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Networking

We can data from a remote API using HTTP. Using REST API we can get and create data.

Permission

Android

To make network calls on Android you will need to have the INTERNET permission. On the Android project, add the following permission in the AndroidManifest.xml <uses-permission android:name="android.permission.INTERNET" />.

iOS

On iOS you will just need to make sure that the API is using https. If the url is http, you will need to add some configuration to the Info.plist file.

Performing a GET Request

Let's retrieve a random joke from the API url http://api.icndb.com/jokes/random. We use the GetStringAsync method of the HttpClient class as follows :

using (var client = new HttpClient()) {
    var content = await client.GetStringAsync("http://api.icndb.com/jokes/random");
    Console.WriteLine(content);
}

Performing a POST Request

To send data to the server you use the HTTP form data and send the parameters as form url encoded using the FormUrlEncodedContent class. The parameters will be sent as key/value pairs. We use the PostAsync method of the HttpClient class.

using (var client = new HttpClient())
{
    client.BaseAddress = new Uri("http://api.peruzal.com/");
    //Create a list of params
    var content = new FormUrlEncodedContent(new[]
    {
        //The parameters to post, in a key/value pair
        new KeyValuePair<string, string>("title", "Dawn of the Planet Earth"),
        new KeyValuePair<string, string>("category", "Sci-Fi")
    });

    //Make the network call to post
    var result = await client.PostAsync("/api/movie", content);
    string resultContent = await result.Content.ReadAsStringAsync();
    Console.WriteLine(resultContent);
}

Post JSON

Instead of sending the content as form url encoded, we can post the body of the content as JSON as follows:

var content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");
var result = await client.PostAsync(url, content).Result;

Posting form data

We can post form data using the FormUrlEncodedContent as follows:

var content = new FormUrlEncodedContent(new List<KeyValuePair<string, string>>()
{
    new KeyValuePair<string, string>("username", entryUsername.Text),
    new KeyValuePair<string,string>("password", entryPassword.Text)
}); 

var result = await client.PostAsync(url, content);

Send Headers

To send the headers, we add the headers as a key value pair in the DefaultRequestHeaders collection as follows :

private Task<string> fetchMovies(){
    var client = new HttpClient();
    //Add the header as a key value pair
    client.DefaultRequestHeaders.Add("X-Parse-Application-Id", "Value of header here");
    return client.GetStringAsync("https://parse.peruzal.com/parse/classes/Movie/");
}

Note

The header name is X-Parse-Application-Id and the value of the header is Value of header here.