Develop Reference

Android Studio: SearchView: error in searchView.setSearchableInfo(searchManager.getSearchableInfo(cn));

I'm a newbie working on an android app, following is the first screen of the app. I want my application to perform search using that search dialog box.
For this, I followed http://developer.android.com/guide/topics/search/search-dialog.html
But I was getting following error:
Logcat:
FATAL EXCEPTION: main
Process: com.example.shalini.circlelayout, PID: 19330
java.lang.NullPointerException
at com.example.shalini.circlelayout.MainActivity.onCreateOptionsMenu(MainActivity.java:69)
where line:69 in MainActivity.java is:
ComponentName cn = new ComponentName(this, SearchResultsActivity.class);
searchView.setSearchableInfo(searchManager.getSearchableInfo(cn));
I referred to this
Cannot get searchview in actionbar to work
and made changes but the same problem still persists. My question is why is it showing error in searchView.setSearchableInfo(searchManager.getSearchableInfo(cn)); line. I couldn't figure that out, I still think that error is arising due to some other part of the code, maybe searchresultsactivity.xml or SearchResultsActivity.java. Any help is much appreciated. Thank you.
Code below:
MainActivity.java
package com.example.shalini.circlelayout;
import android.app.SearchManager;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.SearchView;
import android.support.v7.widget.Toolbar;
import android.view.MenuInflater;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.ImageButton;
public class MainActivity extends AppCompatActivity {
EditText e1;
ImageButton imageButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
e1 = (EditText) findViewById(R.id.search);
addListenerOnButton();
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
private void addListenerOnButton() {
imageButton = (ImageButton) findViewById(R.id.imageButton);
imageButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), SymptomsList.class);
startActivity(i);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_main, menu);
// Associate searchable configuration with the SearchView
SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE);
SearchView searchView = (SearchView) menu.findItem(R.id.search).getActionView();
ComponentName cn = new ComponentName(this, SearchResultsActivity.class);
searchView.setSearchableInfo(searchManager.getSearchableInfo(cn));
//call to getSearchableInfo()
//SearchableInfo object
//SearchView starts an activity with the ACTION_SEARCH intent when a user submits a query
return true;
}
#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);
}
}
SearchResultsActivity.java
package com.example.shalini.circlelayout;
import android.app.ListActivity;
import android.app.SearchManager;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
public class SearchResultsActivity extends ListActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
handleIntent(getIntent());
}
#Override
public void onNewIntent(Intent intent) {
super.onNewIntent(intent);
handleIntent(intent);
}
private void handleIntent(Intent intent) {
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
doMySearch(query);
//use the query to search your data somehow
}
}
private void doMySearch(String query) {
Log.d("Event", query);
}
}
content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="wrap_content" android:padding="#dimen/activity_horizontal_margin"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
tools:showIn="#layout/activity_main" tools:context=".MainActivity"
android:background="#drawable/blue_bluecrop1">
<EditText
android:layout_width="160dp"
android:layout_height="60dp"
android:id="#+id/search"
android:inputType="text"
android:hint="#string/sym"
android:drawableStart="#drawable/search_s2"
android:drawableLeft="#drawable/search_s2"
android:padding="20dp"
android:gravity="center_vertical|center_horizontal"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp"
android:layout_marginTop="5dp"
android:ellipsize="end"
android:background="#drawable/roundededittext"/>
<ImageButton
android:layout_width="40dp"
android:layout_height="45dp"
android:contentDescription="#string/symbutton"
android:id="#+id/imageButton"
android:background="#00000000"
android:layout_marginLeft="160dp"
android:layout_marginStart="160dp"
android:layout_marginTop="270dp"
android:clickable="true"
/>
searchresultsactivity.xml
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
#xml/searchable
<?xml version="1.0" encoding="utf-8"?>
<searchable xmlns:android="http://schemas.android.com/apk/res/android"
android:label="#string/app_name"
android:hint="#string/search_searchable">
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.shalini.circlelayout" >
<application
android:allowBackup="true"
android:fullBackupContent="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="#string/app_name"
android:theme="#style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="http"
android:host="www.example.com"
android:pathPrefix="/doraemon" />
</intent-filter>
<meta-data
android:name="android.app.default_searchable"
android:value=".SearchResultsActivity" />
</activity>
<activity android:name=".SearchResultsActivity">
<intent-filter>
<action android:name="android.intent.action.SEARCH" />
</intent-filter>
<meta-data android:name="android.app.searchable"
android:resource="#xml/searchable" />
</activity>
</application>

Your searchView seems to be null. How did you make it?

Run android App Error (FATAL EXCEPTION: main Process: PID: 14099)

I have below code and have below Error when run App PLZ Help me
Main Activity
package com.comp.easybuy.easybuy;
import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.content.Context;
import android.content.Intent;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import static android.net.Uri.parse;
public class MainActivity extends Activity {
private ImageButton callusphone;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
ImagePagerAdapter adapter = new ImagePagerAdapter();
viewPager.setAdapter(adapter);
callusphone=(ImageButton)findViewById(R.id.callus);
callusphone.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent callIntent = new Intent(Intent.ACTION_CALL, parse("tel:+962796880853"));
startActivity(callIntent);
}
});
}
public void flick(View view){
Intent bowsprit =new Intent(Intent.ACTION_VIEW, parse("http://www.facebook.com/ebuy2015/"));
startActivity(bowsprit);
}
public void incline(View view){
Intent browbeaten =new Intent(Intent.ACTION_VIEW, parse("http://www.instagram.com/easy_buy_1/"));
startActivity(browbeaten);
}
private class ImagePagerAdapter extends PagerAdapter {
private int[] mImages = new int[] {
R.drawable.offer4,
R.drawable.offer5,
R.drawable.offer6,
};
#Override
public int getCount() {
return mImages.length;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Context context = MainActivity.this;
ImageView imageView = new ImageView(context);
int padding =context.getResources().
getDimensionPixelSize(R.dimen.abc_switch_padding);
imageView.setPadding(padding, padding, padding, padding);
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
imageView.setImageResource(mImages[position]);
container.addView(imageView, 0);
return imageView;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((ImageView) object);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#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);
}
}
Splash screen
package com.comp.easybuy.easybuy;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class Splash extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.splash);
Thread timerThread = new Thread(){
public void run(){
try{
sleep(3000);
}
catch(InterruptedException e){
e.printStackTrace();
}
finally{
Intent intent = new Intent(Splash.this,MainActivity.class);
startActivity(intent);
}
}
};
timerThread.start();
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
finish();
}
}
Manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.comp.easybuy.easybuy">
<uses-permission android:name="ANDROID.PERMISSION.CALL_PHONE"/>
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".Splash"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".MainActivity"
android:label="#string/app_name"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
main Activity
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin">
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/imageButton"
android:onClick="flick"
android:src="#drawable/fbook"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="false"
android:scaleType="center"
android:contentDescription="facebook Image Button"
android:layout_alignParentStart="false"
android:theme="#style/Widget.AppCompat.RatingBar"
android:visibility="visible" />
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/insta"
android:onClick="incline"
android:src="#drawable/inst"
android:layout_alignParentBottom="true"
android:layout_alignTop="#+id/imageButton"
android:layout_alignParentEnd="false"
android:layout_alignParentStart="false"
android:scaleType="center"
android:theme="#style/Widget.AppCompat.RatingBar"
android:visibility="visible" />
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/callus"
android:onClick="callusphone"
android:src="#drawable/callus"
android:layout_alignParentBottom="false"
android:layout_centerHorizontal="true"
android:layout_marginLeft="145dp"
android:layout_marginRight="145dp"
android:layout_below="#+id/view_pager"
android:layout_alignParentEnd="false"
android:layout_alignParentStart="false"
android:scaleType="center"
android:theme="#style/Widget.AppCompat.RatingBar"
android:visibility="visible" />
<android.support.v4.view.ViewPager
android:id="#+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignWithParentIfMissing="false"
android:layout_gravity="right|left"
android:visibility="visible"
android:background="#ffffff"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_above="#+id/imageButton" />
</RelativeLayout>
and have Error
08-19 09:30:36.123 14099-14099/com.comp.easybuy.easybuy E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.comp.easybuy.easybuy, PID: 14099
java.lang.IllegalArgumentException: Expected receiver of type com.comp.easybuy.easybuy.MainActivity, but got android.view.ContextThemeWrapper
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4448)
at android.view.View.performClick(View.java:5199)
at android.view.View$PerformClick.run(View.java:21155)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5415)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:725)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:615)

