Error:(79, 38) 错误: 不兼容的类型: BaseFragment无法转换为Fragment 是什么原因？大神指教

package com.example.administrator.fragmenttest;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.widget.RadioGroup;

import com.example.administrator.fragmenttest.base.BaseFragment;
import com.example.administrator.fragmenttest.fragment.OtherFragment;
import com.example.administrator.fragmenttest.fragment.Sgigement;
import com.example.administrator.fragmenttest.fragment.WenxueFragment;
import com.example.administrator.fragmenttest.fragment.XiaoshuoFragment;

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

public class MainActivity extends FragmentActivity {
    List<BaseFragment> mBaseFragment;
    RadioGroup rg_main;
    private int position;

    private Fragment mContext;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //初始化view
        initView();
        //初始化Fragment
        initFragment();
        //设置监听
        setListener();
    }

    private void setListener() {
        rg_main.setOnCheckedChangeListener(new MyOnCheckedChangeListener());
        rg_main.check(R.id