Partial Class in C#

Partial Class

A partial class is a class whose definition is present in 2 or more files. Each source file contains a section of the class, and all parts are combined when the application is compiled. To split a class definition, use the partial keyword as shown in the example below. Student class is split into 2 parts. The first part defines the study() method and the second part defines the Play() method. When we compile this program both the parts will be combined and compiled. Note that both the parts uses partial keyword and public access modifier.

using System;
namespace PartialClass
{
  public partial class Student
  {
    public void Study()
    {
      Console.WriteLine("I am studying");
    }
  }
  public partial class Student
  {
    public void Play()
    {
      Console.WriteLine("I am Playing");
    }
  }
  public class Demo
  {
    public static void Main()
    {
      Student StudentObject = new Student();
      StudentObject.Study();
      StudentObject.Play();
    }
  }
}

Benefit of partial classes:

 

1) More than one developer can simultaneously write the code for the class.

 

2) You can easily write your code (for extended functionality) for a VS.NET generated class. This will allow you to write the code of your own need without messing with the system generated code.

 

There are a few things that you should be careful about when writing code for partial classes: 

• All the partial definitions must proceed with the key word "Partial".
• All the partial types meant to be the part of same type must be defined within a same assembly and module.
• Method signatures (return type, name of the method, and parameters) must be unique for the aggregated typed (which was defined partially).
• The partial types must have the same accessibility.
• If any part is sealed, the entire class is sealed.
• If any part is abstract, the entire class is abstract.
• Inheritance at any partial type applies to the entire class.

It is very important to keep the following points in mind when creating partial classes.
1. All the parts must use the partial keyword.
2. All the parts must be available at compile time to form the final class.
3. All the parts must have the same access modifiers - public, private, protected etc.
4. Any class members declared in a partial definition are available to all the other parts.
5. The final class is the combination of all the parts at compile time.

What are the advantages of using partial classes?
1. When working on large projects, spreading a class over separate files enables multiple programmers to work on it at the same time.

2. When working with automatically generated source, code can be added to the class without having to recreate the source file. Visual Studio uses this approach when it creates Windows Forms, Web service wrapper code, and so on. You can create code that uses these classes without having to modify the file created by Visual Studio.

Is it possible to create partial structs, interfaces and methods?
Yes, it is possible to create partial structs, interfaces and methods. We can create partial structs, interfaces and methods the same way as we create partial classes.

Will the following code compile?
using System;
namespace PartialClass
{
  public partial class Student
  {
    public void Study()
    {
      Console.WriteLine("I am studying");
    }
  }
  public abstract partial class Student
  {
    public void Play()
    {
      Console.WriteLine("I am Playing");
    }
  }
  public class Demo
  {
    public static void Main()
    {
      Student StudentObject = new Student();
    }
  }
}

No, a compile time error will be generated stating "Cannot create an instance of the abstract class or interface "PartialClass.Student". This is because, if any part is declared abstract, then the whole class becomes abstract. Similarly if any part is declared sealed, then the whole class becomes sealed and if any part declares a base class, then the whole class inherits that base class.

Can you create partial delegates and enumerations?
No, you cannot create partial delegates and enumerations.

Can different parts of a partial class inherit from different interfaces?
Yes, different parts of a partial class can inherit from different interfaces.

Can you specify nested classes as partial classes?
Yes, nested classes can be specified as partial classes even if the containing class is not partial. An example is shown below.

class ContainerClass
{
  public partial class Nested
  {
    void Test1() { }
  }
  public partial class Nested
  {
    void Test2() { }
  }
}

How do you create partial methods?
To create a partial method we create the declaration of the method in one part of the partial class and implementation in the other part of the partial class. The implementation is optional. If the implementation is not provided, then the method and all the calls to the method are removed at compile time. Therefore, any code in the partial class can freely use a partial method, even if the implementation is not supplied. No compile-time or run-time errors will result if the method is called but not implemented. In summary a partial method declaration consists of two parts. The definition and the implementation. These may be in separate parts of a partial class, or in the same part. If there is no implementation declaration, then the compiler optimizes away both the defining declaration and all calls to the method.

