Question

Student class

public class Student
{
    string name;        
    List<SubjectInfo> subjectInfoList;    
    ....
}

List<SubjectInfo> List can have different number of SubjectInfo objects for different students.

SubjectInfo struct

public struct SubjectInfo
{
    string subjectCode;
    int marks;
    ...
}

I want to display student object detail on a window. Since List have different number of object count I used ItemsControl and used dataTemplate.

Binding a student object works perfectly.

Student student = new Student("Joe", new List<SubjectInfo>() { new SubjectInfo("Subject1", 50), new SubjectInfo("Subject2", 70) });  
StudentGrid.DataContext = student;  

But this TwoWay binding is not working for SubjectInfo(Changing value from UI will not caught by the codebehind)
But if change SubjectInfo struct to SubjectInfo class it works.

Cannot understand why. Please advice me.

Answer 1

By assigning a SubjectInfo to DataContext, it is copied (because it is a struct/ValueType), that’s why the binding does not work. This is in most cases not what you want. I suggest you use a class for SubjectInfo instead.

You should be aware of the differences between class and struct. The C# Specification (V4.0) summarizes them like this (in section 11.3):

• Structs are value types (§11.3.1).
• All struct types implicitly inherit from the class System.ValueType (§11.3.2).
• Assignment to a variable of a struct type creates a copy of the value being assigned (§11.3.3).
• The default value of a struct is the value produced by setting all value type fields to their default value and all reference type fields to null (§11.3.4).
• Boxing and unboxing operations are used to convert between a struct type and object (§11.3.5).
• The meaning of this is different for structs (§7.6.7).
• Instance field declarations for a struct are not permitted to
  include variable initializers (§11.3.7).
• A struct is not permitted to declare a parameterless instance constructor (§11.3.8).
• A struct is not permitted to declare a destructor (§11.3.9).