding whatever functionality I want to play around with, rarely deploying outside my own machine. So my experience creating a new enterprise-level site was a bit dated, and the technologies to do so have come a long way, and are much more ready to go out of the box. My intention with this post isn't so much to provide any groundbreaking insights, but to just tie together a lot of information in one place to make it easy to create a new site from scratch.


  • MVC 4 and the App_Start folder

    I've been delving into ASP.NET MVC 4 a little since its release last month. One thing I was chomping at the bit to explore was its bundling and minification functionality, for which I'd previously used Cassette, and been fairly happy with it. MVC 4's functionality seems very similar to Cassette's; the latter's CassetteConfiguration class matches the former's BundleConfig class, specified in a new directory called App_Start.


  • Unity throws SynchronizationLockException while debugging

    I've found Unity to be a great resource for writing unit-testable code, and tests targeting it. Sadly, not all those unit tests work perfectly the first time (TDD notwithstanding), and sometimes it's not even immediately apparent why they're failing. So I use Visual Studio's debugger. I then see SynchronizationLockExceptions thrown by Unity calls, when I never did while running the code without debugging. I hit F5 to continue past these distractions, the line that had the exception appears to have completed normally, and I continue on to what I was trying to debug in the first place.

    In settings where Unity isn't used extensively, this is just one amongst a handful of annoyances in a tool (Visual Studio) that overall makes my work life much, much easier and more enjoyable. But in larger projects, it can be maddening. Finally it bugged me enough where it was worth researching it.


  • MVC's IgnoreRoute syntax

    I've had an excuse to mess around with custom route ignoring code in ASP.NET MVC, and am surprised how poorly the IgnoreRoute extension method on RouteCollection (technically RouteCollectionExtensions, but also RouteCollection.Add, and RouteCollection.Ignore which was added in .NET 4) is documented, both in the official docs by Microsoft, and various bloggers and forum participants who have been using it, some for years.


  • SQL Server 2005/2008's TRY/CATCH and constraint error handling

    I was thrilled that T-SQL finally got the TRY/CATCH construct that many object-oriented languages have had for ages. I had been writing error handling code like this:

    BEGIN TRANSACTION TransactionName


    -- Core of the script - 2 lines of error handling for every line of DDL code
    ALTER TABLE dbo.MyChildTable DROP CONSTRAINT FK_MyChildTable_MyParentTableID
    IF (@@ERROR <> 0)
        GOTO RollbackAndQuit


    COMMIT TRANSACTION TransactionName
    GOTO EndScript

    -- Centralized error handling for the whole script
        ROLLBACK TRANSACTION TransactionName
        RAISERROR('Error doing stuff on table MyChildTable.', 16, 1)



    ...which gets pretty ugly when you have a script that does 5-10 or more such operations and it has to check for an error after every one. With TRY/CATCH, the above becomes:

    BEGIN TRANSACTION TransactionName;



    -- Core of the script - no additional error handling code per line of DDL code
    ALTER TABLE dbo.MyChildTable DROP CONSTRAINT FK_MyChildTable_MyParentTableID;


    COMMIT TRANSACTION TransactionName;


    -- Centralized error handling for the whole script
        ROLLBACK TRANSACTION TransactionName;

        DECLARE @ErrorMessage NVARCHAR(4000) = 'Error creating table dbo.MyChildTable. Original error, line [' + CONVERT(VARCHAR(5), ERROR_LINE()) + ']: ' + ERROR_MESSAGE();
        DECLARE @ErrorSeverity INT = ERROR_SEVERITY();
        RAISERROR (@ErrorMessage, @ErrorSeverity, @ErrorState)


    Much cleaner in the body of the script; we have to do more work in the CATCH (wouldn't it be nice if T-SQL had a THROW statement like C# to rethrow the exact same error that was caught?), but the core of the script that makes DDL changes is cleaner and more readable. The only serious downside I've found so far is when dropping a constraint, and you get a message like this without TRY/CATCH:

    Msg 3728, Level 16, State 1, Line 1
    'FK_MyChildTable_MyParentTableID' is not a constraint.
    Msg 3727, Level 16, State 0, Line 1
    Could not drop constraint. See previous errors.

    (In this case I'd check for the constraint before trying to drop it; this is just for illustration. One I've seen more often is trying to drop a primary key and recreate it on a parent table when there are foreign keys on child tables that reference the parent.)

    TRY/CATCH shortens the above error to only "Could not drop constraint. See previous errors." with no previous errors shown. Now, some research will reveal why it couldn't drop the constraint, but TRY/CATCH is supposed to make error handling easier and more straightforward, not more obscure. The "See previous errors" line has always struck me as a lazy error message--I bet there's a story amongst seasoned SQL Server developers at Microsoft as to why this throws two error messages instead of one--so I imagine the real problem is in that dual error message more than the TRY/CATCH construct itself as it's implemented in T-SQL.

    If anyone has a slick way to get that initial Msg 3728 part of the error, I'm all ears; I've seen several folks ask this question and not one answer yet.


  • Windows Workflow Foundation (WF) and things I wish were more intuitive

    I've started using Windows Workflow Foundation, and so far ran into a few things that aren't incredibly obvious. Microsoft did a good job of providing a ton of samples, which is handy because you need them to get anywhere with WF. The docs are thin, so I've been bouncing between samples and downloadable labs to figure out how to implement various activities in a workflow.

    Code separation or not? You can create a workflow and activity in Visual Studio with or without code separation, i.e. just a .cs "Component" style object with a Designer.cs file, or a .xoml XML markup file with code behind (beside?) it. Absence any obvious advantage to one or the other, I used code separation for workflows and any complex custom activities, and without code separation for custom activities that just inherit from the Activity class and thus don't have anything special in the designer. So far, so good.

    Workflow Activity Library project type - What's the point of this separate project type? So far I don't see much advantage to keeping your custom activities in a separate project. I prefer to have as few projects as needed (and no fewer). The Designer's Toolbox window seems to find your custom activities just fine no matter where they are, and the debugging experience doesn't seem to be any different.

    Designer Properties - This is about the designer, and not specific to WF, but nevertheless something that's hindered me a lot more in WF than in Windows Forms or elsewhere. The Properties window does a good job of showing you property values when you hover the mouse over the values. But they don't do the same to find out what a control's type is. So maybe if I named all my activities "x1" and "x2" instead of helpful self-documenting names like "listenForStatusUpdate", then I could easily see enough of the type to determine what it is, but any names longer than those and all I get of the type is "System.Workflow.Act" or "System.Workflow.Compone". Even hitting the dropdown doesn't expand any wider, like the debugger quick watch "smart tag" popups do when you scroll through members. The only way I've found around this in VS 2008 is to widen the Properties dialog, losing precious designer real estate, then shrink it back down when you're done to see what you were doing. Really?

    WF Designer - This is about the designer, and I believe is specific to WF. I should be able to edit the XML in a .xoml file, or drag and drop using the designer. With WPF (at least in VS 2010 Ultimate), these are side by side, and changes to one instantly update the other. With WF, I have to right-click on the .xoml file, choose Open With, and pick XML Editor to edit the text. It looks like this is one way where WF didn't get the same attention WPF got during .NET Fx 3.0 development.

    Service - In the WF world, this is simply a class that talks to the workflow about things outside the workflow, not to be confused with how the term "service" is used in every other context I've seen in the Windows and .NET world, i.e. an executable that waits for events or requests from a client and services them (Windows service, web service, WCF service, etc.).

    ListenActivity - Such a great concept, yet so unintuitive. It seems you need at least two branches (EventDrivenActivity instances), one for your positive condition and one for a timeout. The positive condition has a HandleExternalEventActivity, and the timeout has a DelayActivity followed by however you want to handle the delay, e.g. a ThrowActivity. The timeout is simple enough; wiring up the HandleExternalEventActivity is where things get fun. You need to create a service (see above), and an interface for that service (this seems more complex than should be necessary--why not have activities just wire to a service directly?). And you need to create a custom EventArgs class that inherits from ExternalDataEventArgs--you can't create an ExternalDataEventArgs event handler directly, even if you don't need to add any more information to the event args, despite ExternalDataEventArgs not being marked as an abstract class, nor a compiler error nor warning nor any other indication that you're doing something wrong, until you run it and find that it always times out and get to check every place mentioned here to see why. Your interface and service need an event that consumes your custom EventArgs class, and a method to fire that event, but creating the EventArgs by passing in null for the sender parameter--if you pass in this, as one normally does when firing events, for some reason the HandleExternalEventActivity won't see that the event has fired. Then you need to call that method from somewhere. Then you get to hope that you did everything just right, or that you can step through code in the debugger before your Delay timeout expires. Yes, it's as much fun as it sounds.

