title: Correct method to implement onclick button in android
body: <p>I am doing a login page and have the following codes as below. The moment I open up this codes </p>
  
  <pre><code> // Login button clicked
                 // ok = (Button)findViewById(R.id.btn_login);
                 // ok.setOnClickListener((android.view.View.OnClickListener) this);
  </code></pre>
  
  <p>My app crashes. I look throught most are using this approach public class MainActivity extends ActionBarActivity implements OnClickListener so I followed. What is the correct method to enable when on click the button login to call post the data?</p>
  
  <pre><code>import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.http.HttpResponse;
  import org.apache.http.NameValuePair;
  import org.apache.http.client.ClientProtocolException;
  import org.apache.http.client.HttpClient;
  import org.apache.http.client.entity.UrlEncodedFormEntity;
  import org.apache.http.client.methods.HttpPost;
  import org.apache.http.impl.client.DefaultHttpClient;
  import org.apache.http.message.BasicNameValuePair;
  
  import android.support.v7.app.ActionBarActivity;
  import android.content.DialogInterface;
  import android.content.DialogInterface.OnClickListener;
  import android.os.Bundle;
  import android.util.Log;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.TextView;
  
  public class MainActivity extends ActionBarActivity implements OnClickListener {
  
      Button ok,back,exit;
       TextView result;
  
          /** Called when the activity is first created. */
          @Override
          public void onCreate(Bundle savedInstanceState) {
              super.onCreate(savedInstanceState);
              setContentView(R.layout.login);
  
              // Login button clicked
             // ok = (Button)findViewById(R.id.btn_login);
             // ok.setOnClickListener((android.view.View.OnClickListener) this);
  
              result = (TextView)findViewById(R.id.lbl_result);
  
          }
  
          public void postLoginData() {
              // Create a new HttpClient and Post Header
              HttpClient httpclient = new DefaultHttpClient();
  
              /* login.php returns true if username and password is equal to saranga */
              HttpPost httppost = new HttpPost("http://www.sencide.com/blog/login.php");
  
              try {
                  // Add user name and password
               EditText uname = (EditText)findViewById(R.id.txt_username);
               String username = uname.getText().toString();
  
               EditText pword = (EditText)findViewById(R.id.txt_password);
               String password = pword.getText().toString();
  
                  List&lt;NameValuePair&gt; nameValuePairs = new ArrayList&lt;NameValuePair&gt;(2);
                  nameValuePairs.add(new BasicNameValuePair("username", username));
                  nameValuePairs.add(new BasicNameValuePair("password", password));
                  httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
  
                  // Execute HTTP Post Request
                  Log.w("SENCIDE", "Execute HTTP Post Request");
                  HttpResponse response = httpclient.execute(httppost);
  
                  String str = inputStreamToString(response.getEntity().getContent()).toString();
                  Log.w("SENCIDE", str);
  
                  if(str.toString().equalsIgnoreCase("true"))
                  {
                   Log.w("SENCIDE", "TRUE");
                   result.setText("Login successful");   
                  }else
                  {
                   Log.w("SENCIDE", "FALSE");
                   result.setText(str);             
                  }
  
              } catch (ClientProtocolException e) {
               e.printStackTrace();
              } catch (IOException e) {
               e.printStackTrace();
              }
          } 
  
          private StringBuilder inputStreamToString(InputStream is) {
           String line = "";
           StringBuilder total = new StringBuilder();
           // Wrap a BufferedReader around the InputStream
           BufferedReader rd = new BufferedReader(new InputStreamReader(is));
           // Read response until the end
           try {
            while ((line = rd.readLine()) != null) { 
              total.append(line); 
            }
           } catch (IOException e) {
            e.printStackTrace();
           }
           // Return full string
           return total;
          }
  
          public void onClick(View view) {
            if(view == ok){
              postLoginData();
            }
          }
  
          @Override
          public void onClick(DialogInterface dialog, int which) {
              // TODO Auto-generated method stub
  
          }
  
  
  }
  </code></pre>
  
  <p>Below are some error I got when I try to run my application with onclick event</p>
  
  <pre><code>09-30 01:58:01.075: E/AndroidRuntime(1342): FATAL EXCEPTION: main
  09-30 01:58:01.075: E/AndroidRuntime(1342): Process: com.example.guard1, PID: 1342
  09-30 01:58:01.075: E/AndroidRuntime(1342): android.os.NetworkOnMainThreadException
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at java.net.InetAddress.getAllByName(InetAddress.java:214)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at com.example.guard1.MainActivity.postLoginData(MainActivity.java:72)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at com.example.guard1.MainActivity.onClick(MainActivity.java:113)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.view.View.performClick(View.java:4438)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.view.View$PerformClick.run(View.java:18422)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.os.Handler.handleCallback(Handler.java:733)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.os.Handler.dispatchMessage(Handler.java:95)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.os.Looper.loop(Looper.java:136)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at android.app.ActivityThread.main(ActivityThread.java:5017)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at java.lang.reflect.Method.invokeNative(Native Method)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at java.lang.reflect.Method.invoke(Method.java:515)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
  09-30 01:58:01.075: E/AndroidRuntime(1342):     at dalvik.system.NativeStart.main(Native Method)
  </code></pre>