Posts Tagged C#

C#: ToString To Report all Properties Even Private Ones Via Reflection

At some point one needs to view all the properties of an instance outside of a debugger such as for a unit test reporting the results or possibly a console application informing its status to the output. To achieve the results one overrides ToString() and by hand writes the information of the instance’s properties and their values to the output string. This can become cumbersome if the class instance is changing or when one realizes that the time ratio of creating such a reporting operation verses the size of what is being reported can lead to valuable time taken away from the developer.

This article demonstrates a C# extension which will take any class instance and report any non null properties as well as any string lists. The goal of the report is to provide information on the standard properties (string, int, datetime, etc) as well as string lists and ignores any  complex objects. Also provided is the ability to show the non-public properties.

For the resulting visual list, the code lines up the output report in key value pairs where the largest character count key name (the property name reported) will be spaced out along with all other names.

Here is an example result of a class instance with differing properties. Note that MemberOfAsList is a List<string> property which internally splits out the property MemberOf string (by its comma) into a list. This extension shows the list as a string.join of ", ".

DistinguishedName : CN=Write Frank,OU=Test,OU=Acme Industries,DC=amce-co,DC=acme,DC=net
CommonName        : Write Frank Lloyd
MemberOf          : CN=2042_Identity,CN=UserIdentities,CN=AlphaVision,DC=acme-co,DC=acme,DC=net
MemberOfAsList    : CN=2042_Identity, CN=UserIdentities, CN=AlphaVision, DC=acme-co, DC=acme, DC=net
otherTelephone    : 303-555-555
Name              : Wright Frank
WhenChanged       : 3/17/2014 9:04:06 PM
LogonCount        : 0

Extension Method

The following is an extension method whose goal is to reflect the type being passed in, determine the sizing of the data for output and then reports the properties each on a different line. String lists values are specified by a , (comma and space) separator between each value.

public static string ReportAllProperties<T>(this T instance) where T : class
{

    if (instance == null)
        return string.Empty;

    var strListType = typeof(List<string>);
    var strArrType  = typeof(string[]);

    var arrayTypes   = new[] { strListType, strArrType };
    var handledTypes = new[] { typeof(bool), typeof(Int32), typeof(String), typeof(DateTime), typeof(double), typeof(decimal), strListType, strArrType };

    var validProperties = instance.GetType()
                                  .GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)
                                  .Where(prop => handledTypes.Contains(prop.PropertyType))
                                  .Where(prop => prop.GetValue(instance, null) != null)
                                  .ToList();

    var format = string.Format("{{0,-{0}}} : {{1}}", validProperties.Max(prp => prp.Name.Length));

    return string.Join(
             Environment.NewLine,
             validProperties.Select(prop => string.Format(format, 
                                                          prop.Name,
                                                          (arrayTypes.Contains(prop.PropertyType) ? string.Join(", ", (IEnumerable<string>)prop.GetValue(instance, null))
                                                                                                  : prop.GetValue(instance, null)))));
}

Usage

public override string ToString()
{
    return ( this.ReportAllProperties() );
}

Test & Results

var test = new MyClass("Admin") { Name = "Omegaman", 
                                  ID = 1,  
                                  StartDate = DateTime.Now,
                                  AccessPoints = new List<string> { "Alpha", "Beta", "Gamma" },
                                  WeekDays = new string[]{ "Mon", "Tue" }
                                 };

 Console.WriteLine (test.ToString());

/*
Name         : Omegaman
ID           : 1
Role         : Admin
AccessPoints : Alpha, Beta, Gamma
WeekDays     : Mon, Tue
StartDate    : 3/18/2014 12:16:07 PM
*/

....

public class MyClass
{
    public string Name               { get; set; }
    public int ID                    { get; set; }
    private string Role              { get; set; }
    public List<string> AccessPoints { get; set; }
    public string[] WeekDays         { get; set; }    
    public DateTime StartDate        { get; set; }

    public MyClass(string role)
    {
        Role = role;
    }

    public override string ToString()
    {
       return ( this.ReportAllProperties() );
    }

}

Done!

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C# Linq: Find Missing Values in a Sequence of Numbers and Other Sequence Related lists as IEnumerable Extensions

Water bubble and wavesI recently had a need to determine if a sequence of integers was solid, not broken, and whether it contained a gap of any missing numbers to report to the end user. I researched the issue and was dismayed that the examples found on the internet seemed to have unnecessary overheads of copied arrays or other artifacts and were too cumbersome for my needs. From that I wrote these C# extensions which work for any .Net above 3.5. Below I document the extension methods to get the missing numbers of a sequence, quickly determine if a sequence is broken and finally report where the existing numbers before the break of the sequence. See the end for the whole extension class for easier copying.

