Hi Guys,

Well after the last few months of building a commercial WPF app (and learning a lot along the way!) I’ve been generally delighted with the experience. A few things I feel could be a lot more polished, or a lot more thought out, but thems the breaks and we can only hope to see some improvements by Visual Studio 2012.

One of the trickiest and sadly, largest shortcoming of WPF I found was a trivial way to perform WPF form validation. It can get very complicated.

So I thought I might just post quickly some strategies I have implemented over the last few days and hopefully you guys can find some value in it and won’t need to go hunting yourselves.

I mainly illustrate a simple Username/Password TextBox Login validation scenario and to understand a bit more on how to set that up with the PasswordBoxAssistant class see the original post on this StackOverflow.com article: http://stackoverflow.com/questions/8942259/error-handling-in-wpf-passwordbox

My approach uses the standard IDataErrorInfo class.

Firstly, I put a call to a new method called OnDataUpdated() in each setter of my view-bound property, for instance:

        private string username;
        public string Username
        {
            get { return username; }
            set
            {
                username = value;
                OnDataUpdated();
            }
        }

        private string password;
        public string Password
        {
            get { return password; }
            set
            {
                password = value;
                OnDataUpdated();
            }
        }

Then inside OnDataUpdated() mark a private field boolean as true indicating data has changed for the first time (FormType was only necessary for my business case):

    private void OnDataUpdated()
    {
       dataChanged = true;
       // .. Any other universal RaisePropertyChanged() events you may want to call to get your UI into sync. Eg. RaisePropertyChanged(() => CanConfirm);
    }

Then in my IDataErrorInfo indexer property I do the following (I split it out so ValidForm() can be called manually to perform form validation too.

    public string this[string columnName]
            {
                get
                {
                    string result = null;
                    if (columnName == "Username")
                    {
                        // If other payment amounts have fully paid for balance, and cash amount has been entered, deny
                        if (!ValidForm(FormType.Step1, columnName))
                            result = "Please enter the username field.";
                    }
                    else if (columnName == "Password")
                    {
                        if (!ValidForm(FormType.Step1, columnName))
                            result = "Please enter the password field.";
                    }
                    return result;
                }
            }
        /// summary>
        /// Test if valid form.
        /// /summary>
        /// param name="formType">Specify which form we should validate./param>
        /// param name="columnName">If ommitted, entire form will be validated./param>
        /// returns>
        private bool ValidForm(FormType formType, string columnName = null)
        {
            // This field is used to denote when data has changed on the form.
            // If data has changed, we know we can activate any form validation.
            // We do not activate the form validation until after a user has typed
            // something in at least.
            if (!dataChanged) return true;
            var errors = false;
            if (formType == FormType.Step1 && ((string.IsNullOrEmpty(columnName) || columnName == "Username") && string.IsNullOrEmpty(Username)))
                errors = true;
            if (formType == FormType.Step1 && ((string.IsNullOrEmpty(columnName) || columnName == "Password") && string.IsNullOrEmpty(Password)))
                errors = true;
            return !errors;
        }

Works beautifully. Validation occuring great and most importantly bridges the gap on a large shortcoming — validation styles ONLY appear once the user commences editing the form.

If you want some extra icing on the cake, you can comment in my RaisePropertyChanged(() => CanConfirm); in the OnDataUpdated() method and bind that to your Confirm Button IsEnabled={Binding CanConfirm} with the associated property:

/// summary>
/// Can the user confirm step 1?
/// /summary>
public bool CanConfirm
{
    get { return ValidForm(FormType.Step1); }
}

and your button will only be enabled when your form is valid too.

Enjoy! and best of luck with the behemoth that is WPF.

I don’t have time right now, but I can put a working sample project up on request; just leave me a comment.

Hi Guys, I feel terrible I cannot blog as frequently now a days, so busy with so many projects on the go at the moment, including a couple of start-ups I’m working on.  But I wanted to quickly share with you probably the most valuable information I could give you in a short space of time; some awesome video resources on ASP.NET MVC and .NET in general from recent events! I find there is no better way to learn than through visual hands-on sometimes.

