Develop Reference

Getting "Unfortunately, app has stopped" while executing

I am learning Android dev in Android Studio.
I created an app which displays some text on fling and some other on click of a button.
But its showing "Unfortunately app has stopped"
Also, I have only one activity. So, its not possible that I forgot to show it in AndroidManifest.xml
here is my java code :
package com.example.mahe.pro2;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Button;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.support.v4.view.GestureDetectorCompat;
public class MainActivity extends AppCompatActivity implements GestureDetector.OnGestureListener {
private TextView tv = (TextView) findViewById(R.id.t);
private GestureDetectorCompat gd;
private Button bt = (Button) findViewById(R.id.b);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.gd = new GestureDetectorCompat(this,this);
bt.setOnClickListener(
new Button.OnClickListener() {
public void onClick(View v) {
tv.setText("That was a Click!");
}
}
);
}
#Override
public void onLongPress(MotionEvent motionEvent) {
}
#Override
public boolean onSingleTapUp(MotionEvent motionEvent) {
return false;
}
#Override
public boolean onScroll(MotionEvent motionEvent, MotionEvent motionEvent1, float v, float v1) {
return false;
}
#Override
public void onShowPress(MotionEvent motionEvent) {
}
#Override
public boolean onDown(MotionEvent motionEvent) {
return false;
}
#Override
public boolean onFling(MotionEvent motionEvent, MotionEvent motionEvent1, float v, float v1) {
tv.setText("That was a Swipe, Baby");
return true;
}
#Override
public boolean onTouchEvent(MotionEvent event) {
this.gd.onTouchEvent(event);
return super.onTouchEvent(event);
}
#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);
}
}
Here's my xml code :
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin" tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="YO!"
android:id="#+id/t"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="62dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Click"
android:id="#+id/b"
android:layout_below="#+id/t"
android:layout_centerHorizontal="true"
android:layout_marginTop="164dp" />

Just move
TextView tv = (TextView) findViewById(R.id.t);
Button bt = (Button) findViewById(R.id.b);
under onCreate(...) after setContentView(R.layout.activity_main);

as #M D said
you must first create your view and setview to can get R.id.b
but if you want to declare them as a global variable , use
private TextView tv;
private Button bt
above the onCreate Method , then in onCreate method and under
setContentView(R.layout.activity_main);
use
tv = (TextView) findViewById(R.id.t);
bt = (Button) findViewById(R.id.b);

