Infragistics WPF controls

WPF Validation tutorial for the rest of us. Learn to use IDataErrorInfo to automatically validate your views.

    WPF Validation for mere mortals I've recently jumped on the WPF bandwagon and I've fallen in love with this technology.  XAML is a fascinating animal indeed.  The declarative nature of the language leaves much to be explored.  There are many ways to solve the same problem.  On my quest for knowledge, I've been researching the intrinsic validation functionality of WPF.  Unfortunately, most every example I've ran across on blog posts and codeproject.com have been a bit too complex for my blood.  I find often that you need learn other subjects before you can begin to understand how the validation works.  Don't get me wrong, the examples are really nice.  However, when I'm learning something, I want a straight to the point example of the topic at hand.  It's with this idea in mind that I bring you a simple tutorial on WPF validation. I will be illustrating this example using the MVVM (Model-View-ViewModel) Pattern.   Click here to download the entire source WPFMVVMValidation.zip (74.08 kb)  Consider the following code  The view MainWindow.xaml <Window x:Class="ExceptionValidation.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:viewModel="clr-namespace:ExceptionValidation" Title="MainWindow" Height="350" Width="525" > <Window.Resources> <viewModel:MainWindowViewModel x:Key="mainViewModel"/> </Window.Resources> <StackPanel DataContext="{Binding Source={StaticResource mainViewModel }}"> <TextBlock>Enter total amount</TextBlock> <TextBox Width="200" Name="txtTotalAmount" > <Binding Path="[0].TotalAmount" ValidatesOnDataErrors="True"> <Binding.ValidationRules> <ExceptionValidationRule></ExceptionValidationRule> </Binding.ValidationRules> </Binding> </TextBox> <Button Content="Button" Height="28" Name="button1" Width="84" /> </StackPanel> </Window>     The viewmodel MainWindowViewModel.cs using System; using System.Collections.Generic; using System.Collections.ObjectModel; using System.Linq; using System.Text; using System.ComponentModel; namespace ExceptionValidation { class MainWindowViewModel : ObservableCollection<Product> { public MainWindowViewModel() { Add(new Product { TotalAmount = 3 }); } } }   The model Product.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.ComponentModel; namespace ExceptionValidation { public class Product : INotifyPropertyChanged , IDataErrorInfo { public event PropertyChangedEventHandler PropertyChanged; private int _totalAmount = 5; public int TotalAmount { get { return _totalAmount; } set { _totalAmount = value; OnPropertyChanged("TotalAmount"); } } public void OnPropertyChanged(string info) { PropertyChangedEventHandler handler = PropertyChanged; if (PropertyChanged != null) { handler(this, new PropertyChangedEventArgs(info)); } } public string Error { get { throw new NotImplementedException(); } } public string this[string columnName] { get { if (columnName == "TotalAmount") { bool valid = true; if (_totalAmount > 10) { valid = false; } if (!valid) { return "The total amount cannot exceed 10!"; } } return null; } } } } A brief introduction to MVVM  As you can see, we have a XAML view, a viewmodel class, and a model.  The Model is a representation of an object's data.  In this instance, we are modeling a Product.  The viewmodel is an object that handles the change notification between properties in the model and elements on the view.  XAML properties, events, and bindings have the ability to tunnel (down the tree) as well as bubble (up the tree).   Binding the ViewModel to the view. In order to bind the ViewModel to the view, we must make it accessible to the view via XAML.  