select from list by object type

Question

Structure of my project:

class Attachment { ... }
class Photo : Attachment { ... }
class Document : Attachment { ... }

class Page
{
    public List<Attachment> attachments;
                ...
}

I receive pages from the server:

List<Page> pages = ...load pages from server;

I need to get from this list pages which in the Attachments have only objects with type Photo.

How can I do it?

Tim Schmelter · Accepted Answer · 2015-03-25 12:30:17Z

6

You can use OfType:

var photos = attachments.OfType<Photo>();

If you instead want all pages with only photo-attachments:

var pagesWithPhotosOnly = pages.Where(p => p.attachments.All(pa => pa is Photo));

answered Mar 25, 2015 at 12:30

Tim Schmelter

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Comments

Andrei V · Accepted Answer · 2015-03-25 12:37:53Z

5

One way of achieving this is iterating the list and checking the type of the Attachment.

var photos = attachments.Where(a => a is Photo);

Another method, as pointed in the comments and @TimSchmelter's answer, is to directly use the OfType extension method, which is arguably more "expressive" than using Where.

edited Mar 25, 2015 at 12:37

answered Mar 25, 2015 at 12:29

Andrei V

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2 Comments

crashmstr Over a year ago

Another potential benefit of OfType instead of a Where like above is that OfType returns the items that are the type as the type (no additional casting required).

Andrei V Over a year ago

@crashmstr, point taken. If you'd need to access the member of the Photo objects after the filtering, OfType would be the way to go.

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