The following are the points to keep in mind when creating partial methods.
1. Partial method declarations must begin partial keyword.
2. The return type of a partial method must be void.
3. Partial methods can have ref but not out parameters.
4. Partial methods are implicitly private, and therefore they cannot be virtual.
5. Partial methods cannot be extern, because the presence of the body determines whether they are defining or implementing.

What is the use of partial methods?
Partial methods can be used to customize generated code. They allow for a method name and signature to be reserved, so that generated code can call the method but the developer can decide whether to implement the method. Much like partial classes, partial methods enable code created by a code generator and code created by a human developer to work together without run-time costs.

Arrays in C#

1. What are the 3 different types of arrays that we have in C#?
• Single Dimensional Arrays
• Multi Dimensional Arrays also called as rectangular arrays
• Array Of Arrays also called as jagged arrays

using System;

class Program

{

    static void Main()

    {

        // Declare local jagged array with 3 rows.

        int[][] jagged = new int[3][];

        // Create a new array in the jagged array, and assign it.

        jagged[0] = new int[2];

        jagged[0][0] = 1;

        jagged[0][1] = 2;

        // Set second row, initialized to zero.

        jagged[1] = new int[1];

        // Set third row, using array initializer.

        jagged[2] = new int[3] { 3, 4, 5 };

        // Print out all elements in the jagged array.

        for (int i = 0; i < jagged.Length; i++)

        {

            int[] innerArray = jagged[i];

            for (int a = 0; a < innerArray.Length; a++)

            {

               Console.Write(innerArray[a] + " ");

            }

            Console.WriteLine();

        }

    }

}

Output

"1 2"

"0"

"3 4 5"

Description. It declares a jagged array. The word 'jagged' doesn't even exist in the C# language, meaning that you don't need to use this word in your code. Jagged is just a descriptive variable name I use.
Initializations used. It initializes some values in the jagged array. There are lots of square brackets. This is very different from a 2D array, which uses commas instead of pure brackets.
Assigning jagged arrays. It assigns an array at the second index. Above you should see that indexes in the array are assigned to new int[] arrays. This is because the jagged array only allocates the list of empty references to arrays at first. You have to make your own arrays to put in it. We see the array initializer syntax here, which is less verbose than some other ways.
Looping over jagged arrays. You will want to examine each item in the jagged array. We must call Length first on the array of references, and then again on each inner array. The Console calls above are just for the example.

What is the difference between arrays in C# and arrays in other programming languages?
Arrays in C# work similarly to how arrays work in most other popular languages There are, however, a few differences as listed below

1. When declaring an array in C#, the square brackets ([]) must come after the type, not the identifier. Placing the brackets after the identifier is not legal syntax in C#.
int[] IntegerArray; // not int IntegerArray[];

2. Another difference is that the size of the array is not part of its type as it is in the C language. This allows you to declare an array and assign any array of int objects to it, regardless of the array's length.

int[] IntegerArray; // declare IntegerArray as an int array of any size
IntegerArray = new int[10]; // IntegerArray is a 10 element array
IntegerArray = new int[50]; // now IntegerArray is a 50 element array


Are arrays in C# value types or reference types?
Reference types.

What is the base class for all arrays in C#?
System.Array

How do you sort an array in C#?
The Sort static method of the Array class can be used to sort array items.

Give an example to print the numbers in the array in descending order?
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
//Print the numbers in the array without sorting
Console.WriteLine("Printing the numbers in the array without sorting");
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
//Sort and then print the numbers in the array
Console.WriteLine("Printing the numbers in the array after sorting");
Array.Sort(Numbers);
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
//Print the numbers in the array in descending order
Console.WriteLine("Printing the numbers in the array in descending order");
Array.Reverse(Numbers);
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
}
}
}

What property of an array object can be used to get the total number of elements in an array?
Length property of array object gives you the total number of elements in an array. An example is shown below.
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
Console.WriteLine("Total number of elements = " +Numbers.Length);
}
}
}

Give an example to show how to copy one array into another array?
We can use CopyTo() method to copy one array into another array. An example is shown below.
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
int[] CopyOfNumbers=new int[5];
Numbers.CopyTo(CopyOfNumbers,0);
foreach (int i in CopyOfNumbers)
{
Console.WriteLine(i);
}
}
}
}

Can you use foreach iteration on arrays in C#?
Yes, since array type implements IEnumerable, you can use foreach iteration on all arrays in C#.