    TransactionScopeActivity - I had the bright idea of putting one in as a placeholder, then filling in the database updates later. That caused this error:

    The workflow hosting environment does not have a persistence service as required by an operation on the workflow instance "[GUID]".

    ...which is about as helpful as "Object reference not set to an instance of an object" and even more fun to debug. Google led me to this Microsoft Forums hit, and from there I figured out it didn't like that the activity had no children. Again, a Validator on TransactionScopeActivity would have pointed this out to me at design time, rather than handing me a nearly useless error at runtime. Easily enough, I disabled the activity and that fixed it.

    I still see huge potential in my work where WF could make things easier and more flexible, but there are some seriously rough edges at the moment. Maybe I'm just spoiled by how much easier and more intuitive development elsewhere in the .NET Framework is.


  • Migrating from VS 2005 to VS 2008

    I recently helped migrate a ton of code from Visual Studio 2005 to 2008, and .NET 2.0 to 3.5. Most of it went very smoothly; it touches every .sln, .csproj, and .Designer.cs file, and puts a bunch of junk in Web.Configs, but rarely encountered errors. One thing I didn't expect was that even for a project running in VS 2008 but targeting .NET Framework 2.0, it will still use the v3.5 C# compiler. As such, it does behave a bit differently than the 2.0 compiler, even when targeting the 2.0 Framework.

    One piece of code used an internal custom EventArgs class, that was consumed via a public delegate. This code compiled fine using the 2.0 C# compiler, but the 3.5 compiler threw this error:

    error CS0059: Inconsistent accessibility: parameter type 'MyApp.Namespace.MyEventArgs' is less accessible than delegate 'MyApp.Namespace.MyEventHandler'

    It's a goofy situation, the error makes perfect sense, and it was easy to correct (I made both internal), but I expected VS 2008 would use the compiler to match whatever the target .NET Framework version was. I wouldn't have expected any compilation errors it didn't have before conversion, not until I changed the targeted Framework version.

    Another funny error happened around code analysis. Code analysis ran fine in VS 2005, but in VS 2008, it threw this error (compilation error, not a code analysis warning):

    Running Code Analysis...
    C:\Program Files\Microsoft Visual Studio 9.0\Team Tools\Static Analysis Tools\FxCop\FxCopCmd.exe /outputCulture:1033 /out:"bin\Debug\MyApp.Namespace.MyProject.dll.CodeAnalysisLog.xml" /file:"bin\Debug\MyApp.Namespace.MyProject.dll" /directory:"C:\MyStuff\MyApp.Namespace.MyProject\bin\Debug" /directory:"c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727" /directory:"..\..\..\Lib" /rule:"C:\Program Files\Microsoft Visual Studio 9.0\Team Tools\Static Analysis Tools\FxCop\Rules" /ruleid:-Microsoft.Design#CA1012 /ruleid:-Microsoft.Design#CA2210 ... /searchgac /ignoreinvalidtargets /forceoutput /successfile /ignoregeneratedcode /saveMessagesToReport:Active /targetframeworkversion:v2.0 /timeout:120 MSBUILD : error : Invalid settings passed to CodeAnalysis task. See output window for details.
    Code Analysis Complete -- 1 error(s), 0 warning(s)
    Done building project "MyApp.Namespace.MyProject.csproj" -- FAILED.

    I especially like the "See output window for details," which 1. screams of a Visual Studio hack as it is, and 2. doesn't actually give me any more details in this particular case, though Google tells me that other people do get more information in the output window.

    I noticed Debug and Release modes both had code analysis enabled (I think switching Framework versions swapped them on me and I accidentally enabled it in Release mode), and Release mode wasn't erroring out but Debug was. I looked at the difference in the csproj file, and in the FxCopCmd.exe calls, and the key seemed to be the /ruleid parameters (bolded), of which there were a ton in Debug but not Release. Presumably this is because I disabled some of the rules in the project properties, so I tried enabling them all. The number of /ruleid params went down, but it still gave the same error. The Code Analysis tab in project properties looked the same between Debug and Release.

