The 'async' modifier can only be used in methods that have a body.

Problem

I declared a method in my interface as follows.

    public interface IHttpService
    {
        public async  Task<HttpResponseWrapper<Object>> Post<T>(string url, T data);
    }

I am getting the following error when I compile my code

"The 'async' modifier can only be used in methods that have a body."

Solution

The error can be fixed just by removing the async modifier from the method declaration. So the solution is to declare the method signature as follows.

public interface IHttpService
    {
        public  Task<HttpResponseWrapper<Object>> Post<T>(string url, T data);
    }

In C#, an interface cannot specify a method must be implemented as asynchronous. When you implement the interface you can add the async modifier as follows 

public class HttpService : IHttpService
    {      
         public async Task<HttpResponseWrapper<object>> Post<T>(string url, T data)
        {
            throw new NotImplementedException();
        }

    }