First declare Your Image Buttons as below
imageFb=(ImageButton)findViewById(R.id.imageButton);
imageInsta=(ImageButton)findViewById(R.id.insta);
and use OnClickListener
imageFb.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
flick(v);
}
});
imageInsta.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
incline(v);
}
});
check now it should work!! You have defined your onClick in xml but havent used it and passed the view to method so it was crashing your code!
final MainActivity should look like this!
package com.comp.easybuy.easybuy;
import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.content.Context;
import android.content.Intent;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import static android.net.Uri.parse;
public class MainActivity extends Activity {
private ImageButton callusphone;
private ImageButton imageFb;
private ImageButton imageInsta;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
ImagePagerAdapter adapter = new ImagePagerAdapter();
viewPager.setAdapter(adapter);
callusphone=(ImageButton)findViewById(R.id.callus);
imageFb=(ImageButton)findViewById(R.id.imageButton);
imageInsta=(ImageButton)findViewById(R.id.insta);
callusphone.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent callIntent = new Intent(Intent.ACTION_CALL, parse("tel:+962796880853"));
startActivity(callIntent);
}
});
imageFb.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
flick(v);
}
});
imageInsta.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
incline(v);
}
});
}
public void flick(View view){
Intent bowsprit =new Intent(Intent.ACTION_VIEW, parse("http://www.facebook.com/ebuy2015/"));
startActivity(bowsprit);
}
public void incline(View view){
Intent browbeaten =new Intent(Intent.ACTION_VIEW, parse("http://www.instagram.com/easy_buy_1/"));
startActivity(browbeaten);
}
private class ImagePagerAdapter extends PagerAdapter {
private int[] mImages = new int[] {
R.drawable.offer4,
R.drawable.offer5,
R.drawable.offer6,
};
#Override
public int getCount() {
return mImages.length;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Context context = MainActivity.this;
ImageView imageView = new ImageView(context);
int padding =context.getResources().
getDimensionPixelSize(R.dimen.abc_switch_padding);
imageView.setPadding(padding, padding, padding, padding);
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
imageView.setImageResource(mImages[position]);
container.addView(imageView, 0);
return imageView;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((ImageView) object);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#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);
}
}

Failed to receive Intent from parent activity?

I'm following the tutorial from the following link: https://developer.android.com/training/basics/firstapp/starting-activity.html
The problem I'm facing is, I able to trigger the sendMessage method however it just failed to show the expected result?
Please take a look at the following code:
activity_main.xml (Parent layout):
<EditText android:id="#+id/edit_message"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:hint="#string/edit_message" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/button_send"
android:onClick="sendMessage"/>
</LinearLayout>
MainActivity.java:
package com.example.myfirstapp;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends ActionBarActivity {
public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/** Called when the user clicks the Send button */
public void sendMessage(View view) {
// Do something in response to button
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
}
}
activity_display_message.xml (Children layout):
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.myfirstapp.DisplayMessageActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
</RelativeLayout>
DisplayMessageActivity.java:
package com.example.myfirstapp;
import android.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class DisplayMessageActivity extends ActionBarActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get the message from the intent
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
// Create the text view
TextView textView = new TextView(this);
textView.setTextSize(40);
textView.setText(message);
// Set the text view as the activity layout
setContentView(textView);
}
#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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() { }
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_display_message,
container, false);
return rootView;
}
}
}
MyFirstApp Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myfirstapp"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="16" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".DisplayMessageActivity"
android:label="#string/title_activity_display_message"
android:parentActivityName=".MainActivity" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.myfirstapp.MainActivity" />
</activity>
</application>
</manifest>
P/S: I've set a breakpoint at DisplayMessageActivity.java onCreate() method but it wasn't being triggered.

