Problem calling ASP.NET web api from another API .

Question

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I want to call api method 2 from external controller method 1 but it throw me exception like below.please help me what is the solution of this?
if i call direct method to then it working properly. so why it is not calling from method-1 and throw me exception like below.

{"message":"An error has occurred.","exceptionMessage":"Value cannot be null.\r\nParameter name: request","exceptionType":"System.ArgumentNullException","stackTrace":" at System.Net.Http.HttpRequestMessageExtensions.CreateResponse[T](HttpRequestMessage request, HttpStatusCode statusCode, T value, ......}

Method 1:
[Route("api/external/vehicles/update")]
public async Task<httpresponsemessage> ExternalCustomerUpdateVehicle(VehicleRequest vehicleRequest)
{
VehicleController VCobj = new VehicleController();
return await VCobj.CustomerUpdateVehicle(vehicleRequest);
}

Method 2:
[Route("api/vehicles/update")]
public async Task<httpresponsemessage> CustomerUpdateVehicle(VehicleRequest vehicleRequest)
{
//code part
return this.Request.CreateResponse(HttpStatusCode.Created, responseText);
}

What I have tried:

try like this but not succeed.
HttpResponseMessage result = await VCobj.CustomerUpdateVehicle(vehicleRequest);
if(result.IsSuccessStatusCode)
{
return result;
}
else
{
String responseText = "External Customer update Vehicle Calling Fail";
return this.Request.CreateResponse(HttpStatusCode.Created, responseText);
}

Posted 9-Jun-16 2:40am

piyushpiyush

Updated 12-Jun-16 18:32pm

v4

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Comments

Sergey Alexandrovich Kryukov 9-Jun-16 10:18am

In what line? Use the debugger. With delegated calls, like asynchronous, the exception information may be not immediately seen, so pay attention for Exception.InnerException. Ultimately, locate the code throwing original exception and inspect with the debugger: what is assumed to be null but actually is null. If debugging is not possible, use logging.
—SA

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Sergey Alexandrovich Kryukov · Answer 1 · 2016-06-09T04:21:00

Please see my comment to the question.

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferences by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA