Why my Indexer is not working?

Question

Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters.

I have a code like this

class StudentMemento
 {
 Student student;
 public Student this[int index]
 {
 get { return student; }
 set { student = new Student { time = DateTime.Now }; }
 }
 }
 class Client
 {
 static void Main()
 {
 StudentMemento s = new StudentMemento();
 Student s1 = s[1];
 Student s2 = s[2];
 Student s3 = s[1];
 Console.Read();
 }
 }

According to the documentation in msdn i should get an instance of Student in the following members s1,s2 because i am returning an object of Student int the Indexer but i am getting a null reference. Can anyone help me understand, why is that so. Thanks

• Lee: The student field isn't assigned until you call the setter, which you aren't doing in Main.
• McNets: you need a list or an array of students
• Lijin Durairaj: @mcNets i am trying to understand the workings of Indexer

Answer 1

After

StudentMemento s = new StudentMemento();

s.student will be null. The student field is only assigned within the indexer setter, so you need to call that before calling the getter e.g.

StudentMemento s = new StudentMemento();
s[1] = null;
Student s1 = s[1];
Student s2 = s[2];
Student s3 = s[1];

• Lijin Durairaj: but when i set s[1]=null, s1 gets an object of Student(). But how is the variable s2 is also getting the value when i have not called a setter on s[2]
• Lee: @LijinJohn - There is only one backing field, your indexer doesn't use the index parameter at all.