Async Task in Android

Async task in Android

Scenario: 

You have a Mobile application where in you have selected any of the option which should fetch some data from the server or from web. 

So to fetch that data there will be a request from your app to the server/web. 

That request will be handling in the background by using another thread without distrubing your app. So this task is called Async task.

Mainly this Async task will be used to handle multithreading tasks.

How to implement

To implement Async task , we should extend our class with Asynctask.

This AsyncTask class will be having overridden methods which is below.

• onPreExecute()
• doInBackground()
• onProgressUpdate()
• onPostExecute()

How to implement these methods in AsyncTask class

onPreExecute(): This method will be used before starting of request to the server, UI thread will take care of this method execution.

doInBackground(params):You have to pass parameters to this method , where your request will be executing in the background.

onProgressUpdate(progress): progress of your request to the server

onPostExecute(result): The result from the server of your request.

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Note:Mostly this Async task we have to use when there is minimal time like below five seconds can take time to interact with server/web to get the response to the app.So that we can minimize the waiting time of the user.If waiting time is more we can go for other concept called executor.

Example.

Create activity_main.xml for UI

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >

    <EditText android:id="@+id/num1"        android:layout_width="270dp"        android:layout_height="wrap_content"        android:hint="Number 1"        />

    <EditText android:id="@+id/num2"        android:layout_width="270dp"        android:layout_height="wrap_content"        android:hint="num2"        />
     <Button android:id="@+id/add"        android:layout_width="270dp"        android:layout_height="wrap_content"        android:text="submit"/>


</LinearLayout>

MainActitivity.java

package com.example.sample1;

import androidx.appcompat.app.AppCompatActivity;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    EditText num1,num2;
    Button mybutton;
    String strurl="http://www.telusko.com/addition.html?t1=3&t2=2";
    String result="";

    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        num1 = findViewById(R.id.num1);
        num2 = findViewById(R.id.num2);


        mybutton = findViewById(R.id.add);
        mybutton.setOnClickListener(new View.OnClickListener() {
            @Override            public void onClick(View v) {
                int i=Integer.parseInt(num1.getText().toString());
                int j=Integer.parseInt(num2.getText().toString());
                strurl="http://www.telusko.com/addition.html?t1="+i+"&t2="+j;
                new AddTask().execute();


            }
        });
    }

    public class AddTask extends AsyncTask<String,String,String>
    {
        @Override        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override        protected void onPostExecute(String s) {
            //super.onPostExecute(s);            Toast.makeText(MainActivity.this,"This is the result"+result,Toast.LENGTH_LONG).show();
        }

        @Override        protected String doInBackground(String... strings) {
            try {
                URL url=new URL(strurl);
                HttpURLConnection con=(HttpURLConnection) url.openConnection();
                con.setRequestMethod("GET");
                con.connect();
                BufferedReader bf=new BufferedReader(new InputStreamReader(con.getInputStream()));
                String value=bf.readLine();
                System.out.println(value);
                result=value;


            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
    }
}

output: