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Using Handler in Android Application


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Using Handler in Android Application

The class Handler can update the UI. A handle provides methods for receiving messages and for runnables. To use a handler you have to subclass it and overide handleMessage () to process messages. To process runables you can use the method post (); you only need one instance of a handler in your activity.

Your thread can post messages via the method sendMessage (Message msg) or sendEmptyMessage.

In this article I am going to explain how to create a handler in an Android application. In this example I will use the class Handler to update a ProgressBar in a background thread.

·         Start a new project named HandlerDemo.

·         Open res/values/strings.xml and add the following strings element in the resource tag:

    <string name="startProgress">startProgress</string>

·         Open res/layout/main.xml and insert the following code:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

       android:orientation="vertical" android:layout_width="fill_parent"

       android:layout_height="fill_parent">

       <ProgressBar android:id="@+id/progressBar1"

              style="?android:attr/progressBarStyleHorizontal"

              android:layout_width="match_parent"

              android:layout_height="wrap_content"

              android:indeterminate="false"

              android:max="10" android:padding="4dip">

       </ProgressBar>

       <Button android:text="Start Progress"

                     android:onClick="startProgress"

                     android:id="@+id/button1"

                     android:layout_width="wrap_content"

                     android:layout_height="wrap_content">

       </Button>

</LinearLayout>

 

·         Now open the Activity file and insert the following code:

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.view.View;

import android.widget.ProgressBar;

 

public class HandlerActivity extends Activity {

   

       private Handler handler;

       private ProgressBar progress;

 

       @Override

       public void onCreate(Bundle savedInstanceState) {

              super.onCreate(savedInstanceState);

              setContentView(R.layout.main);

              progress = (ProgressBar) findViewById(R.id.progressBar1);

              handler = new Handler();

       }

 

       public void startProgress(View view) {

             

              Runnable runnable = new Runnable() {

 

                     public void run() {

                           for (int i = 0; i <= 10; i++) {

                                  final int value = i;

                                  try {

                                         Thread.sleep(1000);

                                  } catch (InterruptedException e) {

                                         e.printStackTrace();

                                  }

                                  handler.post(new Runnable() {

                                        

                                         public void run() {

                                                progress.setProgress(value);

                                         }

                                  });

                            }

                     }

              };

              new Thread(runnable).start();

       }

}

·         Run the application.
The output looks like below:

Using Handler in Android Application

When you click on the Start Progress button, progress bar will start and looks like below:

Using Handler in Android Application


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