Silverlight Exclusive Interview Questions and Answers (29) - Page 2

Canvas is the simplest methodology for layout management. It supports absolute positioning using ‘X’ and ‘Y’ coordinates. ‘Canvas.Left’ helps to specify the X co-ordinate while ‘Canvas.Top’ helps to provide the ‘Y’ coordinates.

Below is a simple code snippet which shows how a rectangle object is positioned using ‘Canvas’ on co-ordinates (50,150).

<Canvas x:Name="MyCanvas">

<Rectangle Fill="Blue" Width="100" 

Height="100" 

Canvas.Left="50" 

Canvas.Top="150"/>

</Canvas> 

Below is how the display looks like. When you the run the code the XAML viewer will position the rectangle object on absolute ‘X” and ‘Y’ coordinates.

Grid layout helps you position your controls using rows and columns. It’s very similar to table defined in HTML.

Below is a simple table with two columns and two rows defined using ‘Grid’.  We have shown how the table display looks like. Using the ‘Grid.ColumnDefinition’ we have defined two columns and using ‘Grid.RowDefinition’ we have defined two rows. We have then created 4 text blocks which are then specified in each section using ‘Grid.Column’ and ‘Grid.Row’. For instance to place in the first column we need specify the ‘Grid.Column’ as ‘0’ and ‘Grid.Row’ as ‘0’. We have followed the same pattern for everyone and you can see all the textblocks are placed in the appropriate sections.

As the name so the behavior. Stack allows you to arrange your UI elements vertically or horizontally.
 

For instance below are 4 elements which are arranged in a stack panel element. You can see how the stack aligns / stacks the elements one above other. You can also stack the UI elements horizontally or vertically depending on your layout nature.

You can get a simple source code which demonstrates the three layouts at the end of this article.

To consume WCF service is a 4 steps procedure.

Step1:- Create your WCF Service

The first step is to create your WCF service. When we create a WCF service by default it creates ‘GetData’ function which takes in a integer value and returns back a string saying “You entered 10” , in case you have passed ‘10’ as value to the function. We will try to consume this service in silverlight in the coming steps.

public class Service1 : IService1

{

public string GetData(int value)

{

return string.Format("You entered: {0}", value);

}

}

Step 2 :- Enable cross domain for your WCF service

For this example our WCF service and the silver light web application will be hosted in different IIS website. In other words they will be hosted in different domains. When we talk about different website in other words they are hosted in different domains. For instance it’s possible that your silver light web application is hosted in one domain like www.xyz.com and your WCF service is hosted in different domain i.e. www.pqr.com .

The WCF service needs to enable cross domain facility so that other domains can consume the WCF service.

Figure :- Cross domain

We need to create two XML files (clientaccesspolicy.xml and crossdomain.xml) in the root directory of the WCF service to enable cross domain functionality.

Below is the XML code snippet for clientaccesspolicy.xml.

<?xml version="1.0" encoding="utf-8" ?>

<access-policy>

<cross-domain-access>

<policy>

<allow-from http-request-headers="*">

<domain uri="*"/>

</allow-from>

<grant-to>

<resource include-subpaths="true" path="/"/>

</grant-to>

</policy>

</cross-domain-access>

</access-policy>

Below is the XML code snippet for crossdomain.xml

<?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">

<cross-domain-policy>

<allow-http-request-headers-from domain="*" headers="*"/>

</cross-domain-policy>

Step 3 :- Add the WCF service reference and call the service

Create a simple silverlight application and add the service reference to your silverlight project. In order to call the WCF service we need to define event handlers.To consume the WCF service is a three step procedure. In the first step refer the name space. In second step1 create the object of your WCF service. In the final step we need to create a event handler which will get the results sent by the WCF service.

One of the important points to note is that the function ‘GetData’ is called asynchronously.

Step 4:- Add the WCF service reference and call the service

Finally compile the program and enjoy the output.

Step 1:- Create the Service and Data service contract

Below is a simple customer table which has 3 fields ‘CustomerId’ which is an identity column, ‘CustomerCode’ which holds the customer code and ‘CustomerName’ which has the name of the customer. We will fire a simple select query using WCF and then display the data on the SilverLight grid.

