title: Fragments - Unable to find button handler in activtity
body: <p>I am new to android. My login app was working perfectly, But when I converted my login user activity to fragment and getting below error:</p>
  
  <p>Error:</p>
  
  <pre><code>12-31 05:11:36.314 26809-26809/com.androidatc.customviewindrawer E/AndroidRuntime: java.lang.IllegalStateException: Could not find a method loginUser(View) in the activity class com.androidatc.customviewindrawer.MainActivity for onClick handler on view class android.widget.Button with id 'btnLogin'
  12-31 05:11:36.314 26809-26809/com.androidatc.customviewindrawer E/AndroidRuntime:     at android.view.View$1.onClick(View.java:4052)
  12-31 05:11:36.314 26809-26809/com.androidatc.customviewindrawer E/AndroidRuntime:     at android.view.View.performClick(View.java:4820)
  12-31 05:11:36.314 26809-26809/com.androidatc.customviewindrawer E/AndroidRuntime:     at android.view.View$PerformClick.run(View.java:20158)
  </code></pre>
  
  <p>Main.activity</p>
  
  <pre><code>package com.androidatc.customviewindrawer;
  
  import android.app.Activity;
  import android.content.Intent;
  import android.net.Uri;
  import android.support.v7.app.ActionBarActivity;
  import android.support.v7.app.ActionBar;
  import android.app.Fragment;
  //import android.support.v4.app.Fragment;
  //import android.support.v4.app.FragmentManager;
  import android.app.FragmentManager;
  
  import android.os.Bundle;
  import android.view.LayoutInflater;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  import android.view.ViewGroup;
  import android.support.v4.widget.DrawerLayout;
  import android.widget.Toast;
  
  
  public class MainActivity extends ActionBarActivity
          implements NavigationDrawerFragment.NavigationDrawerCallbacks,
          SearchCatFragment.OnFragmentInteractionListener,
          AndroidBarcodeQrExample.OnFragmentInteractionListener,
          BarCodeFrag.OnFragmentInteractionListener,
          LoginFrag.OnFragmentInteractionListener,
          MainViewFragment.OnFragmentInteractionListener {
  
      /**
       * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
       */
      private NavigationDrawerFragment mNavigationDrawerFragment;
  
      /**
       * Used to store the last screen title. For use in {@link #restoreActionBar()}.
       */
      private CharSequence mTitle;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          mNavigationDrawerFragment = (NavigationDrawerFragment)
                  getFragmentManager().findFragmentById(R.id.navigation_drawer);
          mTitle = getTitle();
  
          // Set up the drawer.
          mNavigationDrawerFragment.setUp(
                  R.id.navigation_drawer,
                  (DrawerLayout) findViewById(R.id.drawer_layout));
      }
  
      @Override
      public void onNavigationDrawerItemSelected(int position) {
          // update the main content by replacing fragments
          FragmentManager fragmentManager = getFragmentManager();
          fragmentManager.beginTransaction()
                  .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
                  .commit();
      }
  
  
  
      public void onActivityResult(int requestCode, int resultCode, Intent intent) {
          if (requestCode == 0) {
              if (resultCode == RESULT_OK) {
                  String contents = intent.getStringExtra("SCAN_RESULT");
                  String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
                  Toast toast = Toast.makeText(this, "Content:" + contents + " Format:" + format, Toast.LENGTH_LONG);
                  toast.show();
              }
          }
      }
  
      public void onSectionAttached(int number) {
          switch (number) {
              case 1:
                  mTitle = getString(R.string.title_section1);
                  break;
              case 2:
                  mTitle = getString(R.string.title_section2);
                  break;
              case 3:
                  mTitle = getString(R.string.title_section3);
                  break;
              case 4:
                  mTitle = getString(R.string.title_section4);
                  break;
              case 5:
                  mTitle = getString(R.string.title_section5);
                  break;
          }
      }
  
      public void restoreActionBar() {
          ActionBar actionBar = getSupportActionBar();
          actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
          actionBar.setDisplayShowTitleEnabled(true);
          actionBar.setTitle(mTitle);
      }
  
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          if (!mNavigationDrawerFragment.isDrawerOpen()) {
              // Only show items in the action bar relevant to this screen
              // if the drawer is not showing. Otherwise, let the drawer
              // decide what to show in the action bar.
              getMenuInflater().inflate(R.menu.menu_main, menu);
              restoreActionBar();
              return true;
          }
          return super.onCreateOptionsMenu(menu);
      }
  
