Silverlight and WCF

31 05 2008

With the release of Silverlight 2 beta 1, now developers can use .Net to create Silverlight applications To be more precise, developers can use XAML and VB.NET or C# as the back-end code language. To know more about Silverlight and what tools you need to start developing Silverlight applications, visit my post here.

This post focuses on how to make your Silverlight applications interact with Windows Communication Foundation(WCF) services. Visual Studio 2008 introduced several new WCF features. We will create a small calculator service which is going to add two numbers and return the result to the user.

First, let us create a Silverlight Web Application project.

silverlight-project

Visual Studio creates the necessary files needed for your solution. Let us straight away start with adding our WCF service. Visual Studio creates two projects, one being the actual Silverlight control project and the other being the web application project where the Silverlight control is hosted. So, we would be able to add a WCF service to our web application project and then reference the service in our Silverlight control project. Right click the web application project and add a WCF service to the project.

add-new-item

Name the service as CalculatorService. Visual Studio adds the necessary files such as the SVC and code-behind files and also the service configuration to the web.config file.

wcf-service-added

I have modified the service to hold only function as shown below:

[ServiceContract]
public interface ICalculatorService
{
    [OperationContract]
    int AddTwoNumbers(int num1,int num2);
}

And here is the implementation:

#region ICalculatorService Members

public int AddTwoNumbers(int num1, int num2)
{
    return (num1 + num2);
}

#endregion

Nothing complex, just simple addition and return the result ;)

Now comes the most important thing, at least for this beta 1 release – Silverlight supports only basicHttpBinding and thus our WCF service can only use basicHttpBinding if we are to interact with a Silverlight client. Let us check our CalcultorService’s binding in the web.config file under the system.servicemodel section.

default-binding

Yes, you are right. WCF by default uses wsHttpBinding and thus we need to change the binding to basicHttpBinding. Below is the modified version:

modified-binding

How do we use this service in our Silverlight application? Below is a screenshot of our Silverlight application.

screenshot-control

The interface is pretty simple accepting two numbers from the user and when Add is clicked, our service’s AddTwoNumbers is invoked to get the result.

How do we reference our WCF service now? We do the same way as we do in normal WPF or WinForms applications :D

Right click on the Reference and select Add Service Reference

silverlight-add-service-reference

We will be presented with a dialog box to add a service reference.

service-discover

We can use the Discover option to discover any WCF services in our solution. As our CalculatorService is hosted in the same solution, the Discover would be able to find our service.

calculator-service-discovered

Let us give a name to our service reference – CalculatorServiceProxy :)

Once we add our service, we can see that the Silverlight project now has the necessary files to interact with our WCF service.

silverlight-added-wcf-reference-files

Now we are ready to add our code to the button Click event handler. Below is the code snippet.

private void Button_Click(object sender, RoutedEventArgs e)
{
    int num1 = Convert.ToInt32(TxtNum1.Text);
    int num2 = Convert.ToInt32(TxtNum2.Text);

    CalculatorServiceClient calculator_proxy =
        new CalculatorServiceClient();

    calculator_proxy.AddTwoNumbersCompleted +=
        new EventHandler<AddTwoNumbersCompletedEventArgs>
            (calculator_proxy_AddTwoNumbersCompleted);

    calculator_proxy.AddTwoNumbersAsync(num1, num2);

}

void calculator_proxy_AddTwoNumbersCompleted(object sender,
    AddTwoNumbersCompletedEventArgs e)
{
    HtmlPage.Window.Alert(Convert.ToString(e.Result));
}

You guessed it right – WCF reference adds the asynchronous operations to our Silverlight project and it does makes more sense to use asynchronous operations in a Silverlight environment as we cant block the browser and make the user wait.

Let us build and execute our project :)

And here is the screenshot:

output

That’s it! Now we have a Silverlight application interacting with a WCF service ;)

Wasn’t it easy 8)

The sample can be downloaded here:





Resharper 4.0 – Lambda Support

26 05 2008

Resharper 4.0 beta was out few days back. I found an excellent feature which I think should be blogged :)

Here is small test code snippet which uses RhinoMocks unit testing framework

You can see that Resharper has issued a warning against

Call(delegate { mockSubject.Remove(subject); });

And the warning message is as follows,

You can see that it is intelligent enough to deduce that lambda expressions can be used in the place of anonymous delegates! 8)

And once you allow Resharper to convert to lambda, you get this:

How cool is that 8)





ReSharper 4.0 Beta is out now!

