Casting a function

[VBAHole22]

I have a web service that has a webmethod that is supposed to return an ArrayList. The problem is when I build my client application in the object browser the method appears to return an object and not an arraylist.

 

When I try to to say:

 

Dim GetArrayList As ArrayList

GetArrayList = (MyService.ArrayListType)

 

I get an underline and the error is something like 1-dimensional array of system.object cannot be converted to arraylist.

 

Is there something I am missing? Can I convert the object to an Arraylist before the webmethod returns it?

 

<WebMethod(Description:="Return an array of integers")> Public Function ArrayListType() As ArrayList

End Function

[Nerseus]

Can you have your webmethod return something else, like a Hashtable (which is serializable) or a DataSet?

 

Offhand, I don't think you can get the original data from the arraylist over a webservice. It's best to use objects that can be serialized (meaning converted to a format that can go over a stream, like the web).

 

-Nerseus

[VBAHole22]

I see what you are saying there. All I am passing is text. How would I go about using the Dataset? I am a little worried about for the following reason. The thing that generates the text values is another program that I have set a reference to. Its a GIS program called ArcMap. It also has a dataset object and I don't know how to use the one without confounding the other.

 

I do appreciate your help greatly.

 

Seems like dot.net is like the wild west that the internet was at one time. It's every man for himself and there are no rules or regulations (at least that are written down anywhere).

[Derek Stone]

The ArrayList is serializable. It's one of the more commonly used data types in Web Services.

[Nerseus]

Whoops - I had no idea. Any ideas on how to help out, Derek? Do you just have to change the proxy into ArrayList from object, or do something else?

 

-Ner

[VBAHole22]

Must be doing something else wrong: Here is my service webmethod

 

#Region " strArrayList "

<WebMethod(Description:="Return an array of strings")> Public Function strArrayList() As ArrayList

 

Dim strings As New ArrayList(4)

strings.Add("dopey")

strings.Add("grumpy")

strings.Add("sleepy")

strings.Add("jokey")

strings.Add("dumpy")

 

Return strings

End Function

 

#End Region

 

 

And here is my client calling code on another machine:

 

Private Sub TestService()

Dim MyService As New WebService.Service1

 

Dim GetArrayList As ArrayList()

Dim k As String

GetArrayList = (MyService.strArrayList)

 

For i = 0 To UBound(GetArrayList) - 1

ListBox3.Items.Add(GetArrayList(i))

Next

 

end Sub

 

I got the underline to go away by adding the () after the dim GetArrayList but now it breaks during runtime and strArrayList is still an object and not an ArrayList.

[VBAHole22]

It's working all of the sudden and the only line I changed was in the webmethod as follows:

 

Dim strings As New ArrayList

 

In the example on MSDN they have ArrayList() but it won't even let me write that. The () disappears after i type it.

 

Oh well.

[VBAHole22]

Almost forgot there was one other important mod that I made. In the client calling code I changed:

 

Dim GetArrayList As ArrayList()

 

to

 

Dim GetArrayList As Object

 

So now it is reading in as an object but I can still parse it out to a listbox as if it were a arraylist.

[VBAHole22]

Of course I am never satisfied with what I have.

 

The issue now is this: I cannot manipulate the arraylist in my client code like I can in my web service code. For instance if I want to sort the list I have to do it in the webservice because in the client code the Object doesn't expose this method. Now an easy way around this would be to include a boolean parameter for sorted or unsorted and figure it out in the service. True. But what about the count of elements in the arralylist? I can't pass this back to the calling code can I? I was under the impression that the webmethod (like a regular function) was restricted to passing back a single value. I guess I could stack the count on the end of the arraylist but that seems to be a hack to me. How can I get around this problem?

[bungpeng]

I faced the same problem,

can't return "ArrayList" from web service...

 

any solution?

[PlausiblyDamp]

try

Dim GetArrayList As ArrayList

and see if that works your original code

Dim GetArrayList As ArrayList()

declared an array of ArrayLists.

[bungpeng]

Don't understand,

I define in Webmethod in XML Web service which return "ArrayList",

but when I call from ASP.NET, this function return "Object", not "ArrayList"...

 

Is there anyway I can retrieve as ArrayList rather than Object?

[PlausiblyDamp]

Could you post the code for the web method in question? Also have you tried refreshing the web reference in the client - just to make sure it was using the most current version of the WSDL.

[pinster]

What about casting your object to an arraylist?

 

CType(Object,ArrayList)

[bungpeng]

What about casting your object to an arraylist?

 

CType(Object,ArrayList)

 

Try before, not working?

Unable to convert to ArrayList,

I think because the Object here is normal array, not ArrayList object,

so can't convert

[Joe Mamma]

Arraylist does not derive from MarshalByValueComponent (which I am assuming you want the entire array.

 

does your array list contain simple value types???

 

try deriving a class from ArrayList applying the [serializable] attribute to it.

 

If that doesn't work you might want to implement the ISerializable interface on your array list derivative.

 

A simple implementation will lock your arraylist to specific types. there are techniques for deriving a universal object serializer but it is beyond the scope of this post.

 

I recommend 'Advanced .NET Remoting' Rammer [apress]

I am waiting for the second edition that is supposed to be out any day now.

 

I have MSPress' .Net Remoting, hich sucks in my opinion.