custom icomparer error - The type arguments cannot be inferred from the usage

Question

I'm trying to use IComparer with a generic type.

The code below generates the following error: "The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly."

If I remove the custom comparer from the OrderBy call then the code compiles and orders fine, however I need to be able to pass in my icomparer. Also worth noting is that the code below works if i use type of object/string etc. but fails when I try and use generic type

public IQueryable<T> OrderResults<T, TU>(IQueryable<T> queryData, IComparer<TU> customComparer, string sortColumnName)
{
    var sortPropertyInfo = queryData.First().GetType().GetProperty(sortColumnName);
    return queryData.OrderBy(x => sortPropertyInfo.GetValue(x, null), customComparer);
}

score 2 · Accepted Answer · answered Aug 28 '15 at 14:30

Your snippet has some ambiguity caused by the fact that GetValue(x,null) returns type System.Object. Try the following:

public IQueryable<T> OrderResults<T, TU>(IQueryable<T> queryData, IComparer<TU> customComparer, string sortColumnName)
{
    var sortPropertyInfo = queryData.First().GetType().GetProperty(sortColumnName);
    return queryData.OrderBy(x => (TU)sortPropertyInfo.GetValue(x, null), customComparer);
}

This at least doesn't have a compile time error. If you have some code you're using for testing, I can verify that it works....

custom icomparer error - The type arguments cannot be inferred from the usage

1 Answers1