Problem Definition

If one has a set of numbers say

{ 2, 4, 7, 9 }

it has a broken sequence because there are missing numbers from the set 2-9. Those missing numbers are:

{ 3, 5, 6, 8 }

Find Missing Numbers In a Sequence

This method is the one I created first. It uses the Linq Aggregate extension to enumerate over the numbers in the set. If there is a gap which is greater than 1 between the numbers (the difference below is > 0 but same concept) then it reports the numbers missing between the two.

public static IEnumerable<int> SequenceFindMissings(this IList<int> sequence)
{

    var missing = new List<int>();

    if ((sequence != null) && (sequence.Any()))
    {
        sequence.Aggregate((seed, aggr) =>
                            {
                                var diff = (aggr - seed) - 1;

                                if (diff > 0)
                                    missing.AddRange(Enumerable.Range((aggr - diff), diff));

                                return aggr;
                            });
    }

    return missing;
}

Quickly Determine Broken Sequence

Is the sequence broken from the first number to the last in the set?

public static bool IsSequenceBroken(this IEnumerable<int> sequence)
{
    bool broken = false;

    if (sequence != null) 
    {
        var sequenceAsList = sequence.ToList();

        if (sequenceAsList.Any())
        {
            int lastValue = sequence.First();

            broken = sequence.Any(value =>
                                    {
                                        if ((value - lastValue) > 1)
                                            return true;

                                        lastValue = value;

                                        return false;
                                    }); 
        }
    }

    return broken;
}

Report Last Valid Number Before The Break

This is useful in situations where one needs to report where the break happens, say the user is editing in a grid and one highlights the existing number which precedes the missing number(s).

Example here returns a 2 and 5 which are the numbers which precede the break.

   (new List() { 1, 2, 4, 5, 7, 8}).SequenceReportMissingsBreakStarts()

Here is the method:

public static IEnumerable<int> SequenceReportMissingsBreakStarts(this IList<int> sequence)
{

    var breaks = new List<int>();

    if ((sequence != null) && (sequence.Any()))
    {

        sequence.Aggregate((seed, aggr) =>
                            {
                                var diff = (aggr - seed) - 1;

                                if (diff > 0)
                                    breaks.Add(seed);
                                return aggr;
                            });
    }

    return breaks;
}

Full Extension Source With Comments

Here is the code for an easier copy

public static class SequenceExtensions
{
    /// <summary>
    /// Take a sequence of numbers and if there are any gaps greater than 1 between the numbers,
    /// report true.
    /// </summary>
    /// <param name="sequence">A set of numbers to check.</param>
    /// <returns>True if the there is a break in the sequence of numbers.</returns>
    public static bool IsSequenceBroken(this IEnumerable<int> sequence)
    {
        bool broken = false;

        if (sequence != null)
        {
            var sequenceAsList = sequence.ToList();

            if (sequenceAsList.Any())
            {
                int lastValue = sequence.First();

                broken = sequence.Any(value =>
                                        {
                                            if ((value - lastValue) > 1)
                                                return true;

                                            lastValue = value;

                                            return false;
                                        });
            }
        }

        return broken;
    }

    /// <summary>
    /// Take a sequence of numbers and report the missing numbers. Stop at first break found.
    /// </summary>
    /// <param name="sequence">Set of Numbers</param>
    /// <returns>True of sequence has missing numbers</returns>
    public static IEnumerable<int> SequenceFindMissings(this IList<int> sequence)
    {

        var missing = new List<int>();

        if ((sequence != null) && (sequence.Any()))
        {
            sequence.Aggregate((seed, aggr) =>
                                {
                                    var diff = (aggr - seed) - 1;

                                    if (diff > 0)
                                        missing.AddRange(Enumerable.Range((aggr - diff), diff));

                                    return aggr;
                                });
        }

        return missing;

    }

    /// <summary>
    /// A missing break start in a sequence is where the drop off occurs in the sequence.
    /// For example 3, 5, has a missing break start of the #3 for #4 is the missing.
    /// </summary>
    /// <param name="sequence">Set of Numbers</param>
    /// <returns>The list of break numbers which exist before the missing numbers.</returns>
    public static IEnumerable<int> SequenceReportMissingsBreakStarts(this IList<int> sequence)
    {

        var breaks = new List<int>();

        if ((sequence != null) && (sequence.Any()))
        {

            sequence.Aggregate((seed, aggr) =>
                                {
                                    var diff = (aggr - seed) - 1;

                                    if (diff > 0)
                                        breaks.Add(seed);
                                    return aggr;
                                });
        }

        return breaks;

    }
}

Hope this helps!

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Xaml: ViewModel Main Page Instantiation and Loading Strategy for Easier Binding.

BasicBindingUpdate 11.07.2013 : Added ICommanding example.
Update 10.25.2013 : Added how to use the CallerMemberName attribute with INotifyPropertyChanged in .Net 4.

While answering a question on StackOverflow I ran across a situation where the user was having troubles due to binding to a view model which was statically initiated in Xaml. While there is nothing wrong with creating the VM in Xaml, it can miss some benefits for most control and page situations where the all controls want to access one source of data. This article describes and provides example code to creating the view model in the code behind which I tend to prefer over the others methods.

Create a .Net 4 and Above VM

The view model adheres to the standard where it implements INotifyPropertyChange. The following ViewModel implements it using the .Net 4.5 way with the CallerMemberName attribute which saves us from having to explicitly define it on every member call. (If you are using .Net 4, add the Nuget Package: Microsoft BCL into you project to use CallerMemberName attribute).

Note for reference there is a situation below where we actually do specify the property name but it is to create in a change notification on another property.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace SO_WPF.ViewModels {

public class MainVM : INotifyPropertyChanged 
{

    private List<string> _Members;
    private int _MemberCount;
    private bool _IsMembershipAtMax;
    public bool IsMembershipAtMax 
    {
        get { return MemberCount > 3; }
    }
    public int MemberCount 
    { 
        get { return _MemberCount; }
        set
        {
            _MemberCount = value; 
            OnPropertyChanged();
            OnPropertyChanged("IsMembershipAtMax");
        } 
    }

    public List<string> Members 
    { 
        get { return _Members; }
        set { _Members = value; OnPropertyChanged(); } 
    }
    public MainVM()
    {
        // Simulate Asychronous access, such as to a db.

        Task.Run(() =>
                    {
                        Members = new List<string>() {"Alpha", "Beta", "Gamma", "Omega"};
                        MemberCount = Members.Count;
                    });
    }
    /// <summary>Event raised when a property changes.</summary>
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>Raises the PropertyChanged event.</summary>
    /// <param name="propertyName">The name of the property that has changed.</param>
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

}
}

Main Page Code Behind

We now need to hook up the main page view model to the main page. To do that we will do two things, one, make a non INotifyPropertyChanged property on the class which will hold our view model. Two we will instantiate it, hook it up to the page’s data along with our property. Doing that ensures that everything on our page will get access to our view model, thanks to the data context and how controls inherit their parents data context.

using SO_WPF.ViewModels;

namespace SO_WPF
{
    public partial class MainWindow : Window
    {

        public MainVM ViewModel { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            // Set the windows data context so all controls can have it.
            DataContext = ViewModel = new MainVM();

        }

    }
}

Xaml

Now in the xaml we can simply bind to the View Models properties directly without any fuss.

<Window x:Class="SO_WPF.MainWindow"
        xmlns:viewModels="clr-namespace:SO_WPF.ViewModels"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        d:DataContext="{d:DesignInstance {x:Type viewModels:MainVM}}"
        Title="MainWindow"
        Height="300"
        Width="400">

<StackPanel Orientation="Vertical">
    <ListBox Name="lbData"
                ItemsSource="{Binding Members}"
                SelectionMode="Multiple"
                Margin="10" />

    <Button Height="30"
            Width="80"
            Margin="10"
            Content="Click Me" />
</StackPanel>

</Window>

In the above code we bind the Members to the listbox just by specifying the Members property name. As to the highlighted lines, I have added them as a debug design option. That lets Visual Studio and Blend know that our data context is our MainVM. That allows for the editor to present us with the options of data binding to the appropriate items, and not having it blank.

This has been a simple example, but a powerful one which can be used as a binding strategy for any WPF, Silverlight or Windows Phone Xaml based applications in C#.

Note though it is not shown, sometimes in styles one needs the element name to bind to, where the data context will fail due to the nature of the style binding, the above page we would bind to the page name as provided (“MainWindow”) and then the property name as usual!

Extra Credit ICommanding

I won’t go into much detail about commanding, but the gist is that the ViewModel is not directly responsible for actions which can happen due to the ICommanding process, but allow for binding operations to occur against those actions and those actions are performed elsewhere usually on a view.

