WebMethod argument validation

I have a straitforward "helloWorld" webService example:

using System;
using System.Web;
using System.Web.Services;

namespace WebServiceTest
{
public class WebServiceTest : System.Web.Services.WebService
{
[WebMethod]
public string HelloWorld(int number)
{
return "Hello World" + number;
}
}
}

How and where can I validate if the "number" is actually an int type If I write a string instead of a number the follwing exception is raise and everything blows up. I know that I need to make a validation before the method receives the arguments, but I do not know where. Could someone help me

System.ArgumentException: Cannot convert 256 to System.Byte.
Parameter name: type ---> System.OverflowException: Value was either too large or too small for an unsigned byte.
at System.Byte.Parse(String s, NumberStyles style, IFormatProvider provider)
at System.String.System.IConvertible.ToByte(IFormatProvider provider)
at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
at System.Convert.ChangeType(Object value, Type conversionType)
at System.Web.Services.Protocols.ScalarFormatter.FromString(String value, Type type)
--- End of inner exception stack trace ---
at System.Web.Services.Protocols.ScalarFormatter.FromString(String value, Type type)
at System.Web.Services.Protocols.ValueCollectionParameterReader.Read(NameValueCollection collection)
at System.Web.Services.Protocols.UrlParameterReader.Read(HttpRequest request)
at System.Web.Services.Protocols.HttpServerProtocol.ReadParameters()
at System.Web.Services.Protocols.WebServiceHandler.Invoke()
at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest()

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WebMethod argument validation

Tony Long
What would your validation code do if it found a string instead of a number Throw an Exception right Guess what! ASP.net does the validation for you and it throws an exception if the validation fails, no need to dirty your hands. It is really up to the client code to validate the number before passing, not your webmethod. If it isn't a number then the method can't do anything anyway. If you want to allow strings then you have to make the parameter a string and convert it inside the method.
pshashnak1
Hi,

You have to declare the input parameter as string and then to convert it to int.

Use a try … catch construct for conversion. If the conversion fails, the variable is not an integer.

Example:

using System;
using System.Web;
using System.Web.Services;

namespace WebServiceTest
{
public class WebServiceTest : ystem.Web.Services.WebService
{
[WebMethod]
public string HelloWorld(string number)

{

try

{

Convert.ToInt32(number);

return "Hello world " + number;

}

catch

{

return "Invalid number";

}

}

}

}

Have a fun!

Valentin

Do not hesitate to contact me!

www.wwv-it.eu

valentin.welter@t-online.de
Sorin Sandu
That is wrong!

Every Web Method has to check the input parameters. That was a very simply case, but what would happen in case of a calendar date input parameter

An exception failure is utmost unwanted and the Web Methods must avoid at all such failures.

Have a fun!

Valentin

MCP C#

Do not hesitate to contact me!

www.wwv-it.eu

valentin.welter@t-online.de
WebMethod argument validation

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