Develop Reference

Problems with the event treatment of a Button

Something very weird is happening in my program. I try to use the button with the first program below (using an emulator) and the program did not even open. So I changed to the second version, using the android:OnClick, and it did not work either (the program opened, but in the click it crashed). Then I tried the third program, using android:onCLick and the instanciation of the EditText in the treatment function, and the program worked.
Can someone explain to me why the first two programs did not worked?
Edit: I noticed now that LogCat is pointing to the following error: error opening trace file: No such file oor directory (2), what is that? Can it have any relation to this error?
And if I comment the definition of the onClickListener to b1 the program do not crash anymore.
First code:
package app.projetnf33;
import android.app.Activity;
import android.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.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
public class MainActivity extends Activity implements OnClickListener{
String[] names;
EditText status;
EditText par1;
EditText par2;
EditText par3;
Button b1;
Button b2;
Button b3;
Button b4;
Spinner spin;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status = (EditText) findViewById(R.id.text);
b1 = (Button) findViewById(R.id.b1);
b1.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v) {
status.setText("Connect");
}
});
if (savedInstanceState == null) {
getFragmentManager().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;
}
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
Second code
package app.projetnf33;
import android.app.Activity;
import android.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.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
public class MainActivity extends Activity implements OnClickListener{
String[] names;
EditText status;
EditText par1;
EditText par2;
EditText par3;
Button b1;
Button b2;
Button b3;
Button b4;
Spinner spin;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status = (EditText) findViewById(R.id.text);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
public void treatment_connect(View v){
status.setText("Connect");
}
public void treatment_persons(View v){
status.setText("Persons");
}
public void treatment_lecture(View v){
status.setText("Lecture");
}
public void treatment_execute(View v){
status.setText("Execute");
}
#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;
}
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
Third code (which worked):
package app.projetnf33;
import android.app.Activity;
import android.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.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
public class MainActivity extends Activity implements OnClickListener{
String[] names;
EditText status;
EditText par1;
EditText par2;
EditText par3;
Button b1;
Button b2;
Button b3;
Button b4;
Spinner spin;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
public void treatment_connect(View v){
status = (EditText) findViewById(R.id.text);
status.setText("Connect");
}
public void treatment_persons(View v){
status.setText("Persons");
}
public void treatment_lecture(View v){
status.setText("Lecture");
}
public void treatment_execute(View v){
status.setText("Execute");
}
#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;
}
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
Fragment_layout:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/tex_status" />
<EditText
android:id="#+id/text"
android:inputType="text"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<Spinner
android:id="#+id/spinner"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/par1" />
<EditText
android:id="#+id/par1"
android:inputType="text"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/par2" />
<EditText
android:id="#+id/par2"
android:inputType="text"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/par3" />
<EditText
android:id="#+id/par3"
android:inputType="text"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="#+id/b1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableLeft="#drawable/ic_action_usb"
android:gravity="center_vertical"
android:text="#string/connect"
android:onClick="treatment_connect" />
<Button
android:id="#+id/b2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:drawableLeft="#drawable/ic_action_computer"
android:gravity="center_vertical"
android:text="#string/read"
android:onClick="treatment_lecture" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="#+id/b3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableLeft="#drawable/ic_action_accept"
android:gravity="center_vertical"
android:text="#string/execution"
android:onClick="treatment_execution" />
<Button
android:id="#+id/b4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:drawableLeft="#drawable/ic_action_warning"
android:gravity="center_vertical"
android:text="#string/disconnect"
android:onClick="treatment_disconnect" />
</LinearLayout>
</LinearLayout>

In the first and seconds layout you tried to call
status = (EditText) findViewById(R.id.text);
b1 = (Button) findViewById(R.id.b1);
before
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
So you tried to reference a Button and EditText contained in the PlaceholderFragment layout before you created the fragment.

