Thread With Handlers - Android Example

Why we use handlers with thread :

When we install an application in android then it create a thread  for that application called MAIN UI Thread, All activities run inside that thread , By the android single thread model rule we can not access UI elements (bitmap , textview etc..) directly for another thread defined inside that activity.
 
 So if want to access Main UI Thread elements by another thread then we will use  handlers.

Thread With Handlers Example :

In this example  we are creating a thread and call webservice to get server response and after got the response,then do other functionality ( Save Data in database or show alert ,Redirect to another activity).

AndroidManifest.xml file

Add Internet Permission

<uses-permission android:name="android.permission.INTERNET"></uses-permission>

android_example_thread_handler.xml File

Create button with id : GetServerData

   
     <Button android:id="@+id/GetServerData"
           android:text="Click To Get Server Data"
           android:cursorVisible="true"
           android:clickable="true"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"  
           android:layout_gravity="center_horizontal"
     />
  

ThreadHandlerAndroidExample.java  File :

  public class ThreadHandlerAndroidExample extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.android_example_thread_handler);
        
        final Button GetServerData = (Button) findViewById(R.id.GetServerData);
        
        
        // On button click call this listener
        GetServerData.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                
                Toast.makeText(getBaseContext(),
                        "Please wait, connecting to server.",
                        Toast.LENGTH_SHORT).show();


                // Create Inner Thread Class
                Thread background = new Thread(new Runnable() {
                    
                    private final HttpClient Client = new DefaultHttpClient();
                    private String URL = "/media/webservice/getPage.php";
                    
                    // After call for background.start this run method call
                    public void run() {
                        try {

                            String SetServerString = "";
                            HttpGet httpget = new HttpGet(URL);
                            ResponseHandler<String> responseHandler = new BasicResponseHandler();
                            SetServerString = Client.execute(httpget, responseHandler);
                            threadMsg(SetServerString);

                        } catch (Throwable t) {
                            // just end the background thread
                            Log.i("Animation", "Thread  exception " + t);
                        }
                    }

                    private void threadMsg(String msg) {

                        if (!msg.equals(null) && !msg.equals("")) {
                            Message msgObj = handler.obtainMessage();
                            Bundle b = new Bundle();
                            b.putString("message", msg);
                            msgObj.setData(b);
                            handler.sendMessage(msgObj);
                        }
                    }

                    // Define the Handler that receives messages from the thread and update the progress
                    private final Handler handler = new Handler() {

                        public void handleMessage(Message msg) {
                            
                            String aResponse = msg.getData().getString("message");

                            if ((null != aResponse)) {

                                // ALERT MESSAGE
                                Toast.makeText(
                                        getBaseContext(),
                                        "Server Response: "+aResponse,
                                        Toast.LENGTH_SHORT).show();
                            }
                            else
                            {

                                    // ALERT MESSAGE
                                    Toast.makeText(
                                            getBaseContext(),
                                            "Not Got Response From Server.",
                                            Toast.LENGTH_SHORT).show();
                            }    

                        }
                    };

                });
                // Start Thread
                background.start();  //After call start method thread called run Method
            }
        });
        
    }

}

Explaination :

GetServerData Button click Listener :

GetServerData.setOnClickListener(new OnClickListener()

Show alert message:

    
        Toast.makeText(getBaseContext(),
                        "Please wait, connecting to server.",
                        Toast.LENGTH_SHORT).show();

Create new thread :

    
     Thread background = new Thread(new Runnable()  
       

Define http client :

    
     private final HttpClient Client = new DefaultHttpClient(); 
       

Define http url to send request :

    
     private String URL = "/media/webservice/getPage.php"; 
       

Create run() method :

Inside run method write code for http request to server and set server response in SetServerString String variable,  Call  threadMsg function and pass SetServerString.

    
         // After call for background.start this run method call
         public void run() {
                   try {

                            String SetServerString = "";
                            HttpGet httpget = new HttpGet(URL);
                            ResponseHandler<String> responseHandler = new BasicResponseHandler();
                            SetServerString = Client.execute(httpget, responseHandler);
                            threadMsg(SetServerString);

                        } catch (Throwable t) {
                            // just end the background thread
                            Log.i("ThreadHandler", "Thread  exception " + t);
                        }
                }
       

Create threadMsg Method :

    Use handler Object to set handler message and call sendMessage() method.
    After call on sendMessage() method  handler class handleMessage(str)  automatically call.

                 private void threadMsg(String msg) {
                      if (!msg.equals(null) && !msg.equals("")) {
                            Message msgObj = handler.obtainMessage();
                            Bundle b = new Bundle();
                            b.putString("message", msg);
                            msgObj.setData(b);
                            handler.sendMessage(msgObj);
                        }
                    }
   

Handler Inner Class :

         new Handler()                                          -  create new handler object
         msg.getData().getString("message")  -  Get sent message from sendMessage function.

          // Define the Handler that receives messages from the thread and update the progress
                     
            private final Handler handler = new Handler() {

                     // Create handleMessage function

                    public void handleMessage(Message msg) {
                            
                            String aResponse = msg.getData().getString("message");

                            if ((null != aResponse)) {

                                //ALERT MESSAGE
                                Toast.makeText(
                                        getBaseContext(),
                                        "Server Response: "+aResponse,
                                        Toast.LENGTH_SHORT).show();
                            }
                            else
                            {
                                    //ALERT MESSAGE
                                    Toast.makeText(
                                            getBaseContext(),
                                            "Not Got Response From Server.",
                                            Toast.LENGTH_SHORT).show();
                            }    

                        }
                    };