Unfortunately projects has stopped: onClickListener

Question

When I open the app it says "Unfortunately program has stopped". So i can't use the application. How can i repair this?

This is my code: I put the incorrect code, this is the real code, same error

package com.RaulLara.projects;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
import android.app.Activity;
import android.widget.TextView;
import android.view.View.OnClickListener;
import android.widget.Button;



public class MainActivity extends ActionBarActivity {

Button btn = (Button) findViewById(R.id.btn1);
@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_main);
    setupmybutton();
    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment())
                .commit();
    }

}
    private void setupmybutton() {
        btn.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {

        }
    });
}
    @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;
    }

    /**
     * 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;
            }
        }


}

This is my fragment_main:

<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.RaulLara.projects.MainActivity$PlaceholderFragment" >

        <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="79dp"
            android:text="Large Text"
            android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
            android:id="@+id/btn1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/textView1"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="56dp"
            android:text="@string/button" />

    </RelativeLayout>

And this is my AndroidManifest:

    <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.RaulLara.projects"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        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.RaulLara.projects.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>
    </application>

</manifest>

Answer 1

You are using wrong id for the button. This is causing a NULL mybutton1 to be returned and hence a null pointer exception.

Change

  Button mybutton1 = (Button) findViewById(R.id.button1);

to

  Button mybutton1 = (Button) findViewById(R.id.btn1);

Good Luck

Answer 2

Since you are setting up your button in OnCreate of the MainActivity make sure your declare your btn1 in activity_main and not in the fragment's layout fragment_main