xml layout loads but my activity doesn't respond to button clicks

I'm new at this but I already made a small app that worked the same way.
I can't see what I'm doing wrong because the code looks quiet the same as my previous app.
When I run it or debug my app it shows my layout on my emulator so it does load the page that has to be loaded but that's all it does, it doesn't listen to button clicks. I also gives me no errors.
Here's my XML code for fragment_main.xml
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment">
<TextView
android:text="Eventaris"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:textSize="100px"
android:textStyle="bold"
android:id="#+id/lblEventaris"
/>
<LinearLayout
android:layout_width="500px"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:orientation="vertical"
android:id="#+id/login">
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Gebruikersnaam"
android:id="#+id/txtGebruikersnaam"/>
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Wachtwoord"
android:inputType="textPassword"
android:layout_below="#id/txtGebruikersnaam"
android:id="#+id/txtWachtwoord"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Inloggen"
android:id="#+id/btnInloggen"
android:layout_below="#id/txtWachtwoord"/>
</LinearLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:layout_below="#id/login">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="nog geen account?"
android:gravity="center"
android:id="#+id/lblRegistratie"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Registeren"
android:id="#+id/btnRegistreren"
android:layout_below="#id/lblRegistratie"/>
</RelativeLayout>
</RelativeLayout>
Here's my fragmennt activity MainFragment.Java
package com.example.arno.eventaris;
import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import java.sql.SQLException;
/**
* Created by Arno on 28/04/2015.
*/
public class MainFragment extends Fragment {
private OnMainFragmentInteractionListener mListener;
private View view;
public MainFragment()
{
//required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
view=inflater.inflate(R.layout.fragment_main, container, false);
Button btnInloggen = (Button) view.findViewById(R.id.btnInloggen);
btnInloggen.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
inloggen();
} catch (SQLException e) {
e.printStackTrace();
}
}
});
Button btnRegistreren = (Button) view.findViewById(R.id.btnRegistreren);
btnRegistreren.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
navigeerRegistratie();
}
});
return view;
}
#Override
public void onAttach(Activity activity)
{
super.onAttach(activity);
try{
mListener = (OnMainFragmentInteractionListener) activity;
}
catch (ClassCastException e)
{
throw new ClassCastException(activity.toString() + "must implement OnFragmentInteractionListener");
}
}
public void inloggen() throws SQLException {
EditText gebr=(EditText) view.findViewById(R.id.txtGebruikersnaam);
EditText wachtw=(EditText) view.findViewById(R.id.txtWachtwoord);
String gebruiker = gebr.getText().toString();
String wachtwoord = wachtw.getText().toString();
mListener.login(gebruiker, wachtwoord);
}
public void navigeerRegistratie()
{
mListener.navigeerRegistratie();
}
#Override
public void onDetach()
{
super.onDetach();
mListener = null;
}
public interface OnMainFragmentInteractionListener {
//Todo: Update argument type and name
public void login(String gebruiker, String wachtwoord) throws SQLException;
public void navigeerRegistratie();
}
}
Here is my Main Activity MainActivity.java
package com.example.arno.eventaris;
import android.app.DialogFragment;
import android.database.Cursor;
import android.graphics.Color;
import android.net.Uri;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
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.ViewGroup;
import android.os.Build;
import android.widget.LinearLayout;
import android.widget.Toast;
import com.example.arno.eventaris.Database.DBAdapter;
import java.sql.SQLException;
public class MainActivity extends ActionBarActivity implements MainFragment.OnMainFragmentInteractionListener,RegistratieFragment.OnRegistratieFragmentInteractionListener{
private Cursor gebruikerCursor;
#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.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);
}
#Override
public void login(String gebruiker, String wachtwoord) throws SQLException {
DBAdapter db = new DBAdapter(this);
db.open();
gebruikerCursor = db.getGebruiker(gebruiker);
if(gebruikerCursor.moveToFirst()) {
gebruikerCursor.moveToFirst();
String wwControle = gebruikerCursor.getString(gebruikerCursor.getColumnIndex("wachtwoord"));
if (wachtwoord.equals(wwControle)) {
HomeFragment fragment = new HomeFragment();
Bundle bundle = new Bundle();
bundle.putString("gebruikersnaam", gebruiker);
fragment.setArguments(bundle);
getFragmentManager().beginTransaction().replace(R.id.container, fragment).commit();
} else {
DialogFragment errorlogin = new ErrorLogin();
errorlogin.show(getFragmentManager(), "Wachtwoord incorrect!");
}
}
else
{
DialogFragment errorlogin = new ErrorLogin();
errorlogin.show(getFragmentManager(), "Gebruikersnaam incorrect!");
}
db.close();
}
#Override
public void navigeerRegistratie() {
getFragmentManager().beginTransaction().replace(R.id.container, new RegistratieFragment()).commit();
}
#Override
public void registreren(String gebruiker, String voornaam, String naam, String email, String wachtwoord, String herhaalWachtwoord) {
if(wachtwoord.equals(herhaalWachtwoord)) {
DBAdapter db = new DBAdapter(this);
db.open();
long id = db.insertGebruiker(gebruiker, voornaam, naam, email, wachtwoord);
getFragmentManager().beginTransaction().replace(R.id.container, new MainFragment()).commit();
}
else
{
DialogFragment errorregistratie = new ErrorRegistratie();
errorregistratie.show(getFragmentManager(), "Wachtwoorden komen niet overeen!");
}
}
/**
* 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;
}
}
}
And as last here is my activity_main.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:id="#+id/container"
android:layout_width="match_parent" android:layout_height="match_parent"
tools:context=".MainActivity" tools:ignore="MergeRootFrame" />
Thanks in advance!

Fixed it by making a new project with the same code, had to be a problem way deeper than my code.

How to dynamically add user input into a listView within a fragment?

Im trying to add text into a listview within a fragment but i keep getting an error: cannot find symbol method setListAdapter(ArrayAdapter).
I'm using this tutorial as reference but it only shows how to do it within a activity : http://wptrafficanalyzer.in/blog/dynamically-add-items-to-listview-in-android/
Im trying to move this over to a fragment. Can anyone help please i would highly appreciate it? heres my code :
MainActivity:
import android.app.Activity;
import android.os.Bundle;
import android.view.ActionMode;
import android.view.Menu;
import android.view.MenuItem;
import com.example.fragments.DeleteDialogueFragment;
import com.example.PeopleFragment;
public class MainActivity extends Activity implements PeopleFragment.PeopleFragmentListener, DeleteDialogueFragment.DeleteDialogueListener {
private final String TAG = "MAINACTIVITY";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PeopleFragment())
.commit();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
//INTERFACE METHODS
public void deleteCharacter(){
PeopleFragment peopleFragment = (PeopleFragment) getFragmentManager().findFragmentById(R.id.container);
peopleFragment.deleteCharacter();
}
}
PeopleFragment :
import android.app.Activity;
import android.app.DialogFragment;
import android.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.ActionMode;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import com.example.actionbardemo.R;
import java.util.ArrayList;
import java.util.Arrays;
public class PeopleFragment extends Fragment{
private final String TAG = "PEOPLEFRAGMENT";
private PeopleFragmentListener mListener;
private ArrayAdapter<String> mPeopleAdapter;
private ActionMode mActionMode;
private int mPersonSelected = -1;
/** Items entered by the user is stored in this ArrayList variable */
private ArrayList<String> pList = new ArrayList<String>();
public interface PeopleFragmentListener {
}
public static PeopleFragment newInstance() {
PeopleFragment fragment = new PeopleFragment();
return fragment;
}
public PeopleFragment() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ArrayList<String> people = new ArrayList<String>(Arrays.asList(getResources().getStringArray(R.array.people)));
mPeopleAdapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,people);
// Reference to the button of the layout main.xml
Button btn = (Button) getView().findViewById(R.id.btnAdd);
// Defining a click event listener for the button "Add"
View.OnClickListener listener = new View.OnClickListener() {
#Override
public void onClick(View v) {
EditText edit = (EditText) getView().findViewById(R.id.txtItem);
pList.add(edit.getText().toString());
edit.setText("");
mPeopleAdapter.notifyDataSetChanged();
}
};
// Setting the event listener for the add button
btn.setOnClickListener(listener);
// Setting the adapter to the ListView
setListAdapter(mPeopleAdapter);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
ListView peopleList = (ListView) rootView.findViewById(R.id.peopleList);
peopleList.setAdapter(mPeopleAdapter);
peopleList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
#Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
if(mActionMode != null){
return false;
}
mPersonSelected = position;
mActionMode = getActivity().startActionMode(mActionModeCallback);
return true;
}
});
return rootView;
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (PeopleFragmentListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement PeopleFragmentListener");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
//INTERFACE METHODS
public void deleteCharacter(){
mPeopleAdapter.remove(mPeopleAdapter.getItem(mPersonSelected));
mPeopleAdapter.notifyDataSetChanged();
}
public String getToDelete(){
return mPeopleAdapter.getItem(mPersonSelected);
}
//CONTEXTUAL ACTION BAR CALLBACK
private ActionMode.Callback mActionModeCallback = new ActionMode.Callback() {
// Called when the action mode is created; startActionMode() was called
#Override
public boolean onCreateActionMode(ActionMode mode, Menu menu) {
// Inflate a menu resource providing context menu items
MenuInflater inflater = mode.getMenuInflater();
inflater.inflate(R.menu.peoplemenu, menu);
return true;
}
// Called each time the action mode is shown. Always called after onCreateActionMode, but
// may be called multiple times if the mode is invalidated.
#Override
public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
return false; // Return false if nothing is done
}
// Called when the user selects a contextual menu item
#Override
public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
switch (item.getItemId()) {
case R.id.peopleDelete:
Log.i(TAG,mPeopleAdapter.getItem(mPersonSelected));
DialogFragment dialog = new DeleteDialogueFragment();
Bundle args = new Bundle();
args.putString("name",mPeopleAdapter.getItem(mPersonSelected));
dialog.setArguments(args);
dialog.show(getActivity().getFragmentManager(), "DeleteDiaglogueFragment");
mode.finish();
return true;
default:
return false;
}
}
// Called when the user exits the action mode
#Override
public void onDestroyActionMode(ActionMode mode) {
mActionMode = null;
}
};
}
activity_main.xml (layout):
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
tools:ignore="MergeRootFrame" />
fragment_main.xml (layout):
<?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">
<EditText
android:id="#+id/txtItem"
android:layout_width="240dp"
android:layout_height="wrap_content"
android:inputType="text"
android:hint="#string/hintTxtItem"/>
<Button
android:id="#+id/btnAdd"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/lblBtnAdd"
android:layout_toRightOf="#id/txtItem"/>
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/peopleList"
android:layout_gravity="center_horizontal" />
</LinearLayout>
strings.xml(values):
<string name="app_name">ActionBarDemo</string>
<string name="action_settings">Settings</string>
<string name="hintTxtItem">Enter an item here ...</string>
<string name="lblBtnAdd">Add Item</string>
<string name="txtEmpty">List is empty</string>
<string name="delete_confirm">Are you sure you want to delete</string>
<string name="delete">Delete</string>
<string name="cancel">Cancel</string>
<string-array name="people">
<item>person 1</item>
<item>person 2</item>
<item>person 3</item>
<item>person 4</item>
<item>person 5</item>
<item>person 6</item>
</string-array>

