Develop Reference

Android can't find my OnClick method

I have an issue with this botton, when is clicked the app send a message "ImageButton has stopped". I think it's something dumb, but I just started coding. Details of my code are below.
LogCat:
12-13 21:01:56.659 1075-1075/com.example.christian.imagebutton E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.christian.imagebutton, PID: 1075
java.lang.IllegalStateException: Could not find method llamar(MainActivity)(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatImageButton with id 'boton1'
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:327)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:284)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Main Activity
package com.example.christian.imagebutton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private TextView tv1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv1=(TextView)findViewById(R.id.tv1);
}
public void llamar(View view){
tv1.setText("Llamando");
}
}
And the layout is:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
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.christian.imagebutton.MainActivity">
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:srcCompat="#mipmap/telefono"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:id="#+id/boton1"
android:onClick="llamar(MainActivity)" />
<TextView
android:text="TextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/boton1"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="22dp"
android:id="#+id/tv1" />
</RelativeLayout>

android:onClick="llamar"
Shouldn't it be like this?

Android just implements the OnClickListener for you when you define the android:onClick="someMethod" attribute.
Those two code snippets are totally the same but just implemented in two different ways.
Code Implementation
Button btn = (Button) findViewById(R.id.mybutton);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
llamar(v);
}
});
// some more code
public void llamar(View v) {
// does something very interesting
}
Above is a code implementation of an OnClickListener. And now the XML implementation.
XML Implementation
<?xml version="1.0" encoding="utf-8"?>
<!-- layout elements -->
<Button android:id="#+id/mybutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Click me!"
android:onClick="llamar" />
<!-- even more layout elements -->
Now in the background Android does nothing else than the Java code calling your method on a click event.
Note that with the XML above, Android will look for the onClick method llamar() only in the current Activity. This is important to remember if you are using fragments, since even if you add the XML above using a fragment, Android will not look for the onClick method in the .java file of the fragment used to add the XML.

Android Studio - Dynamic Fragment crashing App

I am trying to link a Fragment, RecycleView and CardView using a variation of the tutorial found on:
http://www.treyrobinson.net/blog/android-l-tutorials-part-3-recyclerview-and-cardview/
Unfortunately my app crashes with the following error message:
"java.lang.IllegalStateException: RecyclerView has no LayoutManager"
I am fairly new with Android development. I tried to find similar issues on Stackoverflow but am unable to find the issue. Any help would be greatly appreciated!
Layout of the main activity: "activity_library.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"
tools:context=".LibraryActivity">
<android.support.v7.widget.RecyclerView
android:id="#+id/library_activity_recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".LibraryActivity"
/>
</RelativeLayout>
The main activity class "LibraryActivity.java":
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
public class LibraryActivity extends AppCompatActivity{
private static final String TAG = LibraryActivity.class.getSimpleName();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); /**Create the activity and populate the savedInstanceState if the activity existed but has been destroyed (otherwise savedInstanceState will return 'null'*/
setContentView(R.layout.activity_library); /** Call to the XML layout library which display the activity */
if (savedInstanceState != null) {
// Restore value of members from saved state
} else {
// Probably initialize members with default values for a new instance
}
try {
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
BooksFragment bookFragment = new BooksFragment();
fragmentTransaction.add(R.id.library_activity_recycler_view,bookFragment);
/*The line below is the one generating the error - java.lang.IllegalStateException: RecyclerView has no LayoutManager*/
fragmentTransaction.commit();
}
catch(Exception e){
Log.d(TAG,"[ERROR] " + e.getMessage());
}
}
}
The layout of the fragment "fragment_books.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" >
<android.support.v7.widget.RecyclerView
android:id="#+id/Book_Recycler_View"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>
</LinearLayout>
And the fragment class:
import android.app.Fragment;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class BooksFragment extends Fragment {
public BooksFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.activity_library, container, false);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
RecyclerView bookRecycler = (RecyclerView) v.findViewById(R.id.library_activity_recycler_view);
bookRecycler.setLayoutManager(layoutManager);
BookRecyclerViewAdapter adapter = new BookRecyclerViewAdapter();
bookRecycler.setAdapter(adapter);
/*In the line below should we return the view 'v' or the RecyclerView 'bookRecycler'??*/
return bookRecycler;
}
}
As I said I am fairly new to Android and therefore apologies if my code contains quite a few errors. Thanks for your help!
For reference the complete error log:
04-18 14:04:52.323 11225-11225/com.wldtaster.tellmeastory E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.wldtaster.tellmeastory, PID: 11225
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wldtaster.tellmeastory/com.wldtaster.tellmeastory.LibraryActivity}: java.lang.IllegalStateException: RecyclerView has no LayoutManager
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.IllegalStateException: RecyclerView has no LayoutManager
at android.support.v7.widget.RecyclerView.generateLayoutParams(RecyclerView.java:3393)
at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
at com.wldtaster.tellmeastory.BooksFragment.onCreateView(BooksFragment.java:23)
at android.app.Fragment.performCreateView(Fragment.java:2053)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.app.BackStackRecord.run(BackStackRecord.java:834)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
at android.app.Activity.performStart(Activity.java:6005)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2288)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
at android.app.ActivityThread.access$800(ActivityThread.java:151) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5254) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

You must return the view ie. v in the onCreateView method of the Fragment inherited class.