The views are in the fragment layout. It only becomes a part of the activity view hierarchy after the fragment transaction has been run. Your pending fragment transaction is executed in activity super.onStart() which comes only after onCreate(). In essence, you're calling findViewById() too early in the first two versions. The third version works because the findViewById() is in the click handler and gets invoked when the fragment is attached to the activity.
Usually you'd call findViewById() to set up listeners and so on at the earliest possibility in fragment onCreateView(), just after the fragment layout is inflated.

App crashes when adding onClickListener Android [duplicate]

This question already has answers here:
setOnClickListener crashs my android app
(3 answers)
Closed 8 years ago.
I don't know why but I can't seem to figure out what is wrong with my code. As soon as I add an onclickListener the app crashes. I really need help. Also I looked at other threads but I can't seem to find out what I'm doing wrong. Thanks
The code is below:
package com.example.medrec;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.AlertDialog;
import android.os.Bundle;
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.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.Toast;
import android.os.Build;
public class MainActivity extends ActionBarActivity implements OnClickListener{
Button login;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
login = (Button)findViewById(R.id.w_login);
//Crashes when I add this line.
login.setOnClickListener(this);
}
#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;
}
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
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="com.example.medrec.MainActivity"
tools:ignore="MergeRootFrame" />
My 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: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.medrec.MainActivity$PlaceholderFragment" >
<EditText
android:id="#+id/w_number_edit_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="21dp"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="118dp"
android:text="#string/w_number" />
<Button
android:id="#+id/w_login"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/w_number_edit_text"
android:layout_centerHorizontal="true"
android:layout_marginTop="15dp"
android:text="#string/w_login_text" />

try below code:-
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);
login = (Button)rootView.findViewById(R.id.w_login);
//Crashes when I add this line.
login.setOnClickListener(this);
return rootView;
}
}

I'm assumging it's crashing because your login is null, the reason it's null because w_login doesn't exist in your activity layout. Try this (rootView from your fragment),
login = (Button) rootView.findViewById(R.id.w_login);
login.setOnClickListener(this);

Your app crashed it's because your button w_login belong to your fragment_main.xml and you have to set activity_main.xml layout to your Activity.
At code
login = (Button) rootView.findViewById(R.id.w_login);
login.setOnClickListener(this);
You should reference this Button in your Fragment onCreateView(......)

assign on click listener in onCreateView
login = (Button) rootView.findViewById(R.id.w_login);
//Crashes when I add this line.
login.setOnClickListener(this);

Your app crashes showing NullPointerException while searching the Button in your activity_main.xml but it doesn't find there. Rather you should add the button code in your PlaceholderFragment fragment.
Delete the following line from your MainActivity
login = (Button)findViewById(R.id.w_login);
//Crashes when I add this line.
login.setOnClickListener(this);
Add the following to your PlaceholderFragment
public static class PlaceholderFragment extends Fragment implements OnClickListener{
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button login = (Button)rootView.findViewById(R.id.w_login);
login.setOnClickListener(this);
return rootView;
}
}

Android app stop when is being to run

I'm new to android and java. this is my first app. an example of a book. I did all steps according the book. the app is going to increase the number by click on + button
this is my Java file :
package com.example.myprayercounter;
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.widget.Button;
import android.widget.TextView;
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 {
int counter;
TextView tView;
Button btn;
public PlaceholderFragment() {}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
counter = 0;
tView = (TextView)getActivity().findViewById(R.id.txt_textTwo);
btn = (Button)getActivity().findViewById(R.id.btn_buttonOne);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
counter++;
tView.setText(" " + counter);
}
});
return rootView;
}
}
}
xml file :
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#fbfbdd"
android:gravity="center_horizontal"
android:orientation="vertical"
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.myprayercounter.MainActivity$PlaceholderFragment" >
<TextView
android:id="#+id/txt_textOne"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="تعداد ذکرهای من"
android:textColor="#763f05"
android:textSize="20dp" />
<TextView
android:id="#+id/txt_textTwo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textColor="#763f05"
android:textSize="40dp" />
<Button
android:id="#+id/btn_buttonOne"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#763f05"
android:text="+"
android:textColor="#fbfbdd"
android:textSize="40dp" />
</LinearLayout>
I got this error at first run of the app :
What is my mistakes? and how i can fix them?
Thanks in advance

change:
tView = (TextView)getActivity().findViewById(R.id.txt_textTwo);
btn = (Button)getActivity().findViewById(R.id.btn_buttonOne);
to ( getActivity() --> rootView)
tView = (TextView)rootView.findViewById(R.id.txt_textTwo);
btn = (Button)rootView.findViewById(R.id.btn_buttonOne);
in PlaceholderFragment, your View is rootView and you need find your view from that

