Difference between revisions of "Android-app-using-Kotlin/C3/URL-Request/English"

Learning Objectives

• Pass the Foss and Language ids to the URL of Spoken Tutorial
• Parse the response JSON data
• Run the Kotlin App and
• Display the fetched data

System requirement

• Ubuntu Linux 16.04 operating system
• Android Studio version 3.x and
• Android Phone with minimum of Android OS version 4.03

Pre-requisites

• Java programming language and
• Android Studio

If not, then go through the relevant tutorials on this website.

Spoken Tutorial Server

• Spoken Tutorial project has a server which has an API made for a specific purpose.

• It helps to fetch the video tutorials of a FOSS in a particular language.

• Specific ids of a FOSS and language are passed to the server, to fetch the exact video.

API

• API means Application Programming Interface

• An API is the messenger that allows two software programs to communicate with each other

• It delivers the request to the provider and then delivers the response back to us

Spoken Tutorial URL Format:

https://spoken-tutorial.org/api/get_tutorials/fossID/languageID

In this URL, instead of variables fossID and languageID we have to pass the actual ids.

How to make a request to the URL?

• Google provides Volley library which makes requesting a URL easy and faster.

• Volley is an HTTP library that makes networking for Android Apps easier.

• It is an external library.

• We need to add to our Android studio project so that necessary files are downloaded.

Double click on build.gradle

Double-click on build.gradle within brackets Module:app

A new window opens.

implementation

'com.android.volley:volley:1.1.0'

We have now added the Volley library to our project.

implementation

'com.squareup.picasso:picasso:2.5.2'

This is to display the thumbnail of the spoken tutorial videos.

Click on it.

Click on it.

So let us add code to get Internet permission for the app.

Add the below code above the <application> tag.

Without this line of code, our App cannot request any information from the Internet.

val queue = Volley.newRequestQueue(this)

This will use the newRequestQueue method of volley library.

Here the URL is dynamic as we have to concatenate the FOSS and language ids received in intent.

So every time a different FOSS and language are selected, the URL will be different.

I’ll open Firefox web browser.

Type the following URL and press Enter.

Here, 10 specifies the FOSS id for Java and 22 specifies the language id for English.

For other browsers, it may look different.

Change the FOSS id to 26 and language id to 22

This URL gives the videos of Python in English.

Now let’s change the id to 26 and 18.

This URL returns empty data which indicates that there are no videos for this combination of ids.

JSON

• JSON stands for JavaScript Object Notation.

• JSON is easy to read and write.

• It is used to transmit data between a server and web application.

• It is an alternative to XML.

Write the below code after val url line, in the oncreate method as shown.

Select the appropriate option to quick fix the error.

Request.Method, url, Response.Listener and Response.ErrorListener.

Response.Listener specifies what to do when the response is received.

Response.ErrorListener specifies what to do when there is an error.

extractJsonData is a method which we will create later, to parse the JSON data that we have received.

Once we create the method, we will call it from the Response.Listener

This message “Contacting server…” indicates that still processing is going on.

Add the code in the next line as shown.

When the request is put in queue, the request is executed.

Search for a specific FOSS and language and press the Search button.

Assignment:

• Disconnect the Internet/Wifi.
• Now run the app and search for the FOSS and language.
• Observe the error output.

Parsing means extracting useful information.

The data in JSON is key-value pairs.

We will use the tutorial_name, video_id and tutorial_level fields present in the JSON data.

app => java => com.example.spoken.stsearch

Select New => Kotlin File/Class

Select New => Kotlin File/Class

Type a name as VideoItem and press OK.

A new file VideoItem.kt is created below SecondActivity.

Here we have created a class named as data class in Kotlin.

When data class is created, the getters and setters method are created while compiling.

So when we save the details of videos, we will make an object of this class for each video.

Here, video level specifies the basic, intermediate or advance level of spoken tutorials.

}

So write the code after the onCreate method:

In the method we take the response received as arguments.

As we know how the JSON data will look, we can start parsing it.

Write the code for it in extractJsonData method as shown.

Here we convert the response into JSONArray.

Now we know that inside this array there are many JSON objects of different videos.

Write the code as shown:

Declare a global ArrayList as shown above the onCreate method and inside the class.

In this ArrayList all the video data will be saved.

So that it will be accessible to both onCreate and extractJsonData methods.

In this ArrayList we have declared the type as VideoItem.

That means it will have objects of VideoItem class as data.

while loop is to iterate all the objects in JSON array:

In this loop we first obtain the json object in singleVideoJsonObject

Here we make an object of VideoItem and pass all the values from the JSON object.

The loop will extract data of all videos received and store it in our arraylist.

forEach method loops through all the elements of the array list.

The it variable in the println() statement points to one item in every loop.

//extractJsonData(response)

Un-comment the code, so that extractJsonData will be called from there.

When we take any one item from the array list, we get a object of VideoItem.

We can access the values for this object such as videoId, videoTitle, videoLevel.

So in this way JSON parsing is done.

Point to the output

Here we can see the output of println statement.

To find our output, search for video in search box.

Here we can see all the VideoItems shown one after the other.

Summary

• Pass the Foss and Language ids to the URL of Spoken Tutorial
• Parse the response JSON data
• Run the Kotlin App and
• Display the fetched data

About Spoken Tutorial project

About workshops

conducts workshops and gives certificates on passing online tests.

For more details, please write to us.

Forum for specific questions:

Acknowledgement

More information on this mission is available at

this link.

And this is Nirmala Venkat along with the Spoken Tutorial team from IIT Bombay, signing off.

Thanks for watching.