You are missing a startActivity statement. Your MainActivity.sendMessage it should be like the follwing:
/** Called when the user clicks the Send button */
public void sendMessage(View view) {
// Do something in response to button
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent); /// <---- THIS LINE
}
Hope it helps

Add below line
startActivity(intent);
under
intent.putExtra(EXTRA_MESSAGE, message);
And Call sendMessage() on button click

Add
startActivity(intent)
after this line
intent.putExtra(EXTRA_MESSAGE, message);
This why there's no response upon clicking the button.

1) You are not attaching Listener to your button. Do it like :
Button myButton = (Button) findViewById(R.id.my_button);
myButton.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View v,
int position, long id) {
sendMessage(); //this is the action to be taken.
}
});
2) You are creating the Intent object, but not firing it. Use startActivity(intent) as the last line of sendMessage() method to fire the intent and get the desired results.

Shifting between activities (Android)

Shifting between activities isn't working.
What the app does is it opens the android.xml file then after 5 secs open the main file
Here's the code:
android manifest file:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.android.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.android.android"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.ANDROID" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
android.java file:
package com.example.android;
import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
public class android extends Activity{
MediaPlayer sound1;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.android);
sound1 = MediaPlayer.create(android.this , R.raw.android);
sound1.start();
Thread timer = new Thread()
{public void run()
{
try{
sleep(5000);
}
catch(InterruptedException ac){
ac.printStackTrace();
}
finally{
Intent openactivity = new Intent ("android.intent.action.MAIN");
startActivity(openactivity);
}
}
};
timer.start();
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
sound1.release();
finish();
}
}
Mainactivity.java:
package com.example.android;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
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.os.Build;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends 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;
}
}
}
android.xml file:(the first file that launches up)
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background = "#drawable/android"
>
</LinearLayout>

Try this way
Intent openactivity = new Intent(android.this,MainActivity.class);
startActivity(openactivity);
And for more information go to starting-new-activity

First, always Capitalise 1st letter of class names (code convention),
and then write your intents like below:
Intent intent = new Intent(android.this, MainActivity.class);
startActivity(intent );
You can check Starting Another Activity in Android Developers website.

Android Emulator crash "Unfortunately _app name_ has stopped"

I have seen a few answers to questions on this topic but I see that those answers change depending on the coding of the app.
I am new to android apps and the tutorial Im following uses one button to increment and another one to reduce a counter. I get this "Unfortunately AddSubb has stoped" error on my emulator.
MainActivity.java
package com.example.addingsubstracting;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
int counter;
Button add, sub;
TextView display;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
counter = 0;
add = (Button) findViewById(R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.tvDisplay);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter++;
display.setText("Your total is " + counter);
}
});
sub.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter--;
display.setText("Your total is " + counter);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends 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;
}
}
}
fragment_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Yout total is 0"
android:textSize="20dp"
android:id="#+id/tvDisplay" />
<Button
android:layout_width="250dp"
android:layout_height="wrap_content"
android:text="Add one"
android:layout_gravity="center"
android:textSize="30dp"
android:id="#+id/bAdd" />
<Button
android:layout_width="250dp"
android:layout_height="wrap_content"
android:text="Substract one"
android:layout_gravity="center"
android:textSize="30dp"
android:id="#+id/bSub" />
</LinearLayout>
Manifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.addingsubstracting"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.addingsubstracting.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

This is because findViewById() searches in the activity_main layout, while the button is located in the fragment's layout fragment_main.
Move that piece of code in the onCreateView() method of the fragment:
eg:
//...
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button add = (Button)rootView.findViewById(R.id.R.id.bAdd);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter++;
display.setText("Your total is " + counter);
}
});
Notice that now you access it through rootView view:
eg:
Button buttonClick = (Button)rootView.findViewById(R.id.button);
otherwise you would get again NullPointerException.