activity_main cannot be resolved or is not a fiel

i keep receiving that error . here is my Main activity package com.example.magicball;

import android.R; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.View; import android.widget.Button; import android.widget.TextView;

public class MainActivity extends Activity { private crystallball mcrystallball = new crystallball(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_list_item); final TextView answerLabel = (TextView) findViewById(R.id.textView1); Button getAnswerButton = (Button) findViewById(R.id.button1); getAnswerButton.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View arg0) {
    String answer = mcrystallball.getAnAnswer();

        answerLabel.setText(answer);
    }
});
}

@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;
}

} Maybe it has something to do with my layout, here is the code
<TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:textSize="32sp" />

<Button
    android:id="@+id/button1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="22dp"
    android:text="tell me" />