Below is our view model with the commanding public variables which can be consumed by controls (or other classes which have access to the VM).

public class MainVM : INotifyPropertyChanged
{
    #region Variables
       #region Commanding Operations

    public ICommand ToggleEditing { get; set; }
    public ICommand ReportError   { get; set; }
    public ICommand CheckSequence { get; set; }

       #endregion
       #region Properties
    public string ErrorMessage { // the usual INotifyProperty as shown before }
       #endregion
    #endregion
}

Then on our main page which consumes the view model we then process those requests by creating methods to fulfill those operations. Note that the example below references properties on the VM which were not shown in the example,
but that is not important in this article. But one variable is shown and that is the error message. This allow anyone to push an error using the commanding to the viewmodel which is subsequently shown. That is a peek at the power of commanding right there to allow a dependency injection of setting an error variable to be done outside the VM but used by those which consume the VM!

public partial class MainWindow : Window
{

    public MainWindow()
    {
        InitializeComponent();

        // Set the windows data context so all controls can have it.
        DataContext = ViewModel = new MainVM();

        SetupCommanding();
    }

    private void SetupCommanding()
    {
        // Commanding using OperationCommand class
        ViewModel.ToggleEditing         = new OperationCommand((o) => ViewModel.IsEditing = !ViewModel.IsEditing);
        ViewModel.ReportError           = new OperationCommand((o) => ViewModel.ErrorMessage = (string)o);
        ViewModel.CheckSequence         = new OperationCommand(CheckSequences, CanExecute);

    }

     private void CheckSequences(object obj)
     {
        ...
     }

    private bool CanExecute(object obj)
    {
        return !ViewModel.UnsavedsExist;
    }
}

Finally the ICommanding class used.

public class OperationCommand : ICommand
{

    #region Variables

    Func<object, bool> canExecute;
    Action<object> executeAction;

    public event EventHandler CanExecuteChanged;

    #endregion

    #region Properties

    #endregion

    #region Construction/Initialization

    public OperationCommand(Action<object> executeAction)
        : this(executeAction, null)
    {
    }

    public OperationCommand(Action<object> executeAction, Func<object, bool> canExecute)
    {
        if (executeAction == null)
        {
            throw new ArgumentNullException("Execute Action was null for ICommanding Operation.");
        }
        this.executeAction = executeAction;
        this.canExecute = canExecute;
    }

    #endregion

    #region Methods

    public bool CanExecute(object parameter)
    {
        bool result = true;
        Func<object, bool> canExecuteHandler = this.canExecute;
        if (canExecuteHandler != null)
        {
            result = canExecuteHandler(parameter);
        }

        return result;
    }

    public void RaiseCanExecuteChanged()
    {
        EventHandler handler = this.CanExecuteChanged;
        if (handler != null)
        {
            handler(this, new EventArgs());
        }
    }

    public void Execute(object parameter)
    {
        this.executeAction(parameter);
    }

    #endregion
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Xaml: Call Binding Converter Without Defining StaticResource in Xaml Thanks to Markup Derived Base Class in C#

When developing Xaml everyone has to create a converter in code at some point for binding data conversion. Of course to expose that converter to the Xaml bindings one has to specify it in as a static instantiated resource to be available to the binding call(s). In this post I demonstrate how to remove the middle man of that Xaml static instantiation to reside in a common base class which can be derived by the existing converters with minimal change. Once that is in place the converter will also be a MarkupExtension which can be called directly within the { } brackets such as shown on the highlighted line:

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:converters="clr-namespace:Omega.Operation.Converters"
        ...
        >

<DataGrid Grid.Row="1"
          Visibility="{Binding IsEditing, 
                       Converter={ converters:BooleanToVisibilityReverseConverter } 
                      }">
Convert the Converter

The change to any converter is quite minimal and once the base class (shown later) is in place it is simply a one line change. Here is the code for the converter used above.

The highlighted line shows the change;  simply adding the base class to its definition with a generic template of itself:

namespace Omega.Operation.Converters
{
/// <summary>Does the reverse where if a value is true the control is collapsed and if false the control is visibile</summary>
public class BooleanToVisibilityReverseConverter : CoverterBase<BooleanToVisibilityReverseConverter>, 
                                                   System.Windows.Data.IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return (value is bool && (bool)value) ? Visibility.Collapsed : Visibility.Visible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value is Visibility && (Visibility)value == Visibility.Collapsed;
    }
}
}
Base Class Magic

The following generic base class will instantiate the derived class and return a single static instance of the derived class for usage in Xaml:

/// <summary>
/// This creates a Xaml markup which can allow converters (which inheirit form this class) to be called directly
/// without specify a static resource in the xaml markup.
/// </summary>
public  class CoverterBase<T> : MarkupExtension where T : class, new()
 {
    private static T _converter = null;

    public CoverterBase() { }

    /// <summary>Create and return the static implementation of the derived converter for usage in Xaml.</summary>
    /// <returns>The static derived converter</returns>
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return _converter ?? (_converter = (T) Activator.CreateInstance(typeof (T), null));
    }
}

With the base class providing the required implementation of for the MarkupExtension, the derived class can be simply called in the Xaml and avoiding having to use the static resource implementation.

