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c#: How to consume webservice methods whose address is unknown at compile-time

I am consuming a webservice from a Java server. The webservice provides me with some methods that need. Up till now I have been using the method where I added the reference of the webservice in the project explorer, typed the address of the webservice and compiled it. But now I need it to pick up the address of the service at runtime from an xml file or something! is that possible?

There is Url property in generated proxy object that you can set at runtime. Covered in Creating the Web Service Proxy article on MSDN.
Sample from the article (shows how to also set credentials, you may also need to set Proxy):
var rs = new ReportExecutionService();
rs.Url = "http://<Server Name>/reportserver/reportexecution2005.asmx?wsdl";
rs.Credentials = System.Net.CredentialCache.DefaultCredentials;
Note that above answer is for case when you don't know exact Url of server till runtime, but you have WSDL/sample server available at design time and able to generate proxy via add web service in VS (or manually).
Alternatively you can call service via other classes implementing "HTTP GET" like HttpClient and configure anything you want, but will need to do your own parsing of results.

Connect to Unknown SOAP Web Service

I would like to build an app in C# that connects to an Apache AXIS web service and performs the following operations via SOAP.
Login in to the server.
POST string data to server
Receive and display server response
Here's the tough part. I do not have access to the server, nor do I know where the .JWS file is located on the server. I was able to get to the WSDL file in my web browser, so I know a "Login" operation exists as well as an operation to take in data.
I have tried accessing the web service via URL, but I keep getting this message:
Hi there, this is an AXIS service!
Perhaps there will be a form for
invoking the service here...
In summary, is there anyway I can connect to this web service when all I have is the URL of the WSDL file? Are web services accessible via URL?
Thank you

Use WCF, and generate client proxies to the web service using the svcutil.exe tool.
running svcutil.exe http://url.to/webservice?WSDL the_wsdl.wsdl /language:C# should generate proxy classes you can use in your C# project, and you'd call the service e.g. like
BasicHttpBinding myBinding = new BasicHttpBinding(); //might not even need these
// 2 lines if you ran svcutil.exe directly on the web service URL
EndpointAddress myEndpoint = new EndpointAddress("http://url.to/webservice");
TestClient client = new TestClient(myBinding,myEndpoint); //the generated classes
// svcutil.exe created
client.SomeOperation(42); // call an SomeOperation of the web service

Thanks for everyone's help. Looking back on this question, I can see how severely confused I was. Here is the solution I followed.
Assuming you know the URL of the WSDL file of the service you wish to connect to then just do the following.
Boot up Visual Studio
On the top toolbar navigate to Data -> Add New Data Source then choose Service in the new dialog
In the address bar, enter the URL of the wsdl file (EXAMPLE: http://server.com/services/displayName?wsdl)
Near the bottom of the dialog, change the namespace to something relevant to the project (EXAMPLE: sampleService)
Now Visual Studio should compile the client proxies for you that you can use to access the web services on your server. To access one of the services, all you need to do is create a new object from the class.
//Example
sampleService.ClassName test = new sampleService.ClassName();
test.displayName("Jack");

See http://msdn.microsoft.com/en-us/library/bb552364.aspx for a starting point

Problem regarding consuming php web service in c# Desktop application

I am developing a c# desktop application and using a webservies which is developed in a php application when i try to consume that application. I just add web REference of that web service and try to access throught the following code
WebReference.TestWSDL pdl = new testingApp.WebReference.TestWSDL();
string copy = pdl.verify("testing");
it throws the error when i try to call the method verify. the error is
Possible SOAP version mismatch: Envelope namespace http://schemas.xmlsoap.org/wsdl/ was unexpected. Expecting http://schemas.xmlsoap.org/soap/envelope/.
and the web service link was like
http://171.139.101.12/code/index.php/webservice/wsdl

The error you are encountering is informing you that when you invoke the webservice, you are being given the WSDL (Web Service Definition Language) for the service - this is the metadata that describes the service functions, but cannot actually be used to invoke the service. Usually, you access the WSDL by appending either "?wsdl" or "wsdl" to the service URI.
There are two elements to the webservice you are attempting to consume.
The actual service exists at:
http://171.139.101.12/code/index.php/webservice
The metadata describing it, which Visual Studio via wsdl.exe used to generate a proxy, resides here:
http://171.139.101.12/code/index.php/webservice/wsdl
You need to edit the properties of the Web Reference and update the address appropriately. Alternatively, you can alter the properties of the pdl variable, and change the endpoint in code.

Getting an Instance of your Web Service Reference

So I believe all you have to do with .NET 2.0 vanilla web services (not WCF) is the following:
1) Add your service reference. In my case I'm using the PayPal WSDL
2) Before you can use any proxy class, you must first create an instance of your service reference
3) Once you create an instance of your service reference, then just do [servicereference].ProxyClassName.Method or whatever you're trying to access from those classes
right?
Ok, so I tried that. I added a service reference and named it SandboxSoapAPI. So that's what you see under references in my C# project.
In code I tried this:
SandboxSoapApi reference = new SandboxSoapApi();
but it doesn't recognize SandboxSoapAPI. Am I doing something wrong? I just want to start calling class methods, etc. with PayPal and I can't seem to get this right.
And if I'm not incorrect, as of .NET 2.0+ it handles the low level sending of the actual request over Http for SOAP web service references?

SandboxSoapAPI is not the SOAP client proxy type name. It's a namespace.
To check this, in VS.NET tick 'show all files' and drill into the Web References, open up the Reference.cs file, you will see the SandboxSoapApi is a subnamespace (not your SOAP client proxy name!) in the project's root namespace.
So either use the fully qualified name:
SandboxSoapAPI.YourProxyType client = new SanboxSoapAPI.YourProxyType();
Or use using SandboxSoapAPI; in your code where you need the SOAP client.

C# SOAP with a custom URL

Okay, simple situation: I'm writing a simple console application which connects to a SOAP web service. I've imported a SOAP Service reference and as a result, my application has a default endpoint build into it's app.config file.
The web service, however, can run on multiple servers and the URL to the proper web service is passed through the commandline parameters of my application. I can read the URL, but how do I connect the web service to this custom URL?
(It should be very simple, in my opinion. It's something I'm overlooking.)

Is this using an auto-generated class deriving from SoapHttpClientProtocol? If so, just set the Url property when you create an instance of the class.

Well, .NET can provide some very useless error messages sometimes. In IIS, the service was configured to AutoDetect cookieless mode. As a result, I had to append "?AspxAutoDetectCookieSupport=1" to the URL. Although that would fix the problem, it was just easier to go to the IIS console, open the properties of the service, go to the ASP.NET tab page, click the "Edit configuration" button, to to "State Management" in the newly popped up screen and change "Cookieless mode" into something other than "AutoDetect"...
Excuse me. Dumb error. Am going to hit myself on the head a few times for this. ;-)

As Jon said, you set the Url, as in:
Namespace.ClassName nwe = new Namespace.ClassName();
nwe.Url = "http://localhost/MyURL/site.asmx";