As per the customer table specified above we need to first define the WCF data contract. Below is the customer WCF data contract.
 

[DataContract]

    public class clsCustomer

    {

        private string _strCustomer;

        private string _strCustomerCode;



        [DataMember]

        public string Customer

        {

            get { return _strCustomer; }

            set { _strCustomer = value; }

        }



        [DataMember]

        public string CustomerCode

        {

            get { return _strCustomerCode; }

            set { _strCustomerCode = value; }

        }

    }

We also need to define a WCF service contract which will be implemented by WCF concrete classes.

[ServiceContract]

    public interface IServiceCustomer

    {

        [OperationContract]

        clsCustomer getCustomer(int intCustomer);

    }

Step 2:- Code the WCF service

Now that we have defined the data contract and service contract it’s time to implement the service contract. We have implemented the ‘getCustomer’ function which will return the ‘clsCustomer’ datacontract. ‘getCustomer’ function makes a simple ADO.NET connection and retrieves the customer information using the ‘Select’ SQL query.

public class ServiceCustomer : IServiceCustomer

    {

        public clsCustomer getCustomer(int intCustomer)

        {

            SqlConnection objConnection = new SqlConnection();

            DataSet ObjDataset = new DataSet();

            SqlDataAdapter objAdapater = new SqlDataAdapter();

            SqlCommand objCommand = new SqlCommand("Select * from Customer where CustomerId=" + intCustomer.ToString());

            objConnection.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnStr"].ToString();

            objConnection.Open();

            objCommand.Connection = objConnection;

            objAdapater.SelectCommand = objCommand;

            objAdapater.Fill(ObjDataset);

            clsCustomer objCustomer = new clsCustomer();

            objCustomer.CustomerCode = ObjDataset.Tables[0].Rows[0][0].ToString();

            objCustomer.Customer = ObjDataset.Tables[0].Rows[0][1].ToString();

            objConnection.Close();

            return objCustomer;

        }

    }

Step 3:- Copy the CrossDomain.xml and ClientAccessPolicy.XML file

This WCF service is going to be called from an outside domain, so we need to enable the cross domain policy in the WCF service by creating ‘CrossDomain.xml’ and ‘ClientAccessPolicy.xml’. Below are both the code snippets. The first code snippet is for cross domain and the second for client access policy.

<?xml version="1.0"?>

	<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">

	<cross-domain-policy>

	  <allow-http-request-headers-from domain="*" headers="*"/>

	 </cross-domain-policy>

<?xml version="1.0" encoding="utf-8" ?>

	<access-policy>

	  <cross-domain-access>

	   <policy>

	      <allow-from http-request-headers="*">

	        <domain uri="*"/>

	      </allow-from>

	      <grant-to>

	        <resource include-subpaths="true" path="/"/>

	      </grant-to>

	   </policy>

	  </cross-domain-access>

	</access-policy>

Step 4:- Change the WCF bindings to ‘basicHttpBinding’

Silverlight consumes and generates proxy for only ‘basicHttpBinding’ , so we need to change the endpoint bindings accordingly.

<endpoint address="" binding="basicHttpBinding" contract="WCFDatabaseService.IServiceCustomer">

Step 5:- Add service reference

We need to consume the service reference in silverlight application using ‘Add service reference’ menu. So right click the silverlight project and select add service reference.

Step 6 :- Define the grid for Customer  Name and Customer Code

Now on the silverlight side we will create a ‘Grid’ which has two columns one for ‘CustomerCode’ and the other for ‘CustomerName’. We have also specified the bindings using ‘Binding path’ in the text block.

<Grid x:Name="LayoutRoot" Background="White">

        <Grid.ColumnDefinitions>

	            <ColumnDefinition></ColumnDefinition>

	            <ColumnDefinition></ColumnDefinition>

	        </Grid.ColumnDefinitions>

        <Grid.RowDefinitions>

	            <RowDefinition Height="20"></RowDefinition>

	            <RowDefinition Height="20"></RowDefinition>

	        </Grid.RowDefinitions>

	        <TextBlock x:Name="LblCustomerCode" Grid.Column="0" Grid.Row="0" Text="Customer Code"></TextBlock>

	        <TextBlock x:Name="TxtCustomerCode" Grid.Column="1" Grid.Row="0" Text="{Binding Path=CustomerCode}"></TextBlock>

	        <TextBlock x:Name="LblCustomerName" Grid.Column="0" Grid.Row="1" Text="Customer Name"></TextBlock>

	        <TextBlock x:Name="TxtCustomerName" Grid.Column="1" Grid.Row="1" Text="{Binding Path=Customer}"></TextBlock>

	</Grid>

Step 7:- Bind the WCF service with the GRID

Now that our grid is created its time to bind the WCF service with the grid. So go to the behind code of the XAML file and create the WCF service object.  There are two important points to be noted when we call WCF service using from SilverLight:-

• We need to call the WCF asynchronously, so we have called ‘getCustomerAsynch’. Please note this function is created by WCF service to make asynchronous calls to the method / function.
   
  
• Once the function completes its work on the WCF service it sends back the message to silverlight client.  So we need to have some kind of delegate method which can facilitate this communication. You can see we have created a ‘getCustomerCompleted’ method which captures the arguments and ties the results with the grid ‘datacontext’.
   

public partial class Page : UserControl

		    {

		        public Page()

		        {

		            InitializeComponent();

		            ServiceCustomerClient obj = new ServiceCustomerClient();

	            obj.getCustomerCompleted += new EventHandler<getCustomerCompletedEventArgs>(DisplayResults);

		            obj.getCustomerAsync(1);

		        }

		        void DisplayResults(object sender, getCustomerCompletedEventArgs e)

		        {

		            LayoutRoot.DataContext = e.Result;

		            

		        }

	    }

You can now run the project and see how the SilverLight client consumes and displays the data.

Silverlight does not have ADO.NET

Below are the different ingredients which constitute SilverLight plugin.  One of the important points to be noted is that it does not consist of ADO.NET. In other words you can not directly call ADO.NET code from SilverLight application. Now the other point to be noted is that it has the WCF component. In other words you can call a WCF service.

In other words you can create a WCF service which does database operations and silverlight application will make calls to the same. One more important point to be noted is do not return ADO.NET objects like dataset etc because  SilverLight will not be able to understand the same.

There are three ways provided by Silverlight for layout management is Canvas, Grid and Stack panel. Each of these methodologies fit into different situations as per layout needs.

Canvas – Absolute Positioning

Canvas is the simplest methodology for layout management. It supports absolute positioning using ‘X’ and ‘Y’ coordinates. ‘Canvas.Left’ helps to specify the X co-ordinate while ‘Canvas.Top’ helps to provide the ‘Y’ coordinates.

Below is a simple code snippet which shows how a rectangle object is positioned using ‘Canvas’ on co-ordinates (50,150).

Below is how the display looks like. When you the run the code, the XAML viewer will position the rectangle object on absolute ‘X” and ‘Y’ coordinates.

Grid – Table layout

Grid layout helps you position your controls using rows and columns. It’s very similar to table defined in HTML.

Above is a simple table with two columns and two rows defined using Grid. We have shown how the table display looks like. Using the Grid.ColumnDefinition, we have defined two columns and using Grid.RowDefinition, we have defined two rows. We have then created 4 text blocks which are then specified in each section using Grid.Column and Grid.Row. For instance, to place in the first column, we need specify the Grid.Column as 0 and Grid.Row as 0. We have followed the same pattern for everyone and you can see that all the textblocks are placed in the appropriate sections.

Stack – One Above the Other

As the name says, so the behavior. Stack allows you to arrange your UI elements vertically or horizontally.

For instance, above are 4 elements which are arranged in a stack panel element. You can see how the stack aligns / stacks the elements one above other. You can also stack the UI elements horizontally or vertically depending on the nature of your layout.

Following is the video which demonstrates simple animation in SilverLight: -