Things to Consider
  • Works in WPF, Silverlight, Windows Phone 8 (WP8), and Windows 8 Store apps.
  • Visual Studio’s Xaml designer may give blue squiggly warning “No constructor type for ‘xxx’ has 0 parameters.”. Ignore that warning…for there is a default constructor which doesn’t have to be defined in C#.
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C# Regex for Parsing Known texts

A user wanted to parse basic text. Here is a regex pattern which  breaks out the user text.

 

string @pattern = @"
(?:OS\s)                     # Match but don't capture (MDC) OS, used an an anchor
(?<Version>\d\.\d+)          # Version of OS
(?:;)                        # MDC ;
(?<Phone>[^;]+)              # Get phone name up to ;
(?:;)                        # MDC ;
(?<Type>[^;]+)               # Get phone type up to ;
(?:;)                        # MDC ;
(?<Major>\d\.\d+)            # Major version
(?:;)
(?<Minor>\d+)                # Minor Version
";

string data = 
@"Windows Phone Search (Windows Phone OS 7.10;Acer;Allegro;7.10;8860)
Windows Phone Search (Windows Phone OS 7.10;HTC;7 Mozart T8698;7.10;7713)
Windows Phone Search (Windows Phone OS 7.10;HTC;Radar C110e;7.10;7720)";

 // Ignore pattern white space allows us to comment the pattern, it is not a regex processing command
var phones = Regex.Matches(data, pattern, RegexOptions.IgnorePatternWhitespace)
                  .OfType<Match>()
                  .Select (mt => new 
                  {
                    Name = mt.Groups["Phone"].Value.ToString(),
                    Type = mt.Groups["Type"].Value.ToString(),
                    Version = string.Format( "{0}.{1}", mt.Groups["Major"].Value.ToString(),
                                                        mt.Groups["Minor"].Value.ToString())
                  }
                  );
                  
Console.WriteLine ("Phones Supported are:");            

phones.Select(ph => string.Format("{0} of type {1} version ({2})", ph.Name, ph.Type, ph.Version))
      .ToList()
      .ForEach(Console.WriteLine);
      
/* Output
Phones Supported are:
Acer of type Allegro version (7.10.8860)
HTC of type 7 Mozart T8698 version (7.10.7713)
HTC of type Radar C110e version (7.10.7720)
*/
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C#: Combine Two Values Together From a List Into Pairs

Sometimes in C# .Net (see Notes section on usage for before .Net 4)  one might have a list of items and want to make them into pairs. Possibly to take those pairs and place the them into a dictionary. If the items are in a list, that list is linear by nature and using linq is not an option when using the extension ToDictionary.

I have created extension methods to create paired values from any list and those methods are named AsPairs and AsPairsSafe. If the list is odd in length, the final number will be combined with the system default for that type as handled in the method AsPairs. If that is not desired then call AsPairsSafe which will skip the last odd value.

Here is the usage of the AsPairs extension on integers and strings:

var ints = new List<int> { 1, 2, 3, 4, 5 };

IEnumerable<Tuple<int,int>> asTuplePairs = ints.AsPairs();

/* asTuplePairs looks like this(Note value 5 is paired with a default value of 0)
1,2 
3,4
5,0
*/

var strings = new List<string> { "Alpha", "Beta", "Gamma", "Delta", "Omega" };

IEnumerable<Tuple<string,string>> asTuplePairsStrings = strings.AsPairs();

/* asTuplePairsStrings (note Omega is paired a default value of Null)
Alpha, Beta 
Gamma, Delta
Omega, NULL

Whereas the call to AsPairsSafe would return without Omega:
Alpha, Beta 
Gamma, Delta
*/

Here are the extension methods:

public static class MyExtensions
{
   // Create Pairs from a list. If the list is odd add a default value for the final pair. 
   public static IEnumerable<Tuple<T, T>> AsPairs<T>(this List<T> list)
   {
      int index = 0;

      while (index < list.Count())
      {
         if (index + 1 > list.Count())
            yield break;

         if (index + 1 == list.Count())    
            yield return new Tuple<T,T>(list[index++],  default(T));
         else
            yield return new Tuple<T,T>(list[index++],  list[index++]);
      }
   }

   // Create Pairs from a list. Note if the list is not even in count, the last value is skipped.
   public static IEnumerable<Tuple<T, T>> AsPairsSafe<T>(this List<T> list)
   {
      int index = 0;

      while (index < list.Count())
      {
         if (index + 1 >= list.Count())
            yield break;

         yield return new Tuple<T,T>(list[index++],  list[index++]);
      }

   }
}

Notes

Tuple is a .Net 4 item. If you are using a previous version of .Net use the KeyValuePair structure instead.

