[C#]
using System.Web.Services;
using System.Data;
using System;
// This imports the proxy class for the XML Web services
// that the sample communicates with.
using AsyncWS.localhost;namespace AsyncWS
{
[WebService(Namespace="http://www.contoso.com/")]
public class MyService : System.Web.Services.WebService
{
public RemoteService remoteService;
public MyService()
{
remo teService = new RemoteService();
} [WebMethod]
public IAsyncResult BeginGetAuthorRoyalties(String Author,
AsyncCallback callback, Object asyncState)
{
// Saves the current state for the call that gets the author's
// royalties.
AsyncStateChain state = new AsyncStateChain();
state.originalState = asyncState;
state.Author = Author;
state.originalCallback = callback; // Creates an intermediary callback.
AsyncCallback chainedCallback = new
AsyncCallback(AuthorRoyaltiesCallback);
return remoteService.BeginGetAuthors(chainedCallback,state);
}
// Intermediate method to handle chaining the
// asynchronous calls.
public void AuthorRoyaltiesCallback(IAsyncResult ar)
{
AsyncStateChain state = (AsyncStateChain)ar.AsyncState;
RemoteService rs = new RemoteService(); // Gets the result from the call to GetAuthors.
Authors allAuthors = rs.EndGetAuthors(ar); Boolean found = false;
// Verifies that the requested author is valid.
int i = 0;
DataRow row;
while (i ＜ allAuthors.authors.Rows.Count && !found)
{
row = allAuthors.authors.Rows[i];
if (row["au_lname"].ToString() == state.Author)
{
found = true;
}
i++;
}
if (found)
{
AsyncCallback cb = state.originalCallback;
// Calls the second XML Web service, because the author is
// valid.
rs.BeginReturnedStronglyTypedDS(state.Author,cb,state);
}
else
{
// Cannot throw the exception in this function or the XML Web
// service will hang. So, set the state argument to the
// exception and let the End method of the chained XML Web
// service check for it.
ArgumentException ex = new ArgumentException(
"Author does not exist.","Author");
AsyncCallback cb = state.originalCallback;
// Call the second XML Web service, setting the state to an
// exception.
rs.BeginReturnedStronglyTypedDS(state.Author,cb,ex);
}
} [WebMethod]
public AuthorRoyalties EndGetAuthorRoyalties(IAsyncResult asyncResult)
{
// Check whehter the first XML Web service threw an exception.
if (asyncResult.AsyncState is ArgumentException)
throw (ArgumentException) asyncResult.AsyncState;
else
return remoteService.EndReturnedStronglyTypedDS(asyncResult);
}
}
// Class to wrap the callback and state for the intermediate
// asynchronous operation.
public class AsyncStateChain
{
public AsyncCallback originalCallback;
public Object originalState;
public String Author;
}
} [Visual Basic] Imports System.Web.Services
Imports System.Data
Imports System
' This imports the proxy class for the XML Web services
' that the sample communicates with.
Imports AsyncWS_VB.localhost Namespace AsyncWs ＜WebService(Namespace:="http://www.contoso.com/")＞ _
Public Class MyService
Inherits WebService
Public remoteService As remoteService
Public Sub New()
MyBase.New()
remoteService = New localhost.RemoteService()
End Sub
' Defines the Begin method.
＜WebMethod()＞ _
Public Function BeginGetAuthorRoyalties(ByVal Author As String, _
ByVal callback As AsyncCallback, ByVal asyncState As Object) _
As IAsyncResult
' Saves the current state for the call that gets the author's
' royalties.
Dim state As AsyncStateChain = New AsyncStateChain()
state.originalState = asyncState
state.Author = Author
state.originalCallback = callback ' Creates an intermediary callback.
Dim chainedCallback As AsyncCallback = New AsyncCallback( _
AddressOf AuthorRoyaltiesCallback)
' Begin asynchronous communictation with a different XML Web
' service.
Return remoteService.BeginGetAuthors(chainedCallback, state)
End Function ' Intermediate method to handle chaining the asynchronous calls.
Public Sub AuthorRoyaltiesCallback(ByVal ar As IAsyncResult)
Dim state As AsyncStateChain = CType(ar.AsyncState, _
AsyncStateChain)
Dim rs As RemoteService = New RemoteService() ' Gets the result from the call to GetAuthors.
Dim allAuthors As Authors = rs.EndGetAuthors(ar)
Dim found As Boolean = False ' Verifies that the requested author is valid.
Dim i As Integer = 0
Dim row As DataRow
While (i ＜ allAuthors.authors.Rows.Count And (Not found))
row = allAuthors.authors.Rows(i)
If (row("au_lname").ToString() = state.Author) Then
found = True
End If
i = i + 1
End While If (found) Then
Dim cb As AsyncCallback = state.originalCallback
' Calls the second XML Web service, because the author is
' valid.
rs.BeginReturnedStronglyTypedDS(state.Author, cb, state)
Else
' Cannot throw the exception in this function or the XML Web
' service will hang. So, set the state argument to the
' exception and let the End method of the chained XML Web
' service check for it.
Dim ex As ArgumentException = New ArgumentException( "Author does not exist.", "Author")
Dim cb As AsyncCallback = state.originalCallback
' Call the second XML Web service, setting the state to an
' exception.
rs.BeginReturnedStronglyTypedDS(state.Author, cb, ex)
End If
End Sub ' Define the End method.
＜WebMethod()＞ _
Public Function EndGetAuthorRoyalties(ByVal asyncResult As _
IAsyncResult) As localhost.AuthorRoyalties
' Return the asynchronous result from the other XML Web service.
Return remoteService.EndReturnedStronglyTypedDS(asyncResult)
End Function End Class ' Class to wrap the callback and state for the intermediate asynchronous
' operation.
Public Class AsyncStateChain
Public originalCallback As AsyncCallback
Public originalState As Object
Public Author As String
End Class
End Namespace |
