Question

I have a collection of objects I need to order but not sure how.

There is a string property called, say Prop1, that I want to sort by. And I want to sort based on a List of strings which contain all possible values of Prop1.

List<string> precedence = new List<string>() { "firstPrecedence", "secondPrecedence" ....

How would I implement my CompareTo(object obj) method?

I’m trying with this but don’t really know what i’m doing!

    public int CompareTo(object obj)
    {
        List<string> precedence = new List<string>() { "firstPrecedence", "secondPrecedence", "thirdPrecedence" };

        Filter filterOther = obj as Filter;

        foreach (var item in precedence)
        {
            return String.Compare(filterOther.FilterValue, item);
        }
        return 0;
    }

Answer 1

Well, if your precedence list is known at compile time and you can use it, then you can compare the indexes of the values you are sorting:

private static List<string> Precedence = new List<string>() { "item1", "item2", "item3" }; // etc

public int CompareTo(object obj)
{
    Filter item = obj as Filter; // Assume not null.   
    int otherIndex = Precedence.IndexOf(item.FilterValue);
    int thisIndex = Precedence.IndexOf(this.FilterValue); // Assume 'this' is a Filter

    // This may need to be otherIndex.CompareTo(thisIndex) depending on the direction of sort you want.
    return thisIndex.CompareTo(otherIndex);
}

If the FilterValue value is not in the list, IndexOf will return -1, which will still work in the sorting implementation here, but may sort at the top or bottom of the list… I can never remember which!

Note that the CompareTo method returns either 0, something less than 0, or something greater than 0. Usually, -1, 0, and 1.

Also, there is a generic IComparable<> which will allow you to achieve this in a more strongly-typed way:

public class Filter : IComparable<Filter>
{

}

And I’m sure some clever person will give you a solution in LINQ…