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C# Silverlight WCF: Thread Safe Multiple Async Call Strategy With Final Operation To Join Data.

Seven Pointing Arrows ending at different points except one arror leaping of the page to show the final Async call.This article describes one way to handle asynchronous or async calls in .Net 3.5 or .Net 4.0 when using WCF in Silverlight in C#. The goal is to have a final operation wait for all the calls to finish so to combine all the data gathered, all in a thread safe way. A secondary goal is to minimize the consumer code required to perform this operation from what is currently available in straight WCF async calls.

This article has a short shelf life because after .Net 4 (see What’s Next in C#? Get Ready for Async!) one will use the built in Asynchrony methodology developed. Until that time if one is using any version of Silverlight and WCF then this article describes how to handle those multiple async calls and join the data in a final method call.

Final Result Example

Before delving into the solution, here is how the consumer will use the methodology. Below a user is getting account information of user requests, departments and accounts to join all the data on the view model in the final method for display on a Silverlight page. Thesee operations as shown are setup when the view model class (MyViewModel) is created and no blocking occurs keeping UI thread clear.

public MyViewModel()
{
    DataContext = new MyServiceClient();

    FinalAsync(CombineDataAndDisplay); // When all the data is retrieved, do this method to combine the data From the 3 async callls below

    // Provide the operation as a lambda (could be a method call) to assign data to our target backing store property
    // and if all has gone well (no errors in other async calls) and it is the final completing operation. Do the final
    // Processing call automatically.
    DataContext.GetUserRequestsCompleted   += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _UserRequests, "Acquisition failure for User Requests");};
    DataContext.GetAccountsCompleted       += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Accounts, "Acquisition Failure for Accounts"); };
    DataContext.GetDepartments             += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Departments, "Failed to get Department Info."); };   

    // Start the Async processes 
    MultipleAsyncRun(DataContext.GetUserRequestsAsync);
    MultipleAsyncRun(DataContext.GetAccountsAsync);
    MultipleAsyncRun(DataContext.GetDepartmentsAsync);

    // Exit out and return the UI thread to the user operations.
}

// Once all the data is done, combine and assign into our
// PagedCollectionView property for display on the screen.
public void CombineDataAndDisplay()
{
    // Combine missing data on the calls
   _UserRequests.ToList()
                .ForEach(ur =>
                {
                ur.BillingName     = _Accounts.First(ac => ur.AccountID == ac.AccountID).Name;
                ur.DepartmentName  = _Departments.First(dp => dp.DepartmentID == ur.DepartmentID).Name;
                });


    UserRequests = new PagedCollectionView( _UserRequests);
    UserRequests.GroupDescriptions.Add(new PropertyGroupDescription("DepartmentName"));

}
Explanation
Line  5: The final async call is where this process specifies a method to use after all async calls are completed. On line 24 of the example is our final operation method to do that which is reported to FinalAsync.
Line 11-13: Just like the normal async process we subscribe to the anync handler but we handle it in a anonymous lambda.
Line 11-13: AssignResultCheckForAllAsyncsDone method will check the result returned, code show later in the article. All one needs to know now is that the respective _UserRequests, _Accounts and _Departments, all backing store variables (not properties) will be loaded with the data if the result information ( e ) operation contains no errors. This method does all the heavy lifiting by checking error state, loading the data variable, decrementing the async count and firing off the final method if all asynchronous operations are completed.
Line 16-18: Just like the normal WCF async process we must launch the asnc calls and these statements do just that. We supply the method to be launched inside the MulipleAsync method.
Line 24: Here is our final method to be executed once the asynchrony process is complete. This method combines all the async data internally into the _UserRequest object at which it becomes complete and can be used.
Line 34: Finally a paged collection view is created from our data to be bound to Silverlight Xaml items which is our end result.
24-37: Note: The section below has a variable entitled AsyncErrors. The above example did not check that for null or an error situation. I have left out the check of AsyncErrors for brevity of the example. See the last section for an example of proper error handling.

Multiple Async Methodology Plumbing

Below is what will needed to be brought into your View Model, or placed on your page if not using MVVM. This is where the .Net thread safe Silverlight asynchronous operations will occur.

// Lock Objects 0 for false, 1 for true.
private int AsyncErrorResource = 0;
private int AsyncFinal = 0;

private List<Exception> AsyncErrors;  // If not null errors have been encountered.

private int PendingAsyncOperations; // Holds the counted total of ongoing async operations. Zero means do users final operation.

private Action FinalOperation;      // The user's final operation.

public void MultipleAsyncRun(Action Operation)
{
    Interlocked.Increment(ref PendingAsyncOperations);
    Operation();
}

public void FinalAsync(Action method)
{
    FinalOperation = method;
}

public void AssignResultCheckforAllAsyncsDone<T>(AsyncCompletedEventArgs ea, T receivedData, ref T assignTo, string ErrorMessage)
   where T : class
{
    bool valid = !((ea.Error != null) || (receivedData == null));

    if (valid == false)
    {
        if (0 == Interlocked.Exchange(ref AsyncErrorResource, 1))
        {
            if (AsyncErrors == null)
                AsyncErrors = new List<Exception>();

            AsyncErrors.Add(ea.Error);

            //Release the lock
            Interlocked.Exchange(ref AsyncErrorResource, 0);
        }
    }
    else
    {
        assignTo = receivedData;
    }

    Interlocked.Decrement(ref PendingAsyncOperations);
    if (PendingAsyncOperations == 0)
    {
        if (0 == Interlocked.Exchange(ref AsyncFinal, 1))
        {
            FinalOperation();
        }

        Interlocked.Exchange(ref AsyncFinal, 0);
        Interlocked.Decrement(ref PendingAsyncOperations); // Move to -1
    }
}
Explanation
Line  2/3: These variables are used as a lock targets for thread safety. Value zero means its open and a value of 1 means a lock is in place.
Line  5: Any errors encountered are placed into AsyncErrors. The final operation must check this variable. If it is not null errors have occurred and data is incomplete see the final section of this article on how to handle errors.
Line 7: This variable will hold the running total async operations. Once it gets to zero the final operation will be executed.
Line 11: This method counts and stores our async operations as they come in and launches the async method as well.
Line 13: This process uses the Interlocked class found in the System.Threading namespace. To quote Microsoft, “Provides atomic operations for variables that are shared by multiple threads. “. We simply count up the PendingAsyncOperations variable. Later when the operations complete this will be decremented.
Line 18: This method is called by the consumer so we know what method to launch when all async operations have completed. We assign the method to a holder variable as found on line 9.
Line 22: This method will take in the event arguments and check if there is a problem. It will store the error if there is one and also decrement our count. If our count hits zero it will launch the users final operation.
25-39: Checking errors reported by the async call. If there are any we log them and do not assign the variable. Note whether an error exists or not the operation continues below where the final operation is checked for and executed. Its up to the final operation to check if errors exists and handle them appropriately.
Line 42: If the event reports a success this is where we assign the value to the passed in reference to the template T assignTo. If one doesn’t use a variable for assignTo reference an exception will be generated on this line. See the following section as to why. 
Line 46: We safely decrement our operations count variable. Zero means we are done!
Line 47-57: Here is where we execute the final operation when the count is zero. Note there is an extra lock if operations unlikely hit a zero at the same time. The extra lock ensures only one will execute the final method.

That is it, simply use the above code and you can have all your operations work done asynchronously. Smile Now for the disclaimers…

Why Can’t Properties be Used by AssignResultCheckforAllAsyncsDone?

We must use direct variables like in our example

private ObservableCollection<UserRequestDTO> _UserRequests;
private ObservableCollection<Account> _Accounts;
private ObservableCollection<Department> _Deparments;

// Not Private ObservableCollection<Department> _Departments { get; set; }

If one used a property this exception is thrown.

A property, indexer or dynamic member access may not be passed as an out or ref parameter

That is because we are using the generic method AssignResultCheckforAllAsyncsDone to assign a value, and that assignment has to have an exact object instance for the template (T) object and not a Property to assign the value. If your end result is in a property, simply assign it from the variable to the property in the final async call.

Handling Errors

Simply check the error variable if it is not null it has encountered errors.

if (AsyncErrors != null)
{
    MessageBox.Show("Errors: " + string.Join(string.Format("{0}{0}", Environment.NewLine), AsyncErrors.Select(ex => ex.Message)));
}
else
{
    // Success Handle accordingly.
}
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C#: How to Load a Winform ComboBox or ListBox and have a Unique Value Associated with the Selected Item

ComboListBox When loading a list box or a combo box drop down in a Winform most developers can use the Items property of the Add method to get the individual textual items to be chosen. The problem comes in later when the developer needs to get certain information beyond the text of the item itself. They need to tag a value to the item, so that future processing can commence. (See my post C# Winforms and the Hidden Association Tag for more information on how to load those types of controls.)

