If I have a object like:
public class Person
{
public int id {get;set;}
public string name {get;set;}
}
And I want the behavior:
Person a = new Person();
Person b = new Person();
a == b;
and that a == b returns true, do I have to override the Object.Equals() method? or is there some other way of doing it without overriding the Equals method?
EDIT
I want to compare data, as I want to know if a external method that I call returns a new object or a object with different data than a new object
There are a couple of ways you can do this. By default Equals()
and ==
check for reference equality, meaning:
Person a = new Person();
Person b = a:
a.Equals(b); //true
a == b; //true
And therefore, the objects are not compared for value equality, meaning:
Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };
a.Equals(b); //false
a == b; //false
To compare objects for their values you can override the Equals()
and GetHashcode()
methods, like this:
public override bool Equals(System.Object obj)
{
if (obj == null)
return false;
Person p = obj as Person;
if ((System.Object)p == null)
return false;
return (id == p.id) && (name == p.name);
}
public bool Equals(Person p)
{
if ((object)p == null)
return false;
return (id == p.id) && (name == p.name);
}
public override int GetHashCode()
{
return id.GetHashCode() ^ name.GetHashCode();
}
Now you will see other results when comparing:
Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };
Person c = a;
a == b; //false
a == c; //true
a.Equals(b); //true
a.Equals(c); //true
The ==
operator is not overridden and therefore still does reference comparison. This can be solved by overloading it as well as the !=
operator:
public static bool operator ==(Person a, Person b)
{
if (System.Object.ReferenceEquals(a, b))
return true;
if ((object)a == null || (object)b == null)
return false;
return a.id == b.id && a.name == b.name;
}
public static bool operator !=(Person a, Person b)
{
return !(a == b);
}
Now running the checks results in following:
Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };
Person c = a;
a == b; //true
a == c; //true
a.Equals(b); //true
a.Equals(c); //true
More reading: