Consume Web API data using HttpClient in c#

HttpClient is a base class for sending HTTP requests and receiving HTTP responses from a resource identified by a URI.

Following code example get movies data in JSON format,

Web API code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using Newtonsoft.Json.Linq;
using Newtonsoft.Json;
using System.Threading;
using System.Net.Http.Headers;
public class RestAPICall
    {
        private const string URL = "https://c4utest.com/api/movies/search";
        private const string urlParameters = "?Title=Bahubali ";
     
       public void  DisplayMoviesFromRestAPI()
        {
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri(URL);
                // List data response.
                HttpResponseMessage response = client.GetAsync(urlParameters).Result; 
                // blocking call
                if (response.IsSuccessStatusCode)
                {
                    // Parse the response body.
                    var dataObjects = response.Content.ReadAsStringAsync().Result; 
                    //data objects
                    Movies deserializedProduct = JsonConvert.DeserializeObject<Movies>(dataObjects);
                    JObject jsonval = JObject.Parse(dataObjects);
                    if (deserializedProduct != null)
                    {
                        Console.WriteLine("Total movies : "+ deserializedProduct.total);
                        Console.WriteLine("Current page : " + deserializedProduct.page);
                        Console.WriteLine("Total pages : " + deserializedProduct.total_pages);
 
                        //first movie details
                        var firstMoviesDetails = deserializedProduct.data.FirstOrDefault();
                        //Display first moview details from collections
                        Console.WriteLine("First movie title : " + firstMoviesDetails.Title);
                        Console.WriteLine("First movie release year : " + firstMoviesDetails.Year);
                        Console.WriteLine("First movie code : " + firstMoviesDetails.imdbID);
 
                        //display all movies details
                        foreach (var movieDetail in deserializedProduct.data)
                        {
                            Console.WriteLine("Movie title : " + movieDetail.Title);
                            Console.WriteLine("Movie release year : " + movieDetail.Year);
                            Console.WriteLine("Movie code : " + movieDetail.imdbID);
                        }
                    }
                }
                else
                {
                    Console.WriteLine("{0} ({1})", (int)response.StatusCode, response.ReasonPhrase);
                }
            }
        }
    }

Movies class

public class Movies
    {
      public int page { get; set; }
      public int per_page { get; set; }
      public int total { get; set; }
      public int total_pages { get; set; }
      public List<MoviesData> data { get; set; }
    }

MoviesData class 

public class MoviesData
    {
        public string Title { get; set; }
        public int Year { get; set; }
        public string imdbID { get; set; } 
    }

The Abstract Modifier

The abstract modifier indicates that the thing being modified has a missing or incomplete implementation. The abstract modifier can be used with classes, methods, properties, indexers, and events.

The Virtual Keyword

The virtual keyword is used to modify a method, property, indexer, or event declaration and allow for it to be overridden in a derived class.

The Override Modifier

The override modifier is required to extend or modify the abstract or virtual implementation of an inherited method, property, indexer, or event.

Override Rules

• The overridden base method is a virtual, abstract, or override method. In other words, the overridden base method cannot be static or non-virtual.
• The overridden base method is not a sealed method.
• The override method and the overridden base method have the same return type and same signature.
• The override declaration and the overridden base method have the same declared accessibility (i.e public, internal etc).
• The override declaration does not specify type-parameter-constraints-clauses. Instead the constraints are inherited from the overridden base method.

Reference: https://docs.microsoft.com/

Code example

In following example override modifier is used to implement the abstract and extend virtual implementation of an inherited methods Print () and Display (), always it will call extended/ modified members.

   public abstract class OverrideParent
    {
        //Concreate implementation, child allowed to override 
        public virtual void Print()
        {
            Console.WriteLine("Parent virtual print");
        }
 
        //pure abstract member, child must override 
        public abstract void Display();
    }

    public class ChildOverride :OverrideParent
    {
        public override void Print()
        {
            Console.WriteLine("1st level print override");
        }
        public override void Display()
        {
            Console.WriteLine("1st level implementation");
        }
    }

    public class NestedChildOverride: ChildOverride
    {
        public override void Print()
        {
            Console.WriteLine("2nd level print override");
        }
        public override void Display()
        {
            Console.WriteLine("2nd level override/implementation");
        }
    }

Client implementation 

   //How it works?
    class Program
    {
        static void Main(string[] args)
        {
            OverrideParent ParentTypeChildImpn = new ChildOverride();
            ChildOverride ChildTypeChildImpn = new ChildOverride();
            ChildOverride ChildTypeNestedChldImpl = new NestedChildOverride();
            NestedChildOverride NestedChildTypeNestedImpl= new NestedChildOverride();
 
            //parent abstract type and child implementation
            ParentTypeChildImpn.Print();
            ParentTypeChildImpn.Display();
 
            //child type and child implementations
            ChildTypeChildImpn.Print();
            ChildTypeChildImpn.Display();
 
            //Child type and derived nested implementations
            ChildTypeNestedChldImpl.Print();
            ChildTypeNestedChldImpl.Display();
 
            //Nested child type and nested implementations
            NestedChildTypeNestedImpl.Print();
            NestedChildTypeNestedImpl.Display();
 
 
          }
    }

Output:

What is anonymous method in C#?

A method without a name is called as an anonymous method is, the delegate operator creates an anonymous method that can be converted to a delegate type.

What is use of anonymous methods in C#?

• You can use an anonymous method to create an anonymous function with unnamed inline code.
• C# 2.0 introduced the concept of anonymous methods to write unnamed inline statement blocks that can be executed in a delegate invocation.

How to create and use anonymous method?

An anonymous method behaves like a regular method and allows us to write inline code in place of explicitly named methods.

Code example

//declare delegate
delegate void displayFullName(string fname, string mName, string lName);
 
//instantiate delegate with anonymous method
displayFullName fullName = delegate (string fname, string mName, string lName) {
    Console.WriteLine("Full name: " + fname + " " + mName + " " + lName);
   };

 
//anonymous method with generic action delegate
Action<string, string, string> userFullName = delegate (string fname, string mName, string lName)
{
  Console.WriteLine("User full name: " + fname + " " + mName + " " + lName);
};