Android: Error when triggering fragment from within the fragment itself

Question

I'm trying to learn fragments on android and my code is not working. FragmentCustomAnimations contains MainActivity. What i want is the frame MainActivity to change when i push the button on MainActivity. The error message on logcat is Could not find a method sendMessage(View) in the activity class com.example.myfirstapp.FragmentCustomAnimations for onClick handler on view class android.widget.Button with id 'button1' Eventhough there is no function sendmessage in all my file. FYI, its working when i put the button on FragmentCustomAnimations. Is it impossible to use the button on fragment to trigger action to change the fragment itself?

Here is the code:

FragmentCustomAnimations.java

package com.example.myfirstapp;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class FragmentCustomAnimations extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_stack);

        if (savedInstanceState == null) {
            Fragment newFragment = InitialFragment.newInstance();
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.add(R.id.simple_fragment, newFragment).commit();
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }

    public static class InitialFragment extends Fragment {

        static InitialFragment newInstance() {
            InitialFragment f = new InitialFragment();

            Bundle args = new Bundle();
            f.setArguments(args);

            return f;
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);         
        }

        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View v = inflater.inflate(R.layout.activity_main, container, false);
            return v;
        }
    }
}

fragment_stack.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:padding="4dip"
    android:gravity="center_horizontal"
    android:background="@drawable/window2x"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <FrameLayout
            android:id="@+id/simple_fragment"
            android:layout_width="match_parent"
            android:layout_height="0px"
            android:layout_weight="1">
    </FrameLayout>

</LinearLayout>

MainActivity.java

package com.example.myfirstapp;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final Button inner = (Button) findViewById(R.id.button1);

        inner.setOnClickListener(this);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu items for use in the action bar
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main, menu);

        getActionBar().setDisplayShowHomeEnabled(false);

        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public void onClick(View v) {

        addFragmentToStack();

    }

    void addFragmentToStack() {

        Fragment newFragment = CountingFragment.newInstance();

        FragmentTransaction ft = getFragmentManager().beginTransaction();
        ft.setCustomAnimations(R.animator.fragment_slide_left_enter,
                R.animator.fragment_slide_left_exit,
                R.animator.fragment_slide_right_enter,
                R.animator.fragment_slide_right_exit);
        ft.replace(R.id.simple_fragment, newFragment);
        ft.addToBackStack(null);
        ft.commit();
    }

    public static class CountingFragment extends Fragment {

        static CountingFragment newInstance() {
            CountingFragment f = new CountingFragment();

            Bundle args = new Bundle();
            f.setArguments(args);

            return f;
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);         
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View v = inflater.inflate(R.layout.activity_display_message, container, false);
            return v;
        }
    }
}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="?android:attr/actionBarSize"    
    android:layout_gravity="center_vertical"
    tools:context=".MainActivity" >

    <EditText
        android:id="@+id/edit_message"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/edit_message"
        android:layout_gravity="center_vertical"
        android:inputType="textPersonName" >
        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/editTextEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/editTextEmail"
        android:inputType="textEmailAddress" />

    <EditText
        android:id="@+id/editTextPassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/editTextPassword"
        android:inputType="textPassword" />

    <Button
        android:id="@+id/button1"
        style="@style/CodeFont"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:background="@drawable/custom_button"
        android:text="@string/button_send" />

</LinearLayout>