Create and Execute Asynctask in Android. aysnctask in android.

useful resource : https://youtu.be/2bQCyarmFLA

Asynctask is bound to the Activity, so due to this , It is used ONLY by the Activity which creates.

(Jo activity isse create krti h sirf vahi isse use krti h )

In most cases , it is created as a inner class inside a Activity code.

Asynctask has a main method called doinBackground() , inside which we write the code to be executed in the background.

doinBackground also has 3 sub methods that get called at different stages of its execution.

OnPreExecute() - gets executed before the doinbackground() method starts

OnProgressUpdate - keeps on executing parallel with doinbacground() method.

OnPostExecute() - gets executed after the doinBackground() gets over.

Create a asynctask and execute it below :

full code :

(You can use on asynctask object only once)

public class MainActivity extends AppCompatActivity {

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

    public void StartMethod(View view) {
        
        //Create a object of Asynctask class and apply the
        // execute() method passing the execute method the parameters.

        NestedClass nestedClass1 = new NestedClass();
        nestedClass1.execute("Deepesh","Kiran","Rohan");

        NestedClass nestedClass2 = new NestedClass();
        nestedClass2.execute("A","B","C");
    }

   //Asynctask class
    class NestedClass extends AsyncTask<String,String,String>{
        @Override
        protected String doInBackground(String... strings) {

            for (String name: strings) {

                Log.d("Keyy", " Threadname :" + Thread.currentThread().getName()+ " ArryNames :"+ name );
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return null;
        }
    }

[

INPUT parameter - same as the parameters taken by the doinBackground()

RESULT parameter- is the result type of the doinBckground().

]

Step 1] Create a inner class that extends to Asynctask class

Step2] Pass the Asysnctask  "< >" the 3 parameter types for INPUT , PROGRESS, RESULT.

Input data type is for doInBackground() , progress data type is for OnProgressUpdate() and result data type is for onPostExecute(). The result of doInBackground() is send to onPostExecute()

Step3] Implement its doinbackground() methods and pass it the Input parameter that you'll need to take from the users (if any) .

step4 ] Write the code inside the method that you want to run in the backgorund thread

step5] Now , to execute the Asynctask , create a object of the class whihc extended the Asynctask.

and apply the execute() method on the object , pass the parameters required inside the execute() method.

You can execute the Asynctask multiple times by creating multiple objects of DIFFERENT NAMES, whihc will run SEQUENCIALLY one after another.

EXAMPLE 2 : 

static class NestedClass extends AsyncTask<String,String,String>{
    @Override
    protected String doInBackground(String... strings) {
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);
    }

    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
}

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OnPreExecute() - runs on the Main thread or on the thread that STARTS the Asynctask.

OnProgressUpdate  & OnPostexecute - runs on UI thread.

doinBackground() - runs on the BACKGROUND thread.

YOU CANNOT ACESS THE MAIN / UI THREAD FROM ASYNCTASK DIRECLTY

1] Asynctask doesnt survive Orientation changes, hence we use AsynctaskLoader 

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How to update UI from asynctask :

https://code8808.blogspot.com/2020/07/update-ui-from-asynctask-using.html

Problems with Asynctask :

https://youtu.be/hcUIhSVYKiI