To accomplish this, we first have to import the namespace in which the viewmodel exists.  Examine the following code. xmlns:viewModel="clr-namespace:ExceptionValidation" Here is the equivalent in c# using ExceptionValidation; Once we've imported the namespace for use, we then need to define our MainWindowViewModel as a Resource of the current window. <Window.Resources> <viewModel:MainWindowViewModel x:Key="mainViewModel"/> </Window.Resources> This allows us to declare an instance of the MainWindowViewModel class by using the associated Key "mainViewModel". Binding the ViewModel As stated before the ViewModel acts as a "go between" for the View and the Model.  In order for the view model to communicate with our XAML view, we will bind the ViewModel to the StackPanel's DataContext. <StackPanel DataContext="{Binding Source={StaticResource mainViewModel }}"> XAML's ability to tunnel properties down from parent to child will allow each element inside the stack panel to make use of the DataContext binding that we've just setup using the Window resource's key mainViewModel. ObservableCollection<T> The viewmodel inherits from ObservableCollection<Product>.  The ObservableCollection<T> generic class represents a collection that can be utilized by WPF databinding.  This is possible because the ObservableCollection<T> class raises an event when items are added and removed from the collection. INotifyPropertyChanged The model implements the INotifyPropertyChanged interface.  This interface provides an event in which to fire any time a model property is changed.  This event notifies the bound element in the view that the property has changed. public event PropertyChangedEventHandler PropertyChanged;   public void OnPropertyChanged(string info) { PropertyChangedEventHandler handler = PropertyChanged; if (PropertyChanged != null) { handler(this, new PropertyChangedEventArgs(info)); } }   IDataErrorInfo The magic behind WPF validation comes from the implementation of the IDataErrrorInfo interface.  The interface implements the following members.  The this[columnName] indexer implements the logic of the validation rule. //Not used by WPF public string Error { get { throw new NotImplementedException(); } } public string this[string columnName] { get { if (columnName == "TotalAmount") { bool valid = true; if (_totalAmount > 10) { valid = false; } if (!valid) { return "The total amount cannot exceed 10!"; } } return null; } } The following XAML code binds the TotalAmount property of the first Product in the viewmodel's internal collection to the Text property of the TextBox element.  The ValidatesOnDataErrors attribute tells the textbox binding to raise an event when there is a valadation error.  When the event is raised, the bound element's template is changed to a new visual style that places a Red rectangle around the border of the TextBox.  When the error is corrected, the original template is restored.  Binding.ValidatesOnDataErrors <TextBox Width="200" Name="txtTotalAmount" > <Binding Path="[0].TotalAmount" ValidatesOnDataErrors="True"> </Binding> </TextBox> In the provided example, if you enter a value greater than 10 into the text box and tab out of the textbox, you will see that an error is raised causing the red outline around the textbox.  If you correct the error by replacing the value with a number less than 10, the red outline will disappear. This concludes my tutorial on WPF validation.  This is the very basic of validation methods.  There are many other advanced tutorials on the subject.  My next tutorial will involve utilizing custom validation attributes from the System.ComponentModel namespace to handle WPF view validation. Thanks for reading! ~/Buddy James kick it on DotNetKicks.com  