Nested Fragments (multi-pane in tab)

i have problems to use a fragment in a fragment. The first fragment is a tab view an in one tab i want to have a multi-pane Layout like this:
The error is:
android.view.InflateException: Binary XML file line #8: Error
inflating class fragment
The tab fragment (SettingsFragmentBox):
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class SettingsFragmentBox extends Fragment implements SettingsFragmentBoxList.OnItemSelectedListener{
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_settings_box, container, false);
return rootView;
}
public void onBoxSelect(int id) {
SettingsFragmentBoxDetail fragment = (SettingsFragmentBoxDetail) getFragmentManager().findFragmentById(R.id.box_detail);
if (fragment != null && fragment.isInLayout()) {
fragment.setText(id);
} else {
Intent intent = new Intent(getActivity(),SettingsActivityBoxDetail.class);
intent.putExtra(SettingsActivityBoxDetail.EXTRA_ID, id);
startActivity(intent);
}
}
}
The xml (fragment_settings_box.xml):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<fragment
android:id="#+id/box_list"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
class="de.resper.e2cast.SettingsFragmentBoxList"
tools:layout="#layout/fragment_settings_box_list">
</fragment>
<fragment
android:id="#+id/box_detail"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="2"
class="de.resper.e2cast.SettingsFragmentBoxDetail"
tools:layout="#layout/fragment_settings_box_detail">
</fragment>
</LinearLayout>

Usually this is done using fragments in ACTIVITIES, not in other fragments. Are you sure you really want fragments in other fragments ?
The picture you are referring to is by the way showing this scenario (ACTIVITIES contain fragment A or B).

You should read http://developer.android.com/training/multiscreen/screensizes.html to handle different screensizes. There is an example with a layout containt two fragments in it. Also learn how to adapt to it by reading this http://developer.android.com/training/multiscreen/adaptui.html

Fragment doesn't work

I have main layout like this
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/btn_showdetails"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:layout_marginLeft="110dip"
android:layout_marginTop="15dip"
android:text="Show Details" />
</LinearLayout>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
android:id="#+id/my_parent_layout"
>
</LinearLayout>
</LinearLayout>
am trying to call another activity in the my_parent_layout using this class
package com.appnetics;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.Button;
public class FragmenttestActivity extends FragmentActivity {
Button LogIn = null ;
final FragmentManager fragmentManager = getSupportFragmentManager() ;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
LogIn = (Button) findViewById(R.id.btn_showdetails);
LogInEvent() ;
}
public void LogInEvent(){
LogIn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
details fragment = new details();
fragmentTransaction.add(R.id.my_parent_layout, fragment);
fragmentTransaction.commit();
}
});
}
}
the details layout is :
<?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/date_time_label"
android:layout_centerVertical="true"
android:layout_marginLeft="200dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="32dp"
android:textStyle="bold"
android:text="time_label"
/>
<TextView
android:id="#+id/last_view_time"
android:layout_toRightOf="#+id/date_time_label"
android:layout_alignBaseline="#+id/date_time_label"
android:layout_marginLeft="8dip"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="32dp"
/>
</LinearLayout>
and the layout code is
/* $Id: $
*/
package com.appnetics;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
/**
* DateTime
*/
public class details extends Fragment {
private static String getDateTimeString(Date time) {
return new SimpleDateFormat("d MMM yyyy HH:mm:ss")
.format(time);
}
private final String time = getDateTimeString(new Date());
/** #see android.app.Fragment#onCreateView(android.view.LayoutInflater, android.view.ViewGroup, android.os.Bundle) */
#Override
public View onCreateView(
LayoutInflater inflater,
ViewGroup container,
Bundle b)
{
View view = inflater.inflate(
R.layout.details,
container,
false); //!!! this is important
((TextView) view.findViewById(R.id.last_view_time))
.setText(time);
return view;
}
}
the problem is that when click the button, nothing appear , any idea what's wrong in my code

