Lambda expression with valueof an generic IEnumerable

Question

I have the following statement:

AnotherClass temp = myCustomList
    .Where(x => x.bTyp != null && x.bTyp is IEnumerable<T>)
    .FirstOrDefault();`

The statement above says that temp is null, but it shouln't be.

T gets as a value a generic List of MyCustomClass like List<MyCustomClass>.

x.bTyp has as a value typeof(IEnumerable<MyCustomClass>)).

The debugger gives me for myCustomList something like this:

bTyp = {System.Collections.Generic.IEnumerable1[...MyCustomClass]}`

How should I rewrite the statement that temp is not null and will return an result ?

Can you just check if the object itself is null and not the type? — Jacobr365, Apr 07 '16 at 14:59
http://stackoverflow.com/questions/2404993/is-it-possible-to-define-a-generic-lambda — willaien, Apr 07 '16 at 15:04
@willaien Actually `x.bTyp` has a dynamic data type(it's a property), but its value is at this moment something like this `typeof(IEnumerable))` — kkkk00999, Apr 07 '16 at 15:07
If you remove `x.bTyp is IEnumerable` condition `temp` is still `null`? — Arturo Menchaca, Apr 07 '16 at 15:12
Ok, but when `x.bTyp` is `dynamic` it will be `IEnumerable` ,that's what I thought of ?! — kkkk00999, Apr 07 '16 at 15:22
and are you sure that the current value of x.bTyp is IEnumerable? because this is actually the problem — Arturo Menchaca, Apr 07 '16 at 15:35

Robear · Answer 1 · 2016-04-07T16:08:47.733

0

Temp is null because there Where() call returns 0 results and FirstOrDefault() is returning the default (which is null).

To debug, place the cursor in the lambda expression and add a breakpoint (default: F9). Run the program.

When the debugger hits the breakpoints, place your boolean expressions ( x.bTyp != null and x.bTyp is IEnumerable) in the watch windows to verify the desired result. Chances are you're missing something here.

edited Apr 07 '16 at 16:08

answered Apr 07 '16 at 15:16

Robear

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ok, but the name 'x' does not exist in the current context, before, during and after that statement, because its an lambda expression ... – kkkk00999 Apr 07 '16 at 15:28
1

Are you sure the breakpoint is *inside* of the lambda expression? Are you using Visual Studio? If so, what version?I added an image for clarification. – Robear Apr 07 '16 at 16:09
Thank you for the tip with the debugger.When I type `x.bTyp` I get(shortend it) `{System.Collections.Generic.IEnumerable'1[...MyCustomClass}....IsGenericType: true...UnderlyingSystemType: {Name = "IEnumerable'1" FullName = "System.Collections.Generic.IEnumerable'1[[...MyCustomClass}` and `T` is `System.Collections.Generic.List<...MyCustomClass>` hope this helps – kkkk00999 Apr 08 '16 at 06:07

Lambda expression with valueof an generic IEnumerable

1 Answers1