This PDF is related to Rajpat Systems Part. This PDF contains Indexers in C#, Partial Classes in C#, Partial Method in C#, "Knowledge Is Free Lets Share It"

1. What Is an Indexer?

2. • An indexer is a set of get and set accessors,
similar to those of properties

3. Indexers and Properties
Indexers and properties are similar in many ways.
• • Like a property, an indexer does not allocate
memory for storage.
• • Both indexers and properties are used primarily
for giving access to other data members with
which they are associated, and for which they
provide set and get access.
– – A property is usually accessing a single data
member.
– – An indexer is usually accessing multiple data
members.

4. Some additional points
• • An indexer can have either one or both of the
accessors.
• • Indexers are always instance members; hence,
an indexer cannot be declared static.
• • Like properties, the code implementing the get
and set accessors does not have to be
• associated with any fields or properties. The code
can do anything, or nothing, as long as the get
accessor returns some value of the specified
type.

5. Declaring an Indexer
• • An indexer does not have a name. In place of
the name is the keyword this.
• • The parameter list is between square
brackets.
• • There must be at least one parameter
declaration in the parameter list.

6. Declaring an Indexer

7. Comparing an indexer declaration to a
property declaration

8. The set Accessor
When the indexer is the target of an assignment,
the set accessor is called, and receives two
items of data.
– • An implicit parameter, named value, where
value holds the data to be stored.
– • One or more index parameters that represent
where it should be stored.

9. The get Accessor
• When the indexer is used to retrieve a value,
the get accessor is called with one or more
index parameters.
• The code in the get accessor body must
examine the index parameters, determine
which field they represent, and return the
value of that field.

10. • • It has the same parameter list as in the
indexer declaration.
• • It returns a value of the same type as the
indexer.

11. More About Indexers
As with properties, the get and set accessors
cannot be called explicitly. Instead, the get
accessor is called automatically when the
indexer is used in an expression for a value.
The set accessor is called automatically when
the indexer is assigned a value with the
assignment statement.

13. • class Class1 • Temp1 = value; // Note the implicit
• { variable "value".
• int Temp0; // Private field • }
• int Temp1; // Private field • }
• public int this [ int index ] // The indexer • }
• { • class Example
• get • {
• { • static void Main()
• return ( 0 == index ) // Return value of • {
either Temp0 or Temp1 • Class1 a = new Class1();
• ? Temp0 • Console.WriteLine("Values -- T0: {0}, T1:
• : Temp1; {1}", a[0], a[1]);
• } • a[0] = 15;
• set • a[1] = 20;
• { • Console.WriteLine("Values -- T0: {0}, T1:
• if( 0 == index ) {1}", a[0], a[1]);
• Temp0 = value; // Note the implicit • }
variable "value". • }
• else

14. Access Modifiers on Accessors
There are several restrictions on the access
modifiers of accessors.
– • An accessor can have an access modifier only if
the member (property or indexer) has both a get
accessor and a set accessor.
– • Although both accessors must be present, only
one of them can have an access modifier.
– • The access modifier of the accessor must be
strictly more restrictive than the access level of the
member.

15. Hierarchy of strictly restrictive accessor
levels

16. Indexer Overloading
• class MyClass
• {
• public string this [ int index ]
• {
• get { ... }
• set { ... }
• }
• public string this [ int index1, int index2 ]
• {
• get { ... }
• set { ... }
• }
• public int this [ float index1 ]
• {
• get { ... }
• set { ... }
• }
• ...
• }

17. Partial Classes and Partial Types

18. Partial Class
• The declaration of a class can be partitioned
among several partial class declarations.
– • Each of the partial class declarations contains
the declarations of some of the class members.
– • The partial class declarations of a class can be in
the same file or in different files.

19. • Type modifier
• partial class MyPartClass // Same class name as following
• {
• member1 declaration
• member2 declaration
• ...
• }
• Type modifier
• partial class MyPartClass // Same class name as preceding
• {
• member3 declaration
• member4 declaration
• ...
• }

20. • All the partial class declarations comprising a
class must be compiled together.
• A class using partial class declarations has the
same meaning as if all the class members
were declared within a single class declaration
body.
• Besides classes, you can also create two other
partial types:
– • Partial structs.
– • Partial interfaces.

21. Partial Methods
• Partial methods are methods that are declared in
two parts in a partial class.
• The two parts of the partial method are:
– • The defining partial method declaration gives the
signature and return type, and the implementation
part of the declaration consists of only a semicolon.
– • The implementing partial method declaration gives
the signature, return type, and also the
implementation in the normal format of a statement
block.

22. The important things to know
• • Both the defining and implementing declaration must
match in signature and return type. The signature and
return type have the following characteristics:
– – The contextual keyword partial must be included in both the
defining and implementing declarations immediately before the
keyword void.
– – The signature cannot include access modifiers⎯making partial
methods implicitly private.
– – The return type must be void.
– – The parameter list cannot contain out parameters.
• • You can have a defining partial method without an
implementing partial method. In this case, the compiler
removes the declaration and any calls to the method made
inside the class. If, however, the class has an implementing
partial method, it must also have a defining partial method.