问题
As you know, GetHashCode returns a semi-unique value that can be used to identify an object instance in a collection. As a good practice, it is recommended to override this method and implement your own.
My question is - do you override this method when working on custom objects? If so, what algorithm do you use to generate the unique ID?
I was thinking about generating a GUID and then getting integer data from that identificator.
回答1:
When you override GetHashCode() you also need to override Equals(), operator== and operator!= . And be very careful to meet all the requirements for those methods.
The guidelines are here on MSDN. Most important quote:
It is not a good idea to override operator == in non-immutable types.
回答2:
If you use resharper it can generate the GetHashCode(), Equals and operator method bodies for you.
Access this menu by pressing Alt+Insert.
http://www.jetbrains.com/resharper/webhelp/Code_Generation__Equality_Members.html
回答3:
In my personal usage, I only override when overriding equals method too. Generally, I do this for objects I know that I might run a LINQ to Objects query on, or some other comparison operation.
I usually return, if say a LINQ to SQL entity or DTO object, the primary key value. Whatever you return, if you don't store the value locally, it may produce an unexpected result.
HTH.
回答4:
I would normally override hashcode and equality checking methods for data classes (i.e. classes where the value semantics makes sense). Have a look at this question for a common implementation. If you do override hashcode override equals. Using a GUID is a pretty terrible idea because you want two objects which are different instances but have the same value to have the same hashcode and for equals to return true.
回答5:
you only need to override GetHashCode if you are overriding Equals. The default GetHashCode is implemented by the runtime in a similar way you wanted to do it - every object has a hidden field assigned by the runtime.
How to override GetHashCode
Actually your IDE should do this for you - when you type "override GetHashCode" the IDE should generate this boilerplate code. Visual Studio does not do it but SharpDevelop does.
回答6:
Generally I use the aggregated GetHashCode from the component properties of the class. E.g.
public class Test
{
public string Text { get; set; }
public int Age { get; set; }
public override GetHashCode()
{
int result =
string.IsNullOrEmpty(Text) ? 0 : Text.GetHashCode()
+ Age.GetHashCode();
return result;
}
}
来源：https://stackoverflow.com/questions/4240467/overriding-gethashcode