Android TextView is failing with null pointer exception

Android TextView is failing with null pointer exception
and its failing at "disp.setText("0");"
inside the method "protected void onCreate(Bundle savedInstanceState) {"
I tried most of the suggestions provided in net. Still could not resolve it.
Please need help....
My Layout: "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:onClick="num_Clicked"
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.ullas.Test1.MainActivity$PlaceholderFragment" >
<TextView
android:id="#+id/textView1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="17dp"
android:gravity="right"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
and My Activity is : "MainActivity.java"
import android.support.v7.app.ActionBarActivity;
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.widget.*;
public class MainActivity extends ActionBarActivity {
TextView disp;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
disp = (TextView)findViewById(R.id.textView1);
disp.setText("0");
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
}
}

you tell your layout is "fragment_main.xml" and textview is in this xml.
in your code, you are setting a different layout xml:
setContentView(R.layout.activity_main);
disp = (TextView)findViewById(R.id.textView1);
you must set the layout you want to use, in order to be able to reach your textview:
setContentView(R.layout.fragment_main);
disp = (TextView)findViewById(R.id.textView1);

The view textView1 is not found in the layout file loaded. View hierarchy should be created before getting view from the layout.

Complete "MainActivity.java" is below
package com.example.test;
import android.app.Activity;
import android.app.ActionBar;
import android.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.widget.TextView;
import android.os.Build;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView disp;
disp = (TextView) findViewById(R.id.textView1);
disp.setText("0");
if (savedInstanceState == null) {
getFragmentManager().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;
}
}
}
and Below is the Complete "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: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.test.MainActivity$PlaceholderFragment" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginTop="30dp"
android:gravity="right"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
Below is the "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="com.example.test.MainActivity"
tools:ignore="MergeRootFrame" />
and ONE MORE THING , WHEN I CREATE A NEW PROJECT BY DEFAULT IT WILL GIVE ME THIS "Fragment_main.xml"

Android app error "Unfortunately the app is stopped"

I am using Android studio for android development.I am creating onclick button activity.I am getting no errors but when I click the button on the app it shows "Unfortunately the app has stopped."
Below is my code for fragment_main.xml and MainActivity.java.
Please guide.
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">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/texthaiku"
android:id="#+id/button"
android:layout_alignParentTop="true"
android:layout_toRightOf="#+id/editText"
android:onClick="OnLoveButtonClicked"/>
<TextView
android:text="#string/haiku"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/textView"
android:layout_below="#+id/button"
android:visibility="invisible"
android:layout_alignParentLeft="true"
android:layout_marginTop="33dp" />
</RelativeLayout>
MainActivity.java
package com.AndroidLove;
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.widget.TextView;
import android.widget.Button;
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();
}
}
public void onLoveButtonClicked(View view) {
TextView textView =(TextView) findViewById(R.id.textView);
textView.setVisibility(View.VISIBLE);
}
#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.
switch (item.getItemId()) {
case 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;
}
}
}

Try this..
It'll give NPE because textView is inside fragment_main.xml then your initilize that textview inside click function that's wrong . use that textView in global
TextView textView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
textView =(TextView) rootView.findViewById(R.id.textView);
return rootView;
}
and
public void onLoveButtonClicked(View view) {
textView.setVisibility(View.VISIBLE);
}

where did you create container, in xml which you have shown i don't see any container layout.
without R.id.container

you have not initialized your TextView on onCreateView()
so add this line on onCreateView()
textView =(TextView) rootView.findViewById(R.id.textView);
EDIT
initialize your button also.
btn = (Button) rootView.findViewById(R.id.button);