FragmentManager支持库的类型不兼容

获取不兼容类型的FragmentManager的持续错误。需要支持库才能正常工作,但无法弄清楚。Android Studio表示,它需要支持导入,但找到了androidx导入。

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import androidx.appcompat.app.AppCompatActivity;


public class CrimeActivity extends AppCompatActivity
{

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

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);

        if(fragment == null)
        {
            fragment = new CrimeFragment();
            fm.beginTransaction()
                    .add(R.id.fragment_container, fragment)
                    .commit();


        }
    }
}```