error: cannot find symbol variable viewpager ---Androidx

Question

I have the following code, the project is migrated to andoidx, R.id.viewpager returns can not find symbol variable viewpager SimpleFragmentPagerAdapter is a custom(an extention of) FragmentPagerAdapter and is working well

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;

public class MainActivity extends AppCompatActivity {

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

    // Set the content of the activity to use the activity_main.xml layout file
    setContentView(R.layout.activity_catagory);

    ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);

    // Create an adapter that knows which fragment should be shown on each page
    SimpleFragmentPagerAdapter adapter = new SimpleFragmentPagerAdapter(getSupportFragmentManager());

    // Set the adapter onto the view pager
    viewPager.setAdapter(adapter);


}

}