Android Example - Thread With Handlers

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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 = "http://androidexample.com/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 = "http://androidexample.com/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  threadMsgfunction 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();                   }                  }           }; OUTPUT :- Download full source code Fireandroids