Adding installed widgets to Android activity

I'm using Android Studio to create an Android Launcher app.

I'm trying to add a feature that allows the user to select an installed widget and place it on my launcher. Similar to what most launchers on the play store provide.

My code is currently is giving me cannot resolve symbol errors on appWidgetHost and appWidgetManager.

I've had a look on SO and Google on how to achieve this but I'm still confused on how to get this to work and how to correct my code.

Here's my code:

package com.example.widgettest;

import android.app.Activity;
import android.appwidget.AppWidgetHostView;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProviderInfo;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;

import java.util.ArrayList;
import java.util.List;


public class MainActivity extends Activity {

    Button widgetButton;
    // APPWIDGET_HOST_ID is any number you like
    appWidgetManager = AppWidgetManager.getInstance(this);
    appWidgetHost = new AppWidgetHost(this, 1);
    AppWidgetProviderInfo newAppWidgetProviderInfo = new AppWidgetProviderInfo();

    // Get an id
    int appWidgetId = appWidgetHost.allocateAppWidgetId();

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

    }

   public void createwidget(){
       // Get the list of installed widgets
       List<AppWidgetProviderInfo> appWidgetInfos = new ArrayList<AppWidgetProviderInfo>();
       appWidgetInfos = appWidgetManager.getInstalledProviders();



// Create Widget
       AppWidgetHostView hostView = appWidgetHost.createView(this, appWidgetId, newAppWidgetProviderInfo);
       hostView.setAppWidget(appWidgetId, newAppWidgetProviderInfo);

// Add it to your layout
       RelativeLayout rl = (RelativeLayout) findViewById(R.id.rl);
       rl.addView(hostView);
    }

    public void addwidgetButtonListener() {

        widgetButton = (Button) findViewById(R.id.button);
        widgetButton.setOnClickListener(new View.OnClickListener() {

            public void onClick(View view) {
createwidget();
            }
        });
    }
}