      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
          // Handle action bar item clicks here. The action bar will
          // automatically handle clicks on the Home/Up button, so long
          // as you specify a parent activity in AndroidManifest.xml.
          int id = item.getItemId();
  
          //noinspection SimplifiableIfStatement
          if (id == R.id.action_settings) {
              return true;
          }
  
          return super.onOptionsItemSelected(item);
      }
  
  
  
      @Override
      public void onFragmentInteraction(Uri uri) {
  
      }
  
      /**
       * A placeholder fragment containing a simple view.
       */
      public static class PlaceholderFragment extends Fragment {
          /**
           * The fragment argument representing the section number for this
           * fragment.
           */
          private static final String ARG_SECTION_NUMBER = "section_number";
  
          /**
           * Returns a new instance of this fragment for the given section
           * number.
           */
          public static PlaceholderFragment newInstance(int sectionNumber) {
              PlaceholderFragment fragment = new PlaceholderFragment();
              Bundle args = new Bundle();
              args.putInt(ARG_SECTION_NUMBER, sectionNumber);
              fragment.setArguments(args);
              return fragment;
          }
  
          public PlaceholderFragment() {
          }
  
          @Override
          public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                   Bundle savedInstanceState) {
              View rootView = inflater.inflate(R.layout.fragment_main, container, false);
              return rootView;
          }
  
          @Override
          public void onAttach(Activity activity) {
              super.onAttach(activity);
              ((MainActivity) activity).onSectionAttached(
                      getArguments().getInt(ARG_SECTION_NUMBER));
          }
      }
  
  }
  </code></pre>
  
  <p>LoginFrag.java</p>
  
  <pre><code>package com.androidatc.customviewindrawer;
  
  import android.app.Activity;
  import android.app.Fragment;
  import android.app.ProgressDialog;
  import android.content.Intent;
  import android.net.Uri;
  import android.os.Bundle;
  import android.view.LayoutInflater;
  import android.view.View;
  import android.view.ViewGroup;
  import android.widget.EditText;
  import android.widget.TextView;
  import android.widget.Toast;
  
  import com.loopj.android.http.AsyncHttpClient;
  import com.loopj.android.http.AsyncHttpResponseHandler;
  import com.loopj.android.http.RequestParams;
  
  import cz.msebera.android.httpclient.Header;
  
  /**
   * 
   * Login Activity Class 
   *
   */
  public class LoginFrag extends Fragment {
      // Progress Dialog Object
      ProgressDialog prgDialog;
      // Error Msg TextView Object
      TextView errorMsg;
      // Email Edit View Object
      EditText emailET;
      // Passwprd Edit View Object
      EditText pwdET;
      @Override
  
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
                               Bundle savedInstanceState) {
          // Inflate the layout for this fragment
          View rootView = inflater.inflate(R.layout.login, container, false);
  
          errorMsg = (TextView) rootView.findViewById(R.id.login_error);
          // Find Email Edit View control by ID
          emailET = (EditText) rootView.findViewById(R.id.loginEmail);
          // Find Password Edit View control by ID
          pwdET = (EditText) rootView.findViewById(R.id.loginPassword);
          // Instantiate Progress Dialog object
          prgDialog = new ProgressDialog(this.getActivity());
          // Set Progress Dialog Text
          prgDialog.setMessage("Please wait...");
          // Set Cancelable as False
          prgDialog.setCancelable(false);
  
          return rootView;
      }
      /**
       * Method gets triggered when Login button is clicked
       * 
       * @param view
       */
      public void loginUser(View view){
          // Get Email Edit View Value
          String email = emailET.getText().toString();
          // Get Password Edit View Value
          String password = pwdET.getText().toString();
          // Instantiate Http Request Param Object
          RequestParams params = new RequestParams();
  
                  // Put Http parameter username with value of Email Edit View control
                  params.put("username", email);
                  // Put Http parameter password with value of Password Edit Value control
                  params.put("password", password);
  
          final int DEFAULT_TIMEOUT = 200000 * 1000000000;
  
          // Make RESTful webservice call using AsyncHttpClient object
          AsyncHttpClient client = new AsyncHttpClient();
          client.setTimeout(DEFAULT_TIMEOUT);
  
          client.get("http://abc/ilsdi.pl?service=AuthenticatePatron", params ,new AsyncHttpResponseHandler() {
  
  
              public void onSuccess(int i, Header[] headers, byte[] bytes) {
  
                  Toast.makeText(getActivity().getApplicationContext(), "XML File: " + headers, Toast.LENGTH_LONG).show();
  
