Using Array.FindAll method to find subarray which meets criteria

Question

I have an application in Visual Basic.Net and need to find all elements within an array which meet a certain condition.

Dim result As my_obj() = Array.FindAll(lstData, HasToBeSent)

Where the function HasToBeSent is defined like this:

Private Function HasToBeSent(ByVal cta As my_obj) As Boolean
    Return cta.IsSent
End Function

However this doesn't compile, it says I haven't specified an argument for the parameter cta in Private Function HasToBeSent(ByVal cta As my_obj) As Boolean

I am using Visual Studio 2005, therefore I have VB.Net 8.0. I am guessing the suggested answer is for higher versions of VB.Net. Because when I replace the previous code with

Dim result As my_obj() = Array.FindAll(lstData, Function(cta) HasToBeSent(cta))

It says: "expression expected"

How can I solve this?

@soph: That is not VB6 code. It is vb.net. As such, I've removed the incorrect tag. — Deanna
– Deanna, Commented May 17, 2013 at 22:22

Cᴏʀʏ · Accepted Answer · 2013-05-20 13:10:01Z

4

Keep your HasToBeSent definition but add the Shared keyword to it to make it static (actually this is probably optional, but since this code doesn't rely on anything else in your class, it's probably a good design decision anyway).

Private Shared Function HasToBeSent(ByVal cta As my_obj) As Boolean
    Return cta.IsSent
End Function

And then in Array.FindAll(), give it the "address of" your function:

Array.FindAll(lstData, AddressOf HasToBeSent)

If you upgrade to a newer version of VB, then you can inline a delegate:

Array.FindAll(lstData, Function(cta) cta.IsSent)

To keep the HasToBeSent function, you can simply call that instead:

Array.FindAll(lstData, Function(cta) HasToBeSent(cta))

edited May 20, 2013 at 13:10

answered May 17, 2013 at 21:14

Cᴏʀʏ

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9 Comments

Soph Over a year ago

I just edited my question explaining why your solution doesn't work for me. Could you take a look at it?

Cᴏʀʏ Over a year ago

@Soph: I updated my answer. Hopefully we got it this time! :)

Victor Zakharov Over a year ago

If LINQ is supported, I would go with this: lstData.Where(Function(cta) cta.IsSent).ToArray, just find it more intuitive.

Cᴏʀʏ Over a year ago

@Neolisk: I would agree, but LINQ support didn't show up until VB.NET/VS 2008 :/

Cᴏʀʏ Over a year ago

@Soph: My bad. It's been a while since I've used 2005. I updated again -- read it carefully, the change is very subtle.

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