23 05 2008

Resharper 4.0 Beta which supports C# 3.0, LINQ and Visual Studio 2008 is ready for download now! This is THE best addin for Visual Studio and I would recommend it to everyone who uses Visual Studio 8)

Here is an article which compares Plain Visual Studio 2008 Vs Resharper 4.0 Visual Studio 2008

You can download the beta here

Enjoy! :)





C# 3.0 Language Enhancements for LINQ – Part 3 – Expression Trees

14 04 2008

We saw more about Lambda Expression in our Part 1 of this series .Wonder how those were compiled or how those expressions parsed?

To do so, we need to get into Expression Trees!

So what is an Expression Tree?

Expression trees are nothing but those which represent the query itself.

Let us take a simple example.

   1: Func<string, string> function = 
   2:              x => x.Contains("c");

· The compiler constructs a delegate which takes an input parameter of type string and returns a value of type string

But, how about this

   1: Expression<Func<string, string>> expression = 
   2:                             x => x.Contains("c");

· The compiler generates an Expression Tree which we can parse and do something with the data

(This post gives a small introduction to Expression Trees. Expression Trees itself is a big topic but this post will help us go through some of the basics with a simple example)

Say we have a class called Student which has only one property – Name

   1: public class Student
   2: {
   3:     private string name;
   4:  
   5:     public string Name
   6:     {
   7:         get { return name; }
   8:         set { name = value; }
   9:     }
  10: }

And now we have a small function which is going to take an expression as its parameter and return the value for which the expression is queried for.

   1: public static string 
   2:          GetName(Expression<Func<Customer, bool>> predicate)

So, if we pass an expression,

n=>n.Name==”Chakkaradeep”

We need to get back Chakkaradeep , as that’s what we queried. This isn’t a good example, but I would say its good to understand how Expressions are parsed J

Let me show you the function directly now,

   1: public static string GetName(Expression<Func<Student, bool>> predicate)
   2: {
   3:     BinaryExpression binaryExpr = (BinaryExpression)predicate.Body;
   4:  
   5:     MemberExpression leftExpr = (MemberExpression)binaryExpr.Left;
   6:  
   7:     string url = leftExpr.Member.Name;
   8:  
   9:     if (binaryExpr.NodeType == ExpressionType.Equal)
  10:     {
  11:         url += "==";
  12:     }
  13:     else
  14:         throw new NotSupportedException("only = is supported");
  15:  
  16:     ConstantExpression rightValue = (ConstantExpression)binaryExpr.Right;
  17:  
  18:     url += rightValue.Value;
  19:  
  20:     return url;
  21: }

That’s a bit confusing! Whats happening ?

Expression is being parsed :)

Yes, take our expression again,

n=>n.Name==”Chakkaradeep”

Expressions always a Body property. In the above expression, we have a BinaryExpression

n.Name==”Chakkaradeep”

As you might have guessed by now, a BinaryExpression is something that has a binary operator

So lets take the Body and break it into two pieces

image

   1: BinaryExpression binaryExpr = 
   2:       (BinaryExpression)predicate.Body;

Now we have extracted our BinaryExpression body which has a Left property and Right property, as shown above in the diagram.

The Left property will hold n.Name

The Right Property will hold Chakkaradeep

And our Node Type or the Binary operator is == (Equality)

And that’s what we have done,

   1: string url = leftExpr.Member.Name;
   2:  
   3: if (binaryExpr.NodeType == ExpressionType.Equal)
   4: {
   5:     url += "==";
   6: }
   7: else
   8:     throw new NotSupportedException("only = is supported");
   9:  
  10: ConstantExpression rightValue = (ConstantExpression)binaryExpr.Left;
  11:  
  12: url += rightValue.Value;

As now you have the values, you could do anything with them and parse them :)

But yes, it would be more complicated if we have multiple queries coming up, like,

n=>n.Name==”Chakkaradeep” && n.Name==”Chaks”

And our sample will not work for the above query as we havent dealt with it. I leave to the reader to explore more on how to recursively parse Expressions :)

What if we need to manually build Expressions?