Master Pages in ASP.NET

1. What are Master Pages in ASP.NET? or What is a Master Page?

ASP.NET master pages allow you to create a consistent layout for the pages in your application. A single master page defines the look and feel and standard behavior that you want for all of the pages (or a group of pages) in your application. You can then create individual content pages that contain the content you want to display. When users request the content pages, they merge with the master page to produce output that combines the layout of the master page with the content from the content page.

What are the 2 important parts of a master page?
The following are the 2 important parts of a master page
1. The Master Page itself
2. One or more Content Pages

Can Master Pages be nested?
Yes, Master Pages be nested.

What is the file extension for a Master Page?
.master

How do you identify a Master Page?
The master page is identified by a special @ Master directive that replaces the @ Page directive that is used for ordinary .aspx pages.

Can a Master Page have more than one ContentPlaceHolder?
Yes, a Master Page can have more than one ContentPlaceHolder

What is a ContentPlaceHolder?
ContentPlaceHolder is a region where replaceable content will appear.

How do you bind a Content Page to a Master Page?
MasterPageFile attribute of a content page's @ Page directive is used to bind a Content Page to a Master Page.

Can the content page contain any other markup outside of the Content control?
No.

What are the advantages of using Master Pages?
1. They allow you to centralize the common functionality of your pages so that you can make updates in just one place.
2. They make it easy to create one set of controls and code and apply the results to a set of pages. For example, you can use controls on the master page to create a menu that applies to all pages.
3. They give you fine-grained control over the layout of the final page by allowing you to control how the placeholder controls are rendered.
4. They provide an object model that allows you to customize the master page from individual content pages.

What are the 3 levels at which content pages can be attached to Master Page?
At the page level - You can use a page directive in each content page to bind it to a master page

At the application level - By making a setting in the pages element of the application's configuration file (Web.config), you can specify that all ASP.NET pages (.aspx files) in the application automatically bind to a master page.

At the folder level - This strategy is like binding at the application level, except that you make the setting in a Web.config file in one folder only. The master-page bindings then apply to the ASP.NET pages in that folder.

What is @MasterType directive used for?
@MasterType directive is used to create a strongly typed reference to the master page.

Are controls on the master page accessible to content page code?
Yes, controls on the master page are accessible to content page code.

At what stage of page processing master page and content page are merged?
During the initialization stage of page processing, master page and content page are merged.

Can you dynamically assign a Master Page?
Yes, you can assign a master page dynamically during the PreInit stage using the Page class MasterPageFile property as shown in the code sample below.
void Page_PreInit(Object sender, EventArgs e)
{
this.MasterPageFile = "~/MasterPage.master";
}

Can you access non public properties and non public methods of a master page inside a content page?
No, the properties and methods of a master page must be public in order to access them on the content page.

From the content page code how can you reference a control on the master page?
Use the FindControl() method as shown in the code sample below.
void Page_Load()
{
// Gets a reference to a TextBox control inside
// a ContentPlaceHolder
ContentPlaceHolder ContPlaceHldr = (ContentPlaceHolder)Master.FindControl ("ContentPlaceHolder1");
if(ContPlaceHldr != null)
{
TextBox TxtBox = (TextBox)ContPlaceHldr.FindControl("TextBox1");
if(TxtBox != null)
{
TxtBox.Text = "TextBox Present!";
}
}
// Gets a reference to a Label control that not in
// a ContentPlaceHolder
Label Lbl = (Label)Master.FindControl("Label1");
if(Lbl != null)
{
Lbl.Text = "Lable Present";
}
}

Can you access controls on the Master Page without using FindControl() method?
Yes, by casting the Master to your MasterPage as shown in the below code sample.
protected void Page_Load(object sender, EventArgs e)
{
MyMasterPage MMP = this.Master;
MMP.MyTextBox.Text = "Text Box Found";
}