  
              }
  
              @Override
              public void onFailure(int i, Header[] headers, byte[] bytes, Throwable throwable) {
                  Toast.makeText(getActivity().getApplicationContext(), "Status code :" + i + "errmsg : " + throwable.getMessage(), Toast.LENGTH_LONG).show();
                  Toast.makeText(getActivity().getApplicationContext(), "Unexpected Error occcured! [Most common Error: Device might not be connected to Internet or remote server is not up and running]", Toast.LENGTH_LONG).show();
  
              }
  
  
              public void onSuccess(String response) {
                  // Hide Progress Dialog
                  prgDialog.hide();
                  Toast.makeText(getActivity().getApplicationContext(), "XML File: " + response, Toast.LENGTH_LONG).show();
  
                      Toast.makeText(getActivity().getApplicationContext(), "You are successfully logged in!", Toast.LENGTH_LONG).show();
                      navigatetoHomeActivity();
                      //e.printStackTrace();
  
              }
              // When the response returned by REST has Http response code other than '200'
  
              public void onFailure(int statusCode, Throwable error,
                                    String content) {
                  // Hide Progress Dialog
                  prgDialog.hide();
                  // When Http response code is '404'
                  if(statusCode == 404){
                      Toast.makeText(getActivity().getApplicationContext(), "Requested resource not found", Toast.LENGTH_LONG).show();
                  }
                  // When Http response code is '500'
                  else if(statusCode == 500){
                      Toast.makeText(getActivity().getApplicationContext(), "Something went wrong at server end", Toast.LENGTH_LONG).show();
                  }
                  // When Http response code other than 404, 500
                  else{
                      Toast.makeText(getActivity().getApplicationContext(), "Status code :" + statusCode + "errmsg : " + error.getMessage(), Toast.LENGTH_LONG).show();
                      Toast.makeText(getActivity().getApplicationContext(), "Unexpected Error occcured! [Most common Error: Device might not be connected to Internet or remote server is not up and running]", Toast.LENGTH_LONG).show();
                  }
              }
          });
  
  
  
      }
  
      /**
       * Method which navigates from Login Activity to Home Activity
       */
      public void navigatetoHomeActivity(){
          Intent homeIntent = new Intent(getActivity().getApplicationContext(),HomeActivity.class);
          homeIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
          startActivity(homeIntent);
      }
  
      public interface OnFragmentInteractionListener {
          // TODO: Update argument type and name
          public void onFragmentInteraction(Uri uri);
      }
  
  
  
  
  
  }
  </code></pre>
  
  <p>login.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent" &gt;
  
      &lt;LinearLayout
          android:layout_width="fill_parent"
          android:layout_height="wrap_content"
          android:orientation="vertical"
          android:padding="10dip" &gt;
  
          &lt;TextView
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:layout_marginBottom="10dip"
              android:text="@string/login_title"
              android:textSize="25sp"
              android:textStyle="bold" /&gt;
  
          &lt;EditText
              android:id="@+id/loginEmail"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:hint="Enter your User ID"
              android:inputType="textEmailAddress" /&gt;
  
          &lt;TextView
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:layout_marginTop="15dip"
              android:text="@string/pwd" /&gt;
  
          &lt;EditText
              android:id="@+id/loginPassword"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:hint="Enter Password"
              android:inputType="textPassword" /&gt;
  
          &lt;TextView
              android:id="@+id/login_error"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:padding="10dip"
              android:textColor="#e30000"
              android:textStyle="bold" /&gt;
  
          &lt;Button
              android:id="@+id/btnLogin"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:layout_marginTop="20dip"
              android:background="#ff6347"
              android:onClick="loginUser"
              android:text="Login"
              android:textColor="#fff" /&gt;
  
          &lt;Button
              android:id="@+id/btnLinkToRegisterScreen"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:layout_marginTop="40dip"
              android:background="@null"
              android:onClick="navigatetoRegisterActivity"
              android:text="Signup"
              android:textColor="#228b22"
              android:textStyle="bold" /&gt;
      &lt;/LinearLayout&gt;
  
  &lt;/ScrollView&gt;
  </code></pre>
  
  <p>Appreciate any suggestions. Thanks</p>