convert object list to type array and remove null values

问题

I want to get some data and convert it to a list of objects. From this list I want to select items that are not null and have a specific type. After that I want to convert these object variables to their correct type and return this list as an array.

        ContactEndpoint[] points = (GetContactInformation(contact, ContactInformationType.ContactEndpoints) as List<object>)
            .Select(item => item)
            .Where(item => item != null && item is ContactEndpoint)
            .ConvertAll(item => item as ContactEndpoint)
            .ToArray();

using this code throws an error at ConvertAll

'IEnumerable' does not contain a definition for 'ConvertAll' and no extension method 'ConvertAll' accepting a first argument of type 'IEnumerable' could be found (are you missing a using directive or an assembly reference?)

My syntax seems to be wrong, all I want to do is

get this data (returned as a List of objects)
select all non null values and objects of type ContactEndpoint
return it as an array

How can I fix it?

回答1:

You can use Enumerable.Cast or - since you want to filter - Enumerable.OfType:

So instead of

.Where(item => item != null && item is ContactEndpoint)
.ConvertAll(item => item as ContactEndpoint)

this (since null values never match any type they are filtered out implicitly by OfType):

.OfType<ContactEndpoint>()

ConvertAll is a method of Arrray or List<T>

回答2:

Try this:

ContactEndpoint[] points = (GetContactInformation(contact, ContactInformationType.ContactEndpoints) as List<object>)
            .Where(item => item is ContactEndpoint)
            .Cast<ContactEndpoint>()
            .ToArray();

回答3:

    ContactEndpoint[] points = GetContactInformation(contact, 
                    ContactInformationType.ContactEndpoints) 
        .Where(item => item != null)
        .OfType<ContactEndpoint>()
        .ToArray();

You should not need the as List<object> or the .Select(item => item)

来源：https://stackoverflow.com/questions/52096041/convert-object-list-to-type-array-and-remove-null-values

标签

linq