Handler Example

--> Android Handler Example Code

Handlers : Messages Between Threads
After multiple threads run concurrently, such as a main application thread and a background thread, there needs to be a way to communicate between them. Some examples are 

• A main thread serves time-critical information and passes messages to the background time-consuming thread to update. 

• A large computation completes and sends a message back to the calling thread with the result.

This can be accomplished with handlers, which are objects for sending messages between threads. Each handler is bound to a single thread, delivering messages to it and executing commands from it.
 

HandlerExampleActivity.java

package android.code.handler;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.widget.ImageView;

import android.widget.TextView;

public class HandlerExampleActivity extends Activity {

     

      private Handler hd;

      public int count=1;

      Boolean red = true,yellow=false,green = false;

      private ImageView light1,light2,light3;

   

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

       

        hd = new Handler();       

        final TextView tv = (TextView)findViewById(R.id.tv);

       

        light1 = (ImageView) findViewById(R.id.imageView1);

        light2 = (ImageView) findViewById(R.id.imageView2);

        light3 = (ImageView) findViewById(R.id.imageView3);

  

        Thread t = new Thread(new Runnable() {     

           

            public void run(){  

           

                  while (true){

                 

                        try{

                              Thread.sleep(2000);                                                                                        

                        }

                        catch(InterruptedException e)

                        { }

                                         

                        hd.post(new Runnable(){                        

                                                     

                              public void run(){  

                                   

                                    tv.setText("Thread Handler Running " + count++);

                                   

                                    if((red==true)&&(yellow==false)){

                                          light1.setImageResource(R.drawable.red);

                                          light2.setImageResource(R.drawable.off);

                                          light3.setImageResource(R.drawable.off);

                                          red = false;

                                          yellow = true;                                       

                                    }

                                    else if ((red==false)&&(yellow==true)){

                                          light1.setImageResource(R.drawable.off);

                                          light2.setImageResource(R.drawable.yellow);

                                          light3.setImageResource(R.drawable.off);

                                          red = false;

                                          yellow = false;                                      

                                    }

                                    else {

                                          light1.setImageResource(R.drawable.off);

                                          light2.setImageResource(R.drawable.off);

                                          light3.setImageResource(R.drawable.green);

                                          red = true;

                                          yellow = false;

                                         

                                    }

                              }

                        });

                                               

                  } // while

            }

        });

        t.start();

    }

}

main.xml

<?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:background="#FF6666"

    android:orientation="vertical" >

    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"

        android:layout_marginTop="10dp"

        android:text="Handler Example"

        android:textAppearance="?android:attr/textAppearanceLarge"

        android:textColor="#0000FF"

        android:textSize="30dp" />

    <TextView

        android:id="@+id/tv"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:layout_marginTop="20dp"

        android:background="#AA66CC"

        android:text="Thread Running"

        android:textColor="#000000"

        android:textSize="24dp" />

    <TextView

        android:id="@+id/textView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"

        android:layout_marginTop="10dp"

        android:text="Hanlder to change image"

        android:textAppearance="?android:attr/textAppearanceLarge"

        android:textColor="#669900" />

    <ImageView

        android:id="@+id/imageView1"

        android:layout_width="100dp"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"

        android:layout_marginTop="15dp"    

        android:src="@drawable/off" />

   

    <ImageView

        android:id="@+id/imageView2"

        android:layout_width="100dp"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"             

        android:src="@drawable/off" />

   

    <ImageView

        android:id="@+id/imageView3"

        android:layout_width="100dp"

        android:layout_height="wrap_content"

        android:layout_gravity="center_horizontal"           

        android:src="@drawable/off" />

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_marginLeft="20dp"

        android:layout_marginTop="50dp"

        android:text="main.xml"

        android:textAppearance="?android:attr/textAppearanceMedium"

        android:textColor="#0000FF"

        android:textSize="26dp" />

</LinearLayout>

Download Android Handler Example Code

More info

Android Thread Example
 

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http://androidcontrol.blogspot.com

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http://androidcontrol.blogspot.com/2012/01/beginning-android-training-android.html

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