You can :)

We just use the technique of how we parsed to build the expression manually.

First, we need to create a ParameterExpression of type Student and also tell that our paramter variable is x

   1: //construct the parameter which is x and it is of type Student
   2: ParameterExpression xParam = 
   3:   Expression.Parameter(typeof(Student), "x");

And now we need to build our BinaryExpression whose Left Property is a MemberExpression which has the Property Name and the Right Property a value

   1: //construct our MemberExpression whose
   2: //left property is x.Name, and
   3: //right property’s value "Chakkaradeep"
   4: Student student = new Student();
   5: student.Name = "Chakkaradeep";
   6: MemberExpression leftExpr = MemberExpression.Property(xParam, "Name");
   7: Expression rightExpr = Expression.Constant(student.Name);
   8: //construct our BinaryExpression which is x.Name=="Chakkaradeep"
   9: BinaryExpression myExpr = MemberExpression.Equal(leftExpr, rightExpr);

All good now to build our Expression. Remember, we haven’t yet built our Expression, but we do have the bits and pieces that we need to build our expression 

image

And now we build our Expression,

   1: //now build our Expression using the parameter and BinaryExpression
   2: //x=>x.Name=="Chakkaradeep"
   3: Expression<Func<Student, bool>> lambdaExpr =
   4:     Expression.Lambda<Func<Student, bool>>
   5:         (
   6:             myExpr,
   7:             new ParameterExpression[] { xParam }
   8:         );

There you go! We build it telling that we have a ParameterExpression of type Student and the parameter is x which is associated with the BinaryExpression

And now you can directly pass this lambdaExpr to our function

GetName(lambdaExpr);

You can download the sample here

Useful Resources

1) Expression Trees

2) Expression Tree Visitor

3) System.Linq.Expressions Namespace





C# 3.0 Language Enhancements for LINQ – Part 2 – var Keyword, Extension Methods and Partial Methods

13 04 2008

The var Keyword

We come across this new keyword called var when we use LINQ, what does this var keyword do?

The var keyword is used to declare and initialize anonymous types

That’s really confusing! – What are these anonymous types?

To understand the var keyword, we need to understand what really anonymous types are, and to understand anonymous types we need to know about var keyword, lol! Both go hand in hand.

Let’s start with an example,

   1: var Student = new { Id = 1234, Name = "Chakkaradeep" };

Now we have an anonymous type which has the properties Id and Name declared and initialized using the var keyword. To illustrate what is happening here,

image

So we can come to a conclusion that the var keyword deduces the data type of an object with the initialization of that object.

Now you can do something like this,

   1: var query =
   2:       from name in names
   3:       select new
   4:       {
   5:             firstPart = name[0],
   6:             lastPart = name.Substring(1, (name.Length - 1))
   7:       };

And then used it this way,

image

But do not consider that var variable is loosely coupled and can change its type! Take an example,

   1: var FullName = "Chakkaradeep Chandran";
   2: FullName = 12;

When you compile the above code, it fails because the object FullName is initialized as a String and we are trying to assign an Integer value to it!

This brings up an important point – var variables must be initialized when they are being declared and that helps the var keyword to deduce its type

The introduction of anonymous types has also led to another change in the way objects and collections are initialized

Say, we have a Class Person

   1: public class Person
   2: {
   3:     public string Name;
   4:     public string Address;
   5:     public int Pincode;
   6: }

If you want to initialize an object of type Person and give default values to those properties, the normal way would be,

   1: Person person = new Person();
   2: person.Name = "Chakkaradeep";
   3: person.Address = "Dunedin";
   4: person.Pincode = 9016;

But now we could directly do this,

   1: Person person = new Person
   2: {
   3:     Name = "Chakkaradeep",
   4:     Address = "Dunedin",
   5:     Pincode = 9016
   6: };

That certainly looks easier and neat!

This doesn’t stop with only Classes; it’s even possible with Collections,

   1: List<string> persons = new List<string>
   2: {
   3:     "Wellington",
   4:     "Dunedin",
   5:     "Invercargill"
   6: };

Extension Methods

The best way to understand Extension Methods is from an example

Let’s take our previous post’s example of filtering names that contains a character. We did something like this,

   1: List<string> FilteredNames =
Utility.FilterNames(names, n => n.Contains('c'));

Wouldn’t it be really nice and useful to provide something like this?

   1: List<string> FilteredNames =
   2:       names.Filter(n => n.Contains('c'));

That’s what Extension Methods allows us to do!

What are we actually doing in our above code block?

- We have “added” a method called Filter to an existing type which is string[] (array of strings)

This has one advantage. It doesn’t require you modify anything in the type string[], we just extend it and add our method

So, how are these done?

Extension Methods are nothing but static methods in a static class that can be called by using instance method syntax

We need to do some changes to our Utilty class to make it ready for Extension Methods. We need to change the class to a static class and include a static method called Filter

   1: namespace LINQEnhancements
   2: {
   3:     public static class Utility
   4:     {
   5:         public static List<string>
   6:            Filter(this string[] names,
   7:                 Func<string, bool> customFilter)
   8:         {
   9:             List<string> NamesList = new List<string>();
  10:
  11:             foreach (string name in names)
  12:             {
  13:                 if (customFilter(name))
  14:                     NamesList.Add(name);
  15:             }
  16:
  17:             return NamesList;
  18:         }
  19:     }
  20: }

And now you can use the way we want it,

   1: List<string> FilteredNames;
   2: FilteredNames = names.Filter(n => n.Contains('c'));

The reason I have shown the Utility class along with namespace is that, if your extension methods are in a different namespace, you have to import that namespace to actually make use of those extension methods

   1: public static List<string>
   2:   Filter(this string[] names,
   3:       Func<string, bool> customFilter)

The above line is where our trick lies. We explicitly tell that Filter is a static method applied on a static variable of type string[] (array of strings)

Where are these used? Remember our Standard Query Operators in LINQ?

   1: IEnumerable<string> query = names
   2:                             .Where(n => n.Equals(matchName))
   3:                             .Select();

Yes, you got it right!

And all these Standard Query Operators are available to use by importing the namespace System.Linq

using System.Linq;

Partial Methods

A partial method has its signature defined in a partial type and its implementation defined in another part of the type. This sounds very similar to Partial Class. Yes, partial methods always reside inside partial classes so that they can be used in another part of the type.

Here is an example,

   1: public partial class MyPartialClass
   2: {
   3:     partial void MyPartialMethod();
   4:
   5:     public void NotPartial()
   6:     {
   7:         Console.WriteLine("Ooops..Not Partial!");
   8:     }
   9:
  10:     public void InvokePartialMethod()
  11:     {
  12:         MyPartialMethod();
  13:     }
  14: }

We have a partial class and a partial method called MyPartialMethod

Now, what happens if we do something like this?

   1: MyPartialClass partialClass = new MyPartialClass();
   2: partialClass.NotPartial();
   3: partialClass.InvokePartialMethod();

We do see that the method NotPartial gets invoked but nothing happens when we call the InvokePartialMethod

Now let us create another declaration for MyPartialClass and implement the partial method MyPartialMethod

   1: partial class MyPartialClass
   2: {
   3:     partial void MyPartialMethod()
   4:     {
   5:         Console.WriteLine("Hey, its a Partial Method!");
   6:     }
   7: }

And now do the same thing,

   1: MyPartialClass partialClass = new MyPartialClass();
   2: partialClass.NotPartial();
   3: partialClass.InvokePartialMethod();

We now see that our partial method too gets called as we have implemented it!

Well, there is lot of arguments going on in the community that why do we need Partial Methods when this can be achieved in many other ways. Partial methods are mostly used in design tools for use with auto-generated code. If you want to make use of those methods, you could write your own implementation and it’s going to be used, else the compiler just doesn’t execute them and moves on.

Partial Methods are heavily used by LINQ-to-SQL designer tools and that’s the reason I wanted to explain about them here.

There are some golden rules that we need to follow if we are writing partial methods,

· Partial method declarations must begin with the contextual keyword partial and the method must return void.

· Partial methods can have ref but not out parameters.

· Partial methods are implicitly private, and therefore they cannot be virtual.

· Partial methods cannot be extern, because the presence of the body determines whether they are defining or implementing.