• MIX 11 ASP.NET MVC Videos (Las Vegas, Apr 12 – 14 2011) – Great selection of ASP.NET MVC videos and tons of other awesome HD content on .NET in there! Check it out!
• mvcConf 2 (Feb 2011) – ASP.NET MVC Conference gaining a lot of popularity and has some amazing content, ALL ON ASP.NET MVC!!! Watch them all and you will be an unstoppable MVC ninja!
• Check out the full selection of videos from recent events here, so much good content up on MSDN Channel9. Pay particular attention to the MIX 11 selection, PDC and TechEd stuff.

As always, if you are new to ASP.NET MVC, a great place to start is nothing other than www.asp.net/mvc.  Loads of great stuff, we’re up to ASP.NET MVC 3 now and it’s pretty darn awesome. Has links to text tutorials, sample projects and a great selection of videos.

If you want to hear about what happens in the ASP.NET MVC world as it happens, you’ll know doubt hear it from one of these blogs:

• Scott Guthrie (http://weblogs.asp.net/scottgu, VP for Microsoft Developer Division and manages the teams that build core .NET technologies)
• Phil Haack (http://www.haacked.com, Senior Program Manager at Microsoft on the ASP.NET team and builds ASP.NET MVC)
• Scott Hanselman (http://www.hanselman.com, Principal Program Manager for Microsoft and has a lot of great stuff to say, and a lot of jokes as well, check out any of his videos from events in the links above, very, very entertaining with some learning as well )

Are you getting this?

System.InvalidOperationException:
The null value cannot be assigned to a member with type System.Int64 which is a non-nullable value type.

On something like this?

var totalSize = query.Sum(x => x.Size);

This occurs because your LINQ property (in my case “Size”) is not nullable, and needs to be nullable because your Sum() operation could potentially iterate over a list which is empty yielding your LINQ property value to be null.
Of course you can’t Sum() null as we know or the universe would explode, so try this instead:

var totalSize = query.Sum(x => (long?) x.Size);

This may very well just be a LINQ to SQL thing, but I am not sure. Maybe somebody else out there in the wide world web can enlighten me!

Best of luck!

Just heard news of a sweet new website dedicated to Theming and Styling Visual Studio, called “StudioStyles” now that’s my kinda site.  Go check it out, tons of themes to choose from if your VS IDE is looking kinda drab or you’re sick of looking at that same old blue and white…

I also just updated my own Desert Nights theme variation, “Desert Nights Reloaded”; it’s now available for VS 2010 as well as VS 2008 with ReSharper 5 color coding support! Cool! So go get it, officially from my blog or go check it out on StudioStyles! What are you waiting for !?!

Not much else happening in blogger-verse right now, but I will let you know if anything exciting happens…

Every now and then I find myself needing to set multiple values to an enum object and test this later on, synonymously I usually find myself also scouring the net on the best practice on how to set, access and test these enum flags

So today I thought I would post a definitive reference I found on the net..

Specify flag-annotated enum:

[Flags]
public enum Column
{
None = 0,
Priority = 1 << 0,
Customer = 1 << 1,
Contract = 1 << 2,
Description = 1 << 3,
Tech = 1 << 4,
Created = 1 << 5,
Scheduled = 1 << 6,
DueDate = 1 << 7,
All = int.MaxValue
};

The [Flags] attribute allows you to do this:

Column MyColumns = Column.Customer | Column.Contract;

To check if contains flag:

if ((MyColumns & Column.Customer) != 0)

To check if has flag or higher:

if (MyColumns >= Column.Customer)

To check if has flag or lower:

if (MyColumns <= Column.Customer)

To set a flag:

MyColumns |= Column.Tech;

To clear a flag:

MyColumns &= ~Column.Tech;

To toggle (flip) a flag:

MyColumns ^= Column.Contract;

To clear all flags:

MyColumns = Column.None;

To set all flags:

MyColumns = Column.All;

To set all flags EXCEPT one or more:

MyColumns = Column.All ^ Column.Tech ^ Column.Status;

Credit to Jeremy Lundy for the comprehensive write up.