get null pointer error when trying to getText

I am new to Android, so please forgive my ignorance. I have tried searching the forums, but haven't been able to find anything to get this to work. I am trying to use .getText().toString() (see below), but get a java.lang.NullPointerException error. I changed my setContentView so that it would look at the fragment_main.xml, but still returns a null for my different components. The goal of this is very simple, just to change the text on the TextView, since I am just getting started. Any help would be appreciated.
package com.example.app;
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;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
Button changeTxt = (Button) findViewById(R.id.btnChangeText);
final TextView textView = (TextView) findViewById(R.id.txtMessage);
changeTxt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String text = textView.getText().toString();
if (text.contains("World")) {
textView.setText("Hello Android!");
}
else {
textView.setText(("Hello World!"));
}
}
});
}
public void onStart(){
super.onStart();
}
public void onResume(){
super.onResume();
}
public void onPause(){
super.onPause();
}
public void onStop(){
super.onStop();
}
public void onDestroy(){
super.onDestroy();
}
#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;
}
}
}
Here is the xml:
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Large Text"
android:id="#+id/txtMessage"
android:layout_gravity="center_horizontal" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change Text"
android:id="#+id/btnChangeText"
android:layout_gravity="center_horizontal" />
</LinearLayout>
Fllo, updated code:
XML fragment_main.xml
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Large Text"
android:id="#+id/txtMessage1"
android:layout_gravity="center_horizontal" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change Text"
android:id="#+id/btnChangeText1"
android:layout_gravity="center" />
</FrameLayout>
</LinearLayout>
main activity
package com.example.app;
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;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
public void onStart(){
super.onStart();
}
public void onResume(){
super.onResume();
}
public void onPause(){
super.onPause();
}
public void onStop(){
super.onStop();
}
public void onDestroy(){
super.onDestroy();
}
#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);
Button changeTxt = (Button) findViewById(R.id.btnChangeText);
final TextView textView = (TextView) findViewById(R.id.txtMessage);
changeTxt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view)
{
String text = textView.getText().toString();
if (text.contains("World"))
{
textView.setText("Hello Android!");
}
else
{
textView.setText(("Hello World!"));
}
}
});
return rootView;
}
}
}

The NullPointerException occurs because, it seems that you have the same layout for your Activity and your Fragment:
// Activity
setContentView(R.layout.fragment_main);
// Fragment
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
You need to check if your views (TextView & Button) are in the right layout and not into aonther (I guess activity_main).
Two solutions:
Copy/past your views inside fragment_main to activity_main and change setContentView(R.layout.activity_main).
Or let your views inside fragment_main and use the following code to find your view inside your Fragment, as follows:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button changeTxt = (Button) rootView.findViewById(R.id.btnChangeText);
final TextView textView = (TextView) rootView.findViewById(R.id.txtMessage);
changeTxt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String text = textView.getText().toString();
if (text.contains("World")) {
textView.setText("Hello Android!");
}
else {
textView.setText(("Hello World!"));
}
}
});
return rootView;
}
Hope this helps.
UPDATE:
1 . Remove your FrameLayout inside fragment_main. Create a new layout named activity_main and add the FrameLayout into it (with an id) as:
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/container" />
2 . Set this layout in onCreate method into your Activity like:
// onCreate method Activity
setContentView(R.layout.activity_main);
3 . Then, remove static in your Fragment declaration, this should be:
public class PlaceholderFragment ... { }
4 . Finally, when you try to find ids elements inside onCreateView method, you ALWAYS MUST to use the inflated view as:
rootView.findViewById(R.id.some_id_example);
Voila! This should work now.