Lets start!
On your details XML:
android:layout_toRightOf="#+id/date_time_label"
android:layout_alignBaseline="#+id/date_time_label"
this two tags are for relative layouts, the parent of the layouts must be of relative type in order to work.
android:layout_centerVertical="true"
This tag is also incorrect, if you want to center the text in the textview you can use two ways or wrap content in textView and set center in its parent or use:
android:gravity="right"
android:width="fill_parent"
This will be the detail_fragment.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/date_time_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="32dp"
android:textStyle="bold"
android:text="time_label"
/>
<TextView
android:id="#+id/last_view_time"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="right"
android:text="view time"
android:textSize="32dp" />
</LinearLayout>
On your main.xml you declare the schema lots of times! should be declared once on your root layout.
LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
So the main.xml will be...
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center_horizontal"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/hello" />
<Button
android:id="#+id/add_fragment"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button" />
<LinearLayout
android:id="#+id/fragment_holder"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
</LinearLayout>
</LinearLayout>
The fragment is an element that is declared in its class and apply its xml.
public class DetailsFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment, container, false);
}
}
And in the main activity add it to the holder layout:
public class FragmentSimpleTestActivity extends FragmentActivity {
private Button addFragment;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final FragmentManager fragmentManager = getSupportFragmentManager();
addFragment = (Button) findViewById(R.id.add_fragment);
addFragment.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
DetailsFragment fragment = new DetailsFragment();
fragmentTransaction.add(R.id.fragment_holder,fragment, "MY_FRAG");
fragmentTransaction.commit();
}
});
}
}
Its important that fragmentTransaction.add has parameters
1: the id of the view to hold the fragment.
2: the fragment object.
3: a tag that is used to find the fragments in the stack.
and thats all :)
Enjoy your fragments! you can also set animations when adding or removing it.

onCreateView()
The system calls this when it's time for the fragment to draw its user interface for the first time. To draw a UI for your fragment, you
must return a View from this method that is the root of your
fragment's layout. You can return null if the fragment does not
provide a UI.
Call OnCreateView in your fragment class
return inflater.inflate(R.layout.fragmentlayout, container, false);

I had a similar problem, when fragment wasn't showing up. The problem was that I removed AndroidAnnotations, but forgot to move the code from onViewCreated and onCreate methods to the onCreateView. I found this mistake by comparing the code of two fragments - one, that was showing up and the other that wasn't. So, if you have similar problems, try to check the code of fragments. It may not show any errors at first glance, but will not still work or show up because of those errors.
Particularly, check that you have this method and that you inflate a view:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.your_fragment_layout, container, false);
return v;
}

Difficulties with basic fragment layout

I'm trying to get my head around fragments in order to have my apps prepped for ICS.
I have the following files to just get the most basic fragment app you can have. It should have this when launched: One Fragment Layout with a text view "Fragment 1" and next to it another Fragment Layout with "Fragment2".
My package name is com.mwerner.fragments
My files are:
FragmentsActivity.java
ExamplesFragment.java
ExamplesFragment2.java
examples_fragment.xml
examples_fragment2.xml
main.xml
The code for FragmentsActivity.java is:
package com.mwerner.fragments;
import android.app.Activity;
import android.os.Bundle;
public class FragmentsActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
ExamplesFragment.java
package com.mwerner.fragments;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class ExamplesFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.examples_fragment, container, false);
}
}
ExamplesFragment2.java
package com.mwerner.fragments;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class ExamplesFragment2 extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.examples_fragment2, container, false);
}
}
The examples_fragment.xml files just have a linear layout with a textview in it...
Here is the code for the main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<fragment
class="com.mwerner.fragments$ExamplesFragment"
android:id="#+id/list"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="fill_parent"
/>
<fragment
class="com.mwerner.fragments$ExamplesFragment2"
android:id="#+id/viewer"
android:layout_weight="2"
android:layout_width="0dp"
android:layout_height="fill_parent" />
</LinearLayout>
The app crashes on startup with the error
11-07 18:12:12.519: E/AndroidRuntime(696): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mwerner.fragments/com.mwerner.fragments.FragmentsActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
Can you please tell me what is wrong here? I pretty much copied / pasted the code from the google developers page for fragments.

You defined the path to your fragments incorrectly in your layout xml. Correct the class attributes. Try this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<fragment
class="com.mwerner.fragments.ExamplesFragment"
android:id="#+id/list"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="fill_parent"
/>
<fragment
class="com.mwerner.fragments.ExamplesFragment2"
android:id="#+id/viewer"
android:layout_weight="2"
android:layout_width="0dp"
android:layout_height="fill_parent" />
</LinearLayout>

Try extending FragmentActivity
public class FragmentsActivity extends FragmentActivity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}

When I was writing my first program on Fragments using I incurred same error. Instead of extending "Activity" extend "FragmentActivity" in your launcher activity.