Android Handler – Update ProgressBar

Android Handler and ProgressBar Update Tutorial and Examples

In this tutorial we want to see how to post updates from a background thread to the user interface thread using a Handler.

We click a button and simulate doing heavy work in the background. Meanwhile we are able to update our progressbar as the work continues.

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(a). MainActivity.java

This is the main activity. We derive from the AppCompatActivity. One of the imports we add is the Handler from the android.os package.

...
import android.os.Handler;
...

We will maintain three instance fields:

1. Handler – a class defined in the android.os package through which we can send and process Message and Runnable objects associated with a thread’s MessageQueue.
2. ProgressBar – a widget that allows us to show progress.
3. Button – an action button.

Here’s the full code:

package info.camposha.mrhandler;

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;

public class MainActivity extends AppCompatActivity {

    private Handler mHandler;
    private ProgressBar mProgressBar;
    private Button mStartButton;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mHandler = new Handler();
        mProgressBar = findViewById(R.id.mProgressBar);
        mStartButton = findViewById(R.id.startBtn);
        mStartButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                performStuff();
            }
        });
    }
    private void performStuff() {
        //Simulate Heavy task in background thread
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i <= 30; i++) {
                    final int currentProgressCount = i;
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                //Post updates to the User Interface
                    mHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            mProgressBar.setProgress(currentProgressCount);
                        }
                    });
                }
            }
        }).start();
    }
}

(b). activity_main.xml

This is the main activity layout. At the root we have a LinearLayout. This element allows us to arrange it’s children linearly either horizontally or vertically. We also have TextView to display the header text of our app. Also we have a progressbar to display progress. We have also a button that when clicked will start the thread to perform our work in the background thread.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    android_layout_width="match_parent"
    android_layout_height="match_parent"
    
    android_gravity="center"
    android_orientation="vertical"
    tools_context=".MainActivity">

    <TextView
        android_id="@+id/headerLabel"
        android_layout_width="wrap_content"
        android_layout_height="wrap_content"
        android_layout_alignParentTop="true"
        android_layout_centerHorizontal="true"
        android_fontFamily="casual"
        android_text="Handler ProgressBar"
        android_textAllCaps="true"
        android_textSize="24sp"
        android_textStyle="bold" />

    <ProgressBar
        android_id="@+id/mProgressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android_layout_width="match_parent"
        android_layout_height="wrap_content"
        android_layout_margin="10dp"
        android_indeterminate="false"
        android_max="10" />

    <Button
        android_id="@+id/startBtn"
        android_layout_width="wrap_content"
        android_layout_height="wrap_content"
        android_text="Start" />
</LinearLayout>