· Partial methods can have static and unsafe modifiers.

· Partial methods can be generic. Constraints are put on the defining partial method declaration, and may optionally be repeated on the implementing one. Parameter and type parameter names do not have to be the same in the implementing declaration as in the defining one.

· You cannot make a delegate to a partial method.

Useful Resources

1) Standard Query Operators

2) LINQ-to-SQL





C# 3.0 Language Enhancements for LINQ – Part 1

10 04 2008

LINQ is a new feature added to C# 3.0. For an introduction to LINQ, please visit here

So, how are we able to use LINQ seamlessly with C#? Thanks to some of the enhancements that were made to C# for LINQ. They are as follows,

1) Lambda Expressions

2) The var Keyword

3) Extension Methods

4) Partial Methods

5) Expression Trees

This is the start of 3 part series which would be,

· Part 1 – Lambda Expressions

· Part 2 – The var Keyword, Extension Methods and Partial Methods

· Part 3 – Expression Trees

As said above, this post will be explaining about Lambda Expressions

Lambda Expressions

Lambda Expression is an anonymous function that can contain an expression or statement or can also be used to create a delegate.

To understand Lambda Expressions, it is better to first look into,

1) Named Methods

2) Anonymous Methods

Named Methods

With delegates one can create Named Methods, that is, instantiate a named method to a delegate and invoke it

image

Nothing gets explained better without an example; so, let’s get into our sample application

Sample Application

We are going to create a sample application which is going to filter names that contains a character. It’s a very basic and simple example, but it’s really good to explain the things that we want to explore. We would be seeing on how we approach the same concept using Named Methods and Anonymous Methods and then come to Lambda Expressions.

We have a small class called Utility which looks like this,

clip_image004

It has got two static methods and a delegate called CustomFilter with an input parameter as string and bool as return type. So, the idea is to allow the developer or user to write their own custom filter function, but use this Utility to filter. This is done with the help of delegates.

Using Named Methods

So, if we take our Named Method approach, we would end up doing like this,

static void UsingNamedMethods()

{

List<string> FilteredNames =

Utility.FilterNames(names, MyFilter);

foreach (string name in FilteredNames)

Console.WriteLine(name);

}

static bool MyFilter(string name)

{

if (name.Contains(‘c’))

return true;

return false;

}

We have a method called MyFilter which is where we define our custom filter logic and instantiate the delegate CustomFilter with this method using the Utility.FilterNames function

And here is our Utility.FilterNames function

public delegate bool CustomFilter(string name);

public static List<string>

FilterNames(string[] names,CustomFilter customFilter)

{

List<string> NamesList = new List<string>();

foreach(string name in names)

{

if (customFilter(name))

NamesList.Add(name);

}

return NamesList;

}

It’s fairly simple and straight forward. Now we really have something useful which makes use of Named Methods. This sample will help the Customer who is going to use our Utility to write his own Filter and use the generic FilterNames function to filter it.

Look into our filter method which is Myfilter – It’s fairly simple, just checking whether the name contains a character and returns true if so. Do we really need to write a method for this? Why can’t we specify a code block instead and make use of it? Anonymous Methods comes to our rescue!

Anonymous Methods

Anonymous methods can be used to pass a code block to a delegate, using the delegate parameter, and can be used in places where creating a method is really not necessary, like in our example.

Using the Anonymous method, our code changes to,

static void UsingAnonymousMethods()

{

List<string> FilteredNames;

FilteredNames =

Utility.FilterNames(names,

delegate(string name)

{

return (name.Contains(‘c’));

} );

foreach (string name in FilteredNames)

Console.WriteLine(name);

}

So, now we have a code block which checks for a character in the name and it is passed as our CustomFilter delegate

Note that our FilterNames Utility function remains unchanged.

However, Anonymous methods do have one drawback in regard to readability. It’s more verbose and the code block sometimes becomes really hard to read!

So, do we really have anything which is easy to read and also simple to use? – Yes, and Lambda Expressions comes to our rescue!

Revisiting Lambda Expressions

As I said earlier – Lambda Expression is an anonymous function that can contain an expression or statement or can also be used to create a delegate

The structure of a lambda expression looks like this,

(param1,param2..paramN)=>expression

Basically we have some input parameters delimited with comma on the left and a corresponding expression on the right

The simplest lambda expression is,

x=>x

This is nothing but assigning x to x

Moving forward, our sample’s expression to find a character in the name would now become,

n=>n.Contains(‘c’)

How is the type of ‘n’ inferred? Remember our delegate? Here it is again,

public delegate bool CustomFilter(string name);

If you translate in pure English – Here is a delegate called CustomFilter which accepts one input parameter of type string and returns a value of type bool

So, when we actually make use of lambda expressions, this gets inferred and thus our ‘n’ in the above lambda expression gets inferred that it is of type string and has to return bool. But when inferring types is not possible, you could always do,

(string n)=>n.Contains(‘c’)

This would explicitly specify the type of ‘n’

Coming back to our sample application, now with the use of lambda expressions, we could write,

static void UsingLambdaExpressions()

{

List<string> FilteredNames;

FilteredNames = Utility.FilterNames(names, n => n.Contains(‘c’));

foreach (string name in FilteredNames)

Console.WriteLine(name);

}

Note that our FilterNames Utility function still remains unchanged.

Statement Lambdas

Again, revisiting our lambda expression definition – Lambda Expression is an anonymous function that can contain an expression or statement or can also be used to create a delegate

We did see that lambda expression that has an expression. What about a statement?

Statement lambdas look like,

(param1,param2..paramN)=>{ statement; }

The statement body can contain many statements instead of a single expression. Something like,

FilteredNames =

Utility.FilterNames(

names,

n =>{

bool blnVal;

/*… something here …*/

blnVal = n.Contains(‘c’);

return blnVal;

} );

Lambdas with Func<T,TResult> delegates

Again, revisiting our lambda expression definition – Lambda Expression is an anonymous function that can contain an expression or statement or can also be used to create a delegate

We did see that lambda expression that has an expression, a statement. What about the last one which can be used to create a delegate?

With the Func<T,TResult> family of generic delegates, we can use lambda expressions to create a delegate and invoke it.

Before getting into an example, let us explore the Func<T,TResult> family. We currently have,

image

A Simple example would be,

Func<string, bool> SampleFunction = n =>n.Contains(‘c’);

SampleFunction(“Chirstchurch”);

The above code block looks fairly simple and actually we see that we can eliminate Named Methods and Anonymous Methods now and directly make use of lambda expressions!

Coming back to our example, we can now simplify our FilterNames Utility function to something like this,

public static List<string> FilterNamesUsingFuncDelegates

(string[] names,Func<string,bool> customFilter)

{

List<string> NamesList = new List<string>();

foreach (string name in names)

{

if (customFilter(name))

NamesList.Add(name);

}

return NamesList;

}

Yes, you are right; we no need to declare any delegate now and make use of the available function delegates as Predicates!

Predicates were introduced in .NET 2.0 and are defined as (from MSDN),

Represents the method that defines a set of criteria and determines whether the specified object meets those criteria

You can read more about Predicates here

We can come across the same in LINQ when you use Standard Query Operators. If you remember our LINQ example, we have actually seen this,

IEnumerable<string> query = names

.Where(n => n.Equals(matchName))

.Select();

And Where clause syntax is,

clip_image008

You can download the sample application here

Useful Resources

1) Named Methods

2) Anonymous Methods

3) Standard Query Operators





A simple Twitter client to demonstrate BackgroundWorker

5 04 2008

We have always had problems when we want to execute some operation that might take long time in a separate thread and at the same time updating UI components.

With BackgroundWorker class, we can simplify this process and makes it very simple for us to do asynchronous operations.

We initialize the BackgroundWorker and register for their events and run it asynchronously. So, when those events like WorkCompleted, ProgressChanged occurs, you are taken to your callback which is in the thread that started the BackgroundWorker.

BackgroundWorker LoginWorker = new BackgroundWorker();

LoginWorker.DoWork += new DoWorkEventHandler(worker_DoWork);

LoginWorker.RunWorkerCompleted +=new

RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);

LoginWorker.WorkerSupportsCancellation = true;

I have developed a small (very) basic Twitter client to demonstrate the BackgroundWorker class

You can download the sample here








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