Develop Reference

Navigation With CountDownTimer

I am trying to develop an application whereby there would be one activity with a start button. Upon pressing the start button, it would lead me to a new activity where the timer starts to run. I am only able to make it run when both buttons and textview is on the same page. However, I would like to have button on one activity and textview on another activity.
Java File:
import android.content.DialogInterface;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.view.View.OnClickListener;
public class MainActivity extends AppCompatActivity {
Button buttonStart;
TextView textCounter;
MyCountDownTimer myCountDownTimer;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonStart = (Button)findViewById(R.id.start);
textCounter = (TextView)findViewById(R.id.counter);
buttonStart.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
myCountDownTimer = new MyCountDownTimer(30000, 1000, textCounter);
myCountDownTimer.start();
}
});
}
public class MyCountDownTimer extends CountDownTimer {
private TextView textCounter;
public MyCountDownTimer(long millisInFuture, long countDownInterval, TextView textCounter) {
super(millisInFuture, countDownInterval);
this.textCounter = textCounter;
}
#Override
public void onTick(long millisUntilFinished){
this.textCounter.setText(millisUntilFinished / 1000l + " seconds remaining ");
}
#Override
public void onFinish() {
this.textCounter.setText("Finished");
}
}
#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);
}
}
Main_Activity:
<Button
android:id="#+id/start"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="#string/Button"
android:clickable="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
Main_Activity2:
<TextView
android:id="#+id/counter"
android:layout_width="300dp"
android:layout_height="300dp"
android:textStyle="bold"
android:textSize="50sp"
android:gravity="center"
android:layout_marginTop="50dp"
android:clickable="false"
android:enabled="false" />

Try this Code:
The code for Layout 1: activity_main.xml , Only with start button
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="#+id/start"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:clickable="true"
android:text="Start" />
</LinearLayout>
The code for Layout 2: count_down_activity.xml
<?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" >
<TextView
android:id="#+id/counter"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_marginLeft="50dp"
android:layout_marginTop="50dp"
android:gravity="center"
android:textSize="50sp"
android:textStyle="bold" />
</LinearLayout>
Java file: MainActivity.java
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
private Context mContext;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
Button startBrowser = (Button) findViewById(R.id.start);
startBrowser.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
startActivity(new Intent(mContext, CountDownActivity.class));
}
});
}
#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;
}
}
Java File 2: CountDownActivity.java
import android.app.Activity;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.view.Menu;
import android.widget.TextView;
public class CountDownActivity extends Activity {
TextView textCounter;
MyCountDownTimer myCountDownTimer;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.count_down_activity);
textCounter = (TextView)findViewById(R.id.counter);
myCountDownTimer = new MyCountDownTimer(30000, 1000, textCounter);
myCountDownTimer.start();
}
public class MyCountDownTimer extends CountDownTimer {
private TextView textCounter;
public MyCountDownTimer(long millisInFuture, long countDownInterval, TextView textCounter) {
super(millisInFuture, countDownInterval);
this.textCounter = textCounter;
}
#Override
public void onTick(long millisUntilFinished) {
this.textCounter.setText(millisUntilFinished / 1000l + " seconds remaining : ");
}
#Override
public void onFinish() {
this.textCounter.setText("Finished");
}
}
#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;
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.androidsample"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
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.androidsample.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="com.example.androidsample.CountDownActivity"
android:screenOrientation="portrait" >
</activity>
</application>
</manifest>

Changing text in textView

I am trying to change the text in one of the textview by calling it in a function that is assigned to a button.. However it is not quite working as I hoped. I was wondering if some one could point out why isn't it working?
Here is the "MainActivity.java" file
package com.nblsoft.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
#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.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);
}
String stri = new String("Hellow");
public void game(View view) {
TextView textv = (TextView) findViewById(R.id.textView2);
textv.setText(stri);
}
}
and the "activity_main.xml" file
<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="#string/Welcome"
android:id="#+id/textView"
android:gravity="center"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="#string/lower_text"
android:id="#+id/textView2"
android:layout_below="#+id/editText"
android:layout_centerHorizontal="true"
android:layout_marginTop="34dp" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/editText"
android:inputType="number"
android:text="#string/guess"
android:textSize="160dp"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:onClick="game"/>
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="ok"
android:id="#+id/button"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>