ActionBarSherlock Side Menu Navigation Drawer

Im trying to use drawer toggle in an action bar with sherlock. This is my main activity:
import uk.co.senab.actionbarpulltorefresh.extras.actionbarsherlock.PullToRefreshAttacher;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.widget.DrawerLayout;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import com.actionbarsherlock.app.SherlockFragmentActivity;
import com.actionbarsherlock.view.MenuItem;
import com.mejorandroid.ejemplo3_clase3.fragments.MainFragment;
import com.mejorandroid.ejemplo3_clase3.fragments.TermsFragment;
public class MainActivity extends SherlockFragmentActivity
implements OnItemClickListener{
private ListView drawer_list;
private DrawerLayout drawer_layout;
private ActionBarDrawerToggle drawer_toggle;
private PullToRefreshAttacher pullToRefreshAttacher;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pullToRefreshAttacher = PullToRefreshAttacher.get(this);
drawer_list = (ListView) findViewById(R.id.left_drawer);
drawer_layout = (DrawerLayout) findViewById(R.id.drawer_layout);
ArrayAdapter<String> drawer_adapter = new ArrayAdapter<String>(this,
R.layout.drawer_list_item, getResources().getStringArray(
R.array.array_drawer_options));
drawer_list.setAdapter(drawer_adapter);
drawer_list.setOnItemClickListener(this);
selectItem(0);
drawer_toggle = new ActionBarDrawerToggle(this, drawer_layout, R.drawable.ic_drawer, R.string.drawer_open, R.string.drawer_close){
#Override
public void onDrawerClosed(View drawerView) {
supportInvalidateOptionsMenu();
}
#Override
public void onDrawerOpened(View drawerView) {
supportInvalidateOptionsMenu();
}
};
drawer_layout.setDrawerListener(drawer_toggle);
getSherlock().getActionBar().setDisplayHomeAsUpEnabled(true);
getSherlock().getActionBar().setHomeButtonEnabled(true);
}
#Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
drawer_toggle.syncState();
}
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
drawer_toggle.onConfigurationChanged(newConfig);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId() == android.R.id.home || drawer_toggle.onOptionsItemSelected(item)){
return true;
}
return super.onOptionsItemSelected(item);
}
#Override
public boolean onCreateOptionsMenu(com.actionbarsherlock.view.Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getSupportMenuInflater().inflate(R.menu.main, menu);
return true;
}
public PullToRefreshAttacher getAttacher() {
return pullToRefreshAttacher;
}
public void selectItem(int position){
Fragment f;
if(position==0){
f = new MainFragment();
}else{
f = new TermsFragment();
}
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction()
.replace(R.id.main_content, f)
.commit();
drawer_list.setItemChecked(position, true);
setTitle(drawer_list.getItemAtPosition(position).toString());
drawer_layout.closeDrawer(drawer_list);
}
#Override
public void onItemClick(AdapterView<?> arg0, View arg1, int position, long arg3) {
selectItem(position);
}
}
In the method onOptionsItemSelected:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId() == android.R.id.home || drawer_toggle.onOptionsItemSelected(item)){
return true;
}
return super.onOptionsItemSelected(item);
}
I get:
How can I fix this??
This is my main.xml:
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="#+id/main_content"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<ListView
android:id="#+id/left_drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:divider="#android:color/transparent"
android:dividerHeight="0dp"
android:background="#111"/>
</android.support.v4.widget.DrawerLayout>

I had the same problem and this works for me:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId() == android.R.id.home) {
if (drawer_layout.isDrawerOpen(drawer_list)) {
drawer_layout.closeDrawer(drawer_list);
} else {
drawer_layout.openDrawer(drawer_list);
}
}
return super.onOptionsItemSelected(item);
}
I don't know if this problem is already fixed in the newest release of the Sherlock library / support library, but the workaround does a good job.