[Solved] My app crashes when I change the background color

package com.withur.facttest;

import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    // Declare our View variables
    private FactBook factBook = new FactBook();

    private RelativeLayout relativeLayout;
    private TextView factTextView;
    private Button showFactButton;

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

        relativeLayout = findViewById(R.id.mainLayout);
        factTextView = findViewById(R.id.factTextView);
        showFactButton = findViewById(R.id.showFactButton);
        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //Update the screen with a new fact
                relativeLayout.setBackgroundColor(Color.RED);
                factTextView.setText(factBook.getFact());

            }
        };
        showFactButton.setOnClickListener(listener);
    }
}