you want call game when click in EditText?! you put android:onClick="game" in EditText
if want call when click in Button you must add android:onClick="game" to your Button in activity_main.xml file like
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="ok"
android:id="#+id/button"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:onClick="game" />
or you can use this in MainActivity.java instead use android:onClick="game" in xml file
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button=(Button) findViewById(R.id.button);
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
game(arg0);
}
});
}
- remove android:onClick="game" from EditText

package com.nblsoft.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView textv = (TextView) findViewById(R.id.textView2);
String stri = new String("Hellow");
Button btn = (Button) findViewById(R.id.button);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
textv.setText(stri);
}
});
}
#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);
}
}
This should be working.By the way.Don't rush into android like this...you've got to learn a few things about how it works before you can play with it.Try to check the documentation and play with all that android offers.It's actually fun.It was for me and it still is as I've got to learn a lot ,still.

you call the method game() when you click the edittext "editText", and this will change the textview. If you want to change the value of the textview by clicking button "button", i think you just need to move the game() method to the Button field:
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="ok"
android:id="#+id/button"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:onClick="game" />

How to make TextView Visibile On ButtonClick()?

I want it so that when I click a button the text will become visible.
I failed.
Please, help me
Loveandriod.java
package com.example.farjad.andriodlove;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
public class LoveAndriod extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_love_andriod);
}
public void onLoveButtonClicked(View view){
TextView.setVisibility(R.id.haikowtext);
TextView haikotext=findViewById(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.menu_love_andriod, 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);
}
}
and the activity log is below;
activity.love_andriod.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=".LoveAndriod">
<TextView android:text="#string/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/haikowtext"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="123dp"
android:visibility="invisible" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/love_button_text"
android:id="#+id/button"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:onClick="onLoveButtonClicked"/>
</RelativeLayout>
How can I sove that?
I am a beginner with Android Studio.

Try this:
TextView haikotext = (TextView)findViewById(R.id.haikowtext);
haikotext.setVisibility(View.VISIBLE);

#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_love_andriod);
TextView tv = (TextView)findViewById(R.id.haikowtext);
}
public void onLoveButtonClicked(View view){
tv.setVisibility(View.VISIBLE);
}

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.

Starting a new Activity-Application stops working

I am trying to build a simple app for a school assignment. When the user clicks on the image button a new view opens up with a picture of the image.However whenever a user clicks on the image in my application the it stops. The logcat error says says at android view.view.onclick, but I can't see where the mistake is. Thanks in advance.
main_activity.java
package com.example.kids;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ImageButton;
public class MainActivity extends Activity {
#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;
}
public void apple(ImageButton buttona){
Intent intent = new Intent(this, Apple.class);
startActivity(intent);
}
public void banana(ImageButton buttonb){
Intent intent = new Intent(this, Banana.class);
startActivity(intent);}
public void strawberry(ImageButton buttons){
Intent intent = new Intent(this, Strawberry.class);
startActivity(intent);
}}
Apple.java
package com.example.kids;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class Apple extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_apple);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.apple, menu);
return true;
}
}
Activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="100"
android:orientation="vertical" >
<TextView
android:id="#+id/textView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_weight="9.93"
android:text="Pick a fruit"
android:textAppearance="?android:attr/textAppearanceLarge" />
<ImageView
android:id="#+id/imageView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="30"
android:src="#drawable/applebudget"
android:onClick="apple"
/>
<ImageView
android:id="#+id/imageView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="30"
android:src="#drawable/bananabudget"
android:onClick="banana"
/>
<ImageView
android:id="#+id/imageView3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="30"
android:src="#drawable/strawberrybudget"
android:onClick="strawberry"
/>
</LinearLayout>

Change the method signatures of onClick() methods:
public void apple(View buttona){}
public void banana(View buttonb){}
public void strawberry(View buttons){}
And you are done.