Notification example on Android's site -

so i'm quite new android , i'm working through of example code off android's site. 1 i'm looking @ called notifying user: http://developer.android.com/training/notify-user/index.html.

the example pretty simple, user enters in time in seconds , message, , timer set in background. once time runs out, user notified.

so here copy of activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent" >      <textview         android:id="@+id/seconds_view"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignparenttop="true"         android:layout_centerhorizontal="true"         android:layout_margintop="32dp"         android:textappearance="?android:attr/textappearancemedium"         android:text="@string/ping_text" />      <edittext         android:id="@+id/edit_seconds"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_below="@+id/seconds_view"         android:layout_centerhorizontal="true"         android:layout_margintop="15dp"         android:ems="10"         android:text="@string/seconds_default"         android:inputtype="numbersigned">          <requestfocus />     </edittext>      <textview         android:id="@+id/reminder_view"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_below="@+id/edit_seconds"         android:layout_centerhorizontal="true"         android:layout_margintop="40dp"         android:textappearance="?android:attr/textappearancemedium"         android:text="@string/reminder_label" />      <edittext         android:id="@+id/edit_reminder"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignleft="@+id/edit_seconds"         android:layout_below="@+id/reminder_view"         android:layout_margintop="15dp"         android:ems="10"         android:text="@string/reminder_text"         android:inputtype="textmultiline" />      <button         android:id="@+id/ping_button"         style="?android:attr/buttonstylesmall"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_below="@+id/edit_reminder"         android:layout_centerhorizontal="true"         android:layout_margintop="25dp"         android:textappearance="?android:attr/textappearancemedium"         android:onclick="onpingclick"         android:text="@string/ping" />  </relativelayout> 

you can see there 2 editviews user enter in seconds (edit_seconds) , message (edit_reminder). there button called ping, when press sends data serviceintent.

below code mainactivity.java:

/*  * copyright (c) 2012 android open source project  *  * licensed under apache license, version 2.0 (the "license"); may not use file except  * in compliance license. may obtain copy of license @  *  * http://www.apache.org/licenses/license-2.0  *  * unless required applicable law or agreed in writing, software distributed under license  * distributed on "as is" basis, without warranties or conditions of kind, either express  * or implied. see license specific language governing permissions , limitations under  * license.  */  package com.example.android.pingme;  import android.app.activity; import android.content.intent; import android.os.bundle; import android.view.view; import android.widget.edittext; import android.widget.toast;  public class mainactivity extends activity {      private intent mserviceintent;      @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          // creates explicit intent start service constructs ,         // issues notification.         mserviceintent = new intent(getapplicationcontext(), pingservice.class);     }      /*      * gets values user entered , adds them intent      * used launch intentservice runs timer , issues      * notification.      */     public void onpingclick(view v) {         int seconds;          // gets reminder text user entered.         edittext msgtext = (edittext) findviewbyid(r.id.edit_reminder);         string message = msgtext.gettext().tostring();          mserviceintent.putextra(commonconstants.extra_message, message);         mserviceintent.setaction(commonconstants.action_ping);         toast.maketext(this, r.string.timer_start, toast.length_short).show();          // number of seconds timer should run.         edittext edittext = (edittext)findviewbyid(r.id.edit_seconds);         string input = edittext.gettext().tostring();          if(input == null || input.trim().equals("")){             // if user didn't enter value, sets default.             seconds = r.string.seconds_default;         } else {             seconds = integer.parseint(input);         }         int milliseconds = (seconds * 1000);         mserviceintent.putextra(commonconstants.extra_timer, milliseconds);         // launches intentservice "pingservice" set timer.         startservice(mserviceintent); 

you can see above in onpingclick(view v) method both edittexts referenced variables "msgtext" , "edittext". ping button never referenced nor listener attached button starts services when button pressed. however, app works on both emulator , phone without button being referenced.

how android know clicking button means method onpingclick(view v) must actioned?

because in xml layout button specified : android:onclick="onpingclick"
sets onclicklistener outside java code.

note method mus satisfy signature:

public void somename(view v) 

it way set click listener view.