Handler in Android. Handler PostDelayed() method & Post() in Android.

The Handler runs on the Main thread.

It doesnt create a seperate thread and run  on worker thread.

The Handler has 2 main methods- Postdelayed() and Post()

---------------------------------------------------------------------------------------------------------------------------

1] Handler.PostDelayed()

This method is used when we want to run a code on the Main/UI thread after a certain amount of time.

if you use this method , you have to provide a Time after whiihc the code gets executed.

Step 1] Create a Handler Object and Implement the Postdelayed() method on it.

public class MainActivity extends AppCompatActivity {

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

        Button button = findViewById(R.id.Button1);
        button.setOnClickListener(listener);
    }

    View.OnClickListener listener = new View.OnClickListener() {
        @Override
        public void onClick(View view) {

          Handler handler = new Handler();
          handler.postDelayed(new Runnable() {
              @Override
              public void run() {

                  TextView textView = findViewById(R.id.textview1);
                  textView.setText("Hello World !");

              }
          },5000);
        }
    };

}

step 2] The Postdelayed() method takes two agruments , A runnable object and the Time after whihc the code must be executed.

--------------------------------------------------------------------------------------------------------------------------

2] Handler.Post() 

This method takes only one Argument i.e a Runnable object.

This method adds the Code into the WorkQue and executes it immitiately on its Turn.

-----------------------------------------------------------------------------------

Useful video which explains both the Methods :

https://youtu.be/BVkT-lrDgm0