    Finally I unloaded the project, edited the csproj file (I'm glad I found out how to do this within VS, instead of exiting VS and editing it in Notepad), and removed this line, which was present in the Debug PropertyGroup element but not the Release one:


    Code analysis then ran successfully. I imagine this solution isn't ideal for everyone, if you want to enable/disable particular rules, and it's not ideal for us long-term, but it did allow us to keep code analysis enabled without the build failing.


  • Windows 7 rocks!

    I bought my current PC almost three years ago. I've had my own PC for 15 years or so, and, aside from my first desktop and a laptop I only use when traveling, that was the only time I've bought a whole PC, rather than buying parts and assembling my own (a Frankenputer as former coworkers affectionately referred to them). Like many of my colleagues who work in Microsoft technologies, I looked into buying a Dell, and they had a fine deal, and more importantly, they had finally started selling AMD processors, which I can proudly say without qualification is the only CPU in any computer I've owned. I configured one with a dual core, 64-bit processor, and all sorts of new technologies I'd never heard of but were (and appear to still be) the latest and the greatest. ("What's SATA? We use PCI for video again?" I asked myself.)

    Windows Vista had RTM'd and was weeks from retail availability, and my PC included a deal to upgrade once Microsoft let Dell send upgrade discs. My PC had a rather small (160 GB, I think) hard drive, which I intended to replace with a 500 GB or so once Vista came out, installing it there fresh instead of trying to upgrade Windows--Windows upgrades have never worked so well for me, whereas fresh installs are fine. Then I heard all the complaining about Vista, and decided to hold off. I ran low on space before Vista SP1 came out, so got that second hard drive anyway and kept my photos there. From then on, Windows XP Professional worked "well enough" so I stuck with it.

    Things got bad a couple months before Windows 7 came out. First, Norton AntiVirus misbehaved. To be fair, the program was about 6-7 years old; I kept it around because it seemed to work well enough, I got it free as a student, and virus definition upgrades were free. Then I noticed the dates on the definitions went from a few days ago, to the middle of 1999. It still changed every week, and still found upgrades, so I'm guessing it was just a bug in how it displayed the definitions date, but still made me nervous, as did the prospect of uninstalling old and installing new virus scanners.

    Roxio was the next to act up. After Microsoft paved the way with Windows Update, suddenly every software manufacturer was convinced their product was just as important to check at least every week for updates, and the updates, just as urgent. Eventually I got Apple to quit bugging me to install Bonjour and Safari, but I couldn't get Roxio (or, perhaps more accurately, InstallShield Update Manager which came with Roxio) to quit prompting me to check for updates on the 0 products I had told it to check. I googled and finally found a tool I could use to uninstall that piece of it, without uninstalling Roxio, on InstallShield's support site.

    That was a mistake. It stopped prompting me, but added about 3 minutes from when Windows comes up after I start my PC, until my computer was usable, and in the meantime, Norton was disabled, Windows Firewall was disabled, and programs wouldn't start. Add to this a nagging problem where my SD/CompactFlash card reader thinks it's USB 1.x intermittently, and the ugly way Windows Search was grafted onto Windows XP, and the fact that XP (and earlier versions of Windows--not sure about 7 yet) just slows down after a couple years, and I knew it was time to upgrade once Windows 7 came out.

    The more I learned about Windows 7 (and, to be fair, much of it was new in Vista and largely unchanged in 7, but I'd barely ever used Vista), the more I liked it. The way search worked much faster, more efficiently, and was integrated into everything, even the Start Menu (no more reorganizing each program's 20 or so icons so I could find the ones I actually wanted! no more sorting alphabetically every time I install a new program!)... An overhauled Windows Explorer including a new Libraries feature (not in Vista) that didn't force you to keep everything in your profile for Windows to like it... and finally getting to install 4 GB of memory and take advantage of my 64-bit processor!

    After Microsoft decided one day the long-activated Windows XP installation on my laptop was no longer valid, with no explanation why, I wasn't going to chance them deciding the same thing on my main PC, so I broke down and got the full version of Windows 7. I opted for Home Premium after finding little difference between Home Premium and Professional that I cared about, since Home Premium should be able to run IIS, and if it can't, Visual Studio 2008's web server should be enough for what I need on this PC. I installed it not quite a month ago, replacing NAV and Ad-Aware with the new free and highly-rated Microsoft Security Essentials, and Roxio with--well, either what's built into Windows 7 or my favorite CD ripper Easy CD-DA Extractor, and it's great. I can work the way I want to, customize things as much as I need (you're close, iPhone, but not quite there), and boy is Aero pretty. I'm a sucker for eye candy (I do have an iPhone).

    The search works great. I was leery about using Windows Search (installed against your will by Office 2007) or Google Desktop Search (must be unchecked in order to not install with every Adobe program and tons of others) add-ons for Windows XP; that sort of thing just seems like too core a functionality to get some freebie add-on to handle. Windows XP's built-in search might suck, but it usually found what I wanted, and didn't take too long. Sure enough, Windows 7 search works instantly, and if you copy over a ton of files it hasn't indexed, as I did when I wiped my hard drive to install 7 then copied back from my backup, it might not find everything right away, but it will after it spends a few minutes indexing them. And, as advertised, it doesn't slow me down while I'm using the PC; I haven't heard my hard drive crank once while I've been writing this long post. By default, it only indexes in your Libraries, and MS suggests anything you want indexed, you put in a Library. That put me off at first--what if I need to search for a system file or something?--but really, the vast majority of stuff I search for slots fine in either the Documents, Music, or Pictures Libraries. Moving from XP to 7 takes some adjustment, but I gave it a chance, and I'm quite happy with it. And if I do ever need to do a search for a certain DLL, it's easy enough to add folders to the list of what's indexed. I don't even have to dig into Administrative Tools and various Control Panel applets and System Tools folders, wondering where Microsoft has hidden that options screen in this version, thanks to the Start Menu search feature. I just click the Windows key, type "index", and it's the first option:


    Just like searching on the web, the content is what matters; its physical location is now much less important. You just type in a word or two and it figures out what you want, no matter where it is.

    Another great and long-overdue improvement is the Windows Explorer dialogs for long-running file operations--deleting, copying, moving. It gives you more of the path, and best of all, an accurate estimate of how long it will take, and the rate at which it's copying files! No more operations where it takes 45 seconds for the first part and 23987105 minutes for the last part.

    The most annoying thing I've found so far is based on principle, and not any difference I've observed. Occasionally, programs crash. Two that I use often, Mozilla Firefox and IrfanView, have each crashed once. (Amusingly, both when they tried to start up the Apple QuickTime plug-in; I have a few things to say about my iTunes migration experience, but that'll have to wait for another post.) But once is all it takes in Windows 7, before Program Compatibility Assistant (PCA) kicks in and applies some sort of mysterious sanctions to the offender.


    Obviously I was curious about what those "settings" it applied were, and how to grant amnesty for first-time offenses. That link has a help article with those exact questions. And the answer? "It depends," and "go to TechNet and teach yourself about group policy," respectively. (In their words, "Adjustments to program compatibility features can be made by using Group Policy. For advanced information on how to use Group Policy, go to the Microsoft website for IT professionals.") Seriously? A little more googling and I found out that you can dig into it, or disable PCA altogether, using Group Policy Editor, which... doesn't come with Home Premium. So it sounds like my only choice is manually editing the registry. I can't even find out what PCA changed about how those programs run; a few articles allude to ominous performance degradations in order to ensure stability. Windows 7 addresses so many things that bugged me about XP and earlier versions; it's a shame they dropped the ball on this one. To be fair, it seems that this is how Vista functioned, and Windows 7 didn't make it worse, but didn't improve it, either.

    But, to summarize, I'm thrilled with Windows 7, and with 64-bit computing, though I'm a little surprised more programs aren't 64-bit (Firefox and Flash Player, I'm looking at you). Oh well--we had the same problem switching from 16-bit to 32-bit, but I'm glad enough software and hardware is there, that I can upgrade and work just fine until the rest of it makes it.