How to configure mono 2.10, .NET 4.0 and ASP.NET MVC to run on an Ubuntu Apache web server.

The challenge... As per my previous post [post title here], I wanted to configure mono on my recently installed Ubuntu machine.  Specifically, I wanted to be able to use the latest .NET functionality as well as ASP.NET MVC integration with Apache.  In this post, I plan to provide the steps and resources in which I took to accomplish my goals. Let's start with the Ubuntu machine.... The Ubuntu desktop specifications The machine in which I've installed Ubuntu is an OLD machine that I had laying around the house.  My Android has more horsepower than this old Dell, however, Ubuntu 10.4 seems to operate at a perfectly acceptable capacity.  I plan to "refresh" my Linux skills and look for spare RAM to add to this machine before I upgrade to Ubuntu 12.04.  The recommended minimum requirements for Ubuntu 12.04 are as follows; [For installing] The minimum memory requirement for Ubuntu 12.04 is 384 MB of memory for Ubuntu Desktop. Note that some of your system's memory may be unavailable due to being used by the graphics card. If your computer has only the minimum amount of memory, the installation process will take longer than normal; however, it will complete successfully, and the system will perform adequately once installed. [For upgrading] While the minimum memory requirement for 32bit is 384 MB, a minimum of 512 MB is needed for the 64bit installation. On systems with only the bare minimum amount of memory, it is also strongly recommended to use the "Install Ubuntu" option as it uses less memory than the full live session. Ubuntu Desktop System Requirements for 12.04 LTS What's with all the aPtitude? As much as I love aptitude, I'm quite annoyed by the time it takes for source repositories to list packages as "stable".  I understand that this has nothing to do with the package manager itself and that the Ubuntu version carries more of the blame, even so, I wanted to simply apt-get install mono-complete, I would be stuck with mono 2.4.  Since I wanted to use   some newer functionality, I had some planning to do.  The overall process went a little something like this; Find a bash script that compiles all of the mono packages that I needed to get the job done. Execute the script and watch some T.V while I waited for the massive compile to complete. Move the Apache mono module configuration into the "available modules" folder to enable mod-mono under Apache. I needed to create an Apache virtual host configuration file with the mod-mono specific settings that are required. I had to prepare my file system to serve my ASP.NET applications (c:\inetpub\wwwroot\ for all you Windows natives). I needed to provide a simple solution to publish ASP.NET applications from Visual Studio on my Windows 7 machine to my Ubuntu web server. Finally I needed to restart apache2, publish a web application and test the fruits of my labor. BASHing mono into shape As I stated before, I wasn't going to apt-get install my way into the wonderful world of mono with all of the specific details that my target installation required.  Luckily, I found this post http://www.integratedwebsystems.com/2011/02/mono-2-10-install-script-for-ubuntu-fedora/  in which someone created a BASH script that would download all of the specific packages and compile the sources to produce the exact environment that I was after.  I'm sure  if I had used a modern PC it wouldn't have taken so long, never the less, the compilation was quite a time consuming task indeed!  The script was authored very well in that if there was an error detected, the script would break execution to make it easier for you to find what went wrong.  Fortunately, my compilation completed without a hitch!   Enabling mod_mono in Apache The BASH script had installed created the mod_mono.conf configuration file but I had to find it and copy it to the enabled modules directory so that Apache would recognize it. Here is the command that I executed from a terminal to copy the file to the proper location sudo cp mod_mono.conf /etc/apache2/mods-enabled Of course I had to find the configuration file before I could copy it sudo find -name mod_mono.conf With the configuration file in place, I restarted Apache to make sure all was well sudo service apache2 restart The service restarted successfully so I felt OK with what had been done so far. Creating the mono virtual host configuration file There is a webiste that will require you to fill in some input fields and click a button to generate this file the virtual host configuration with mono specific settings.  I merely had to modify one line of the file. The website is http://go-mono.com/config-mod-mono/ I simply used localhost as my server name and it generated the physical path of /srv/www/localhost. I used nano to edit the file and I modified the MonoDirectory line to point to the correct path of my mono_server4 binary's path which I was able to search and find to be /opt/mono-2.10/bin . Creating wwwroot, or /svr/www ... It was now time to prepare my file system to setup a home for my site hosting.  This basically involved creating some folders, setting permissions and creating an alias link or two. Create the directories sudo mkdir /srv/www sudo mkdir /srv/www/localhost Assign a root group to the folder sudo chown root:www-data /srv/www/localhost -R Change the directory attributes sudo chmod 775 /srv/www/localhost -R I then moved the virtual host site generated file to the appropriate path mv ~/Desktop/localhost.conf /etc/apache2/sites-available I then created a symbol link so I could refer to the vhost configuration file with leading zeros (Apache loads the configurations alphabetically). sudo ln -s ../sites-available/localhost.conf "000-localhost.conf" I restarted Apache, fired up firefox, browsed http://localhost and that's all it took...  I hope you enjoyed reading this article and I hope this helps someone configure ASP.NET MVC under Apache on Ubuntu using mono.  Until next time.. ~/Buddy James   kick it on DotNetKicks.com  


About the author

My name is Buddy James.  I'm a Microsoft Certified Solutions Developer from the Nashville, TN area.  I'm a Software Engineer, an author, a blogger (http://www.refactorthis.net), a mentor, a thought leader, a technologist, a data scientist, and a husband.  I enjoy working with design patterns, data mining, c#, WPF, Silverlight, WinRT, XAML, ASP.NET, python, CouchDB, RavenDB, Hadoop, Android(MonoDroid), iOS (MonoTouch), and Machine Learning. I love technology and I love to develop software, collect data, analyze the data, and learn from the data.  When I'm not coding,  I'm determined to make a difference in the world by using data and machine learning techniques. (follow me at @budbjames).  

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