c# gtin End If End Sub in Visual C#.NET

Creator EAN13 in Visual C#.NET End If End Sub

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Public Shadows Sub CancelAsync(ByVal userState As Object) MyBase.CancelAsync(userState) End Sub //C# public event GetCompanyNameCompletedEventHandler GetCompanyNameCompleted; [System.Web.Services.Protocols.SoapDocumentMethodAttribute( "http://tempuri.org/GetCompanyName", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle= System.Web.Services.Protocols.SoapParameterStyle.Wrapped)] public string GetCompanyName(string tickerSymbol) { object[] results = this.Invoke("GetCompanyName", new object[] { tickerSymbol}); return ((string)(results[0])); } /// <remarks/> public void GetCompanyNameAsync(string tickerSymbol) { this.GetCompanyNameAsync(tickerSymbol, null); } /// <remarks/> public void GetCompanyNameAsync(string tickerSymbol, object userState) { if ((this.GetCompanyNameOperationCompleted == null)) { this.GetCompanyNameOperationCompleted = new System.Threading.SendOrPostCallback( this.OnGetCompanyNameOperationCompleted); } this.InvokeAsync("GetCompanyName", new object[] { tickerSymbol}, this.GetCompanyNameOperationCompleted, userState); } private void OnGetCompanyNameOperationCompleted(object arg) { if ((this.GetCompanyNameCompleted != null)) { System.Web.Services.Protocols.InvokeCompletedEventArgs invokeArgs = ((System.Web.Services.Protocols.InvokeCompletedEventArgs) (arg)); this.GetCompanyNameCompleted(this, new GetCompanyNameCompletedEventArgs(invokeArgs.Results, invokeArgs.Error, invokeArgs.Cancelled, invokeArgs.UserState)); } } [System.CodeDom.Compiler.GeneratedCodeAttribute("System.Web.Services", "2.0.50727.42")] public delegate void GetCompanyNameCompletedEventHandler( object sender, GetCompanyNameCompletedEventArgs e);

[System.CodeDom.Compiler.GeneratedCodeAttribute("System.Web.Services", "2.0.50727.42")] [System.Diagnostics.DebuggerStepThroughAttribute()] [System.ComponentModel.DesignerCategoryAttribute("code")] public partial class GetCompanyNameCompletedEventArgs : System.ComponentModel.AsyncCompletedEventArgs { private object[] results; internal GetCompanyNameCompletedEventArgs(object[] results, Exception exception, bool cancelled, object userState) :

base(exception, cancelled, userState) {

this.results = results;

public string Result {

get {

this.RaiseExceptionIfNecessary();

return ((string)(this.results[0]));

} } }

If you examine this code closely, you ll probably see the specific code that allows for asynchronous invocation. (Hint: look for async.) Now, change the original code defi nition slightly to call the GetCompanyNameAsync method:

'VB Public Sub GetTickerSymbol() Dim Lookup As New StockLookupService() Console.WriteLine(Lookup.GetCompanyNameAsync("MSFT")) End Sub //C# public static void GetTickerSymbol() { StockLookupService Lookup = new StockLookupService(); Console.WriteLine(Lookup.GetCompanyNameAsync("MSFT")); }

If you try to compile and run this code, it fails, indicating that the return type from the method call isn t valid. Lest there be any confusion, this modified code won t work. That s because calling an asynchronous method is a little more involved. The answer to why the return type from the method call is no longer valid rests in the proxy class, the relevant portions of which are provided here:

'VB Public Overloads Sub GetCompanyNameAsync(ByVal tickerSymbol As String) Me.GetCompanyNameAsync(tickerSymbol, Nothing)

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End Sub Public Overloads Sub GetCompanyNameAsync(ByVal tickerSymbol As String, _

ByVal userState As Object)

Me.GetCompanyNameOperationCompleted = _ AddressOf Me.OnGetCompanyNameOperationCompleted End If Me.InvokeAsync("GetCompanyName", New Object() {tickerSymbol}, _ Me.GetCompanyNameOperationCompleted, userState)

//C# public void GetCompanyNameAsync(string tickerSymbol) {

this.GetCompanyNameAsync(tickerSymbol, null);

public void GetCompanyNameAsync(string tickerSymbol, object userState) {

if ((this.GetCompanyNameOperationCompleted == null)) {

new System.Threading.SendOrPostCallback(

this.OnGetCompanyNameOperationCompleted);

this.InvokeAsync("GetCompanyName", new object[] {

tickerSymbol}, this.GetCompanyNameOperationCompleted,

userState);

The most glaring difference is the return type. Notice that a string is no longer returned. In fact, the Visual Basic .NET method signature now specifies a Sub (which indicates there is no return type) and the C# return type now specifies void (which also indicates lack of a return type). How do you handle this situation and make an asynchronous call

One adage of object-oriented design is that classes should be closed for modification but open for extension. Although I could write a few chapters on this principle alone, it essentially means that after you create a class, the interface for it shouldn t change. If you have a method named GetStockSymbol that accepts a single string argument and returns a string, you should not change the return type, change the parameter type, or add or remove parameters. People incorrectly assume that this principle means that the actual implementation of the method should never be changed. If this were the case, then every time you fixed a bug you d be violating good object-oriented pro gramming design principles, which clearly isn t the case. For some reason, many developers who are otherwise careful not to change the interface of a tra ditional class have no such compunction when it comes to Web services. Keep in mind that from the client s perspective, there is literally no difference between calling a Web service s method and any other method. Remember that a proxy class is created that matches the Web service, and objects instantiated from this proxy class contain the methods that are invoked. Any changes that