That item to be associated could be an integer, a string or even an actual object. This article demonstrates how do that by loading a KeyValuePair object (or a Tuple for .Net 4) into the box where the display text will be shown but it will also carry a payload to allow us to process things in the future.

Loading ComboBox and ListBox

The following code shows how to load the boxes. The goal is to have Alpha, Beta and Gamma as the selectable text and the payload values they will carry to be 5, 6 and 7 respectfully. Here is the code to load.

List<string> displayValues = new List<string>() { "Alpha", "Beta", "Gamma" };

var dict = displayValues.Select( ( item, index ) => new KeyValuePair<string, string>( item, ( index + 5 ).ToString() ) );

cbOne.DisplayMember =
lbOne.DisplayMember = "Key";

// Convert the objects to array and the controls
// will extract the appropriate values to display
// and use for a value.
cbOne.Items.AddRange( dict.OfType<object>().ToArray());
lbOne.Items.AddRange( dict.OfType<object>().ToArray());

Explanation

Line 1: Contains our list items to show to the user.

Line 3: Thanks to Linq we enumerate the displayValues list and on each indexed item we add 5 to the that index value. That creates key value pairs of (“Alpha”, (0+5)), (“Beta”, (1 + 5)), (“Gamma”, (2+5)). Note one doesn’t have to use a string as a value it could be a whole new instance of a class.

Line 5-6: We inform the combobox and the listbox that when it processes and creates the items, use “Key” for the display text for the user.

Line 11-12 : We load our combo box an list box accordingly. Note how we have to change the type of the item return to be an array of objects thanks to the OfType<object>() extension. This is done because the boxes take objects and not a specific object. It allows us a greater flexibility.

That loads our controls. Build and run to see the controls with the selected values.

Value Extraction

Now we have a button on the screen which when clicked gets the current item and extracts our value data to use. It takes those values and displays them to labels next to the target controls so we can see it working. Here is the code

private void btShowSelectedValues_Click( object sender, EventArgs e )
{
    label1.Text = string.Format( "Value: {0}", ((KeyValuePair<string,string>)lbOne.SelectedItem).Value );
    label2.Text = string.Format( "Value: {0}", ((KeyValuePair<string, string>)cbOne.SelectedItem ).Value );

}

What is happening is that we get the target selected items and cast them to the key value pair object. Once that is done we can extract the actual value, string in this case and write it to the display. Its that simple.

A Larger Trojan Horse

Ok you say, the example is great and you understand that instead of a string for the Value, you could use a class. But what if you need to have more than one value? If you are using .Net 4 use a Tuple. Here is the same code but with a Tuple<>  and three separate objects used instead. Two of the objects will be another class and an enum.

public class OtherClass
{
    public string Action { get; set; }
}

public enum OpValue
{
    Condor,
    Eagle,
    Hawk
}

Here is how we load our boxes and setup the Tuple:

List<Tuple<string, OtherClass, OpValue>> myList = new List<Tuple<string, OtherClass, OpValue>>()
{
    { new Tuple<string, OtherClass, OpValue>( "Alpha", new OtherClass() { Action="Max" }, OpValue.Condor )},
    { new Tuple<string, OtherClass, OpValue>( "Beta", new OtherClass()  { Action="Move" }, OpValue.Hawk )},
    { new Tuple<string, OtherClass, OpValue>( "Gamma", new OtherClass() { Action="Reset" }, OpValue.Eagle)}
};

cbOne.DisplayMember =
lbOne.DisplayMember = "Item1";

// Convert the objects to array and the controls
// will extract the appropriate values to display
// and use for a value.
cbOne.Items.AddRange( myList.OfType<object>().ToArray() );
lbOne.Items.AddRange( myList.OfType<object>().ToArray() );

Here is the button click which will extract our tuple and use the the Action property of our class. Once we have the tuple casted we could use anything…but you know that.

private void btShowSelectedValues_Click( object sender, EventArgs e )
{
    label1.Text = string.Format( "Value: {0}", ( (Tuple<string, OtherClass, OpValue>)lbOne.SelectedItem ).Item2.Action );
    label2.Text = string.Format( "Value: {0}", ( (Tuple<string, OtherClass, OpValue>)cbOne.SelectedItem ).Item2.Action );
}

Here is the final output when run:

Tuple

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