Category: C# & .NET

Posted on by — 1 Comment

Consume php backend nested array on a C# Application – Json.NET

Lets assume you got a MYSQL database that contains data for your application and you want to consume this information on a C# Application in order to handle it on a client.

For the sake of this example the following table will be parsed

As depicted the following information is returned from the api:

  • the state of the response (succeeded or not)
  • a message that will show the response result
  • the actual result that in this case is a list of trips

Each trip contains id, fromlocation, tolocation, date and time properties that have to be returned to the application.

The php code that was used to create the data from the database is the following:

         $trips =array();
         while ( $row = $stmt->fetch() ) {         
         $obj["id"]= $row['id'];
         $obj['fromlocation']= $row['fromlocation'];
         $obj['tolocation'] = $row['tolocation'];       
         $obj['date']= $row['date'];
         $obj['time'] = $row['time'];         
         array_push($trips,$obj);
         }

         $response["success"] = 1;
         $response["message"] = "Trips returned successfully!";
         $response["trips"] = $trips;
         die(json_encode($response));

So in order to parse this json result we will need a plugin like Newtonsoft.Json

The class that will be used to encapsulate the response would be the following:

public class GetTrips
    {
        [JsonProperty("success")]
        public int Success { get; set; }

        [JsonProperty("message")]
        public string Message { get; set; }
        [JsonProperty("trips")]
        public Trip[]  Trips { get; set; }

       
        public class Trip
        {
            [JsonProperty("id")]
            public string Id { get; set; }
            [JsonProperty("fromlocation")]
            public string FromLocation { get; set; }
            [JsonProperty("tolocation")]
            public string ToLocation { get; set; }
            [JsonProperty("date")]
            public string Date { get; set; }
            [JsonProperty("time")]
            public string Time { get; set; }
        }

    }

And then we will consume the json response with the following code in C#. In this example data from the API came from a POST request on a web Form.

public async TaskGetTripsAsync(string username,string password)
        {
            try
            {
                var keyValues = new Liststring, string>>
                {
                    new KeyValuePair("username",username),
                    new KeyValuePair("password",password)
                };

                var request = new HttpRequestMessage(HttpMethod.Post, Url);
                request.Content = new FormUrlEncodedContent(keyValues);

                var client = new HttpClient();
                var result = await client.SendAsync(request);
                var content = await result.Content.ReadAsStringAsync();
                var tripsResult = JsonConvert.DeserializeObject (content);
                return tripsResult;
            }
            catch (Exception)
            {
                return null;
            }
        }

Posted on by — Leave a comment

Send signals between Mainpage.xaml.cs and Viewmodel – Xamarin.Forms

In a recent application I wanted to inform a Listview with a specific ItemTemplate to update its data source on back button with a synchronous data fetching mechanism(so this was not automatic).

So the goal was to send a “signal” to my Viewmodel when the page was loaded to perform an action. This can be done using MessageCenter with Xamarin.Forms.

The solution was to send an update signal every time OnAppearing() method of the MainPage.xaml was hit and inform the ViewModel to perfom an action.

 protected override void OnAppearing()
        {
            MessagingCenter.Send<nameofapp.App>((nameofapp.App)Xamarin.Forms.Application.Current, "update");
        }

Then perform action on MainPageViewModel

public MainPageViewModel()
        {
           
            MessagingCenter.Subscribe<nameofapp.App>((nameofapp.App)Application.Current, "update", (sender) => {
                var result = viewmodel.fetchData();
            });


        }

 

 

Posted on by — 1 Comment

Find the Nth Fibonacci Number – C# Code

The Fibonacci sequence begins with Fibonacci(0) = 0  and Fibonacci(1)=1  as its respective first and second terms. After these first two elements, each subsequent element is equal to the sum of the previous two elements.

Here is the basic information you need to calculate Fibonacci(n):

  • Fibonacci(0) = 0
  • Fibonacci(1) = 1
  • Fibonacci(n) = Fibonacci(n-1) + Fibonacci(n-2)

Task
Given n, complete the fibonacci function so it returns Fibonacci(n).

Input Format

Nth number

Output Format

Fibonacci() Nth number.

Sample Input

3

Sample Output

2

Explanation

Consider the Fibonacci sequence:

We want to know the value of Fibonacci(3). If we look at the sequence above,Fibonacci(3)  evaluates to 2. Thus, we print 2 as our answer.

 

  public static int Fibonacci(int n)
        {
            if (n == 0) return 0;
            else if (n == 1) return 1;
            else
            {
                return Fibonacci(n - 1) + Fibonacci(n - 2);
            }
        }
Posted on by — 1 Comment

Array Left Rotation by D – C# Code

A left rotation operation on an array of size n shifts each of the array’s elements 1 unit to the left. For example, if 2 left rotations are performed on array [1,2,3,4,5], then the array would become  [3,4,5,1,2].

Given an array of  n integers and a number, d , perform d left rotations on the array. Then print the updated array as a single line of space-separated integers.

Input Format

The first line contains two space-separated integers denoting the respective values of  (the number of integers) and  (the number of left rotations you must perform).
The second line contains  space-separated integers describing the respective elements of the array’s initial state.

Output Format

Print a single line of  space-separated integers denoting the final state of the array after performing  left rotations.

Sample Input

5 4
1 2 3 4 5

Sample Output

5 1 2 3 4

 
Explanation

 

Code

 static int[] LeftRotationByD(int[] a,int k)
        {
            int[] b = new int[a.Length];

            int index;
            int length = a.Length;
            int place;


            for (int i = 0; i < length; i++)
            {
                index = i - k;
                place = length + index;
                if (index >= 0)
                {
                    b[index] = a[i];
                }
                else
                {
                    b[place] = a[i];
                }
            }
            return b;

        }

 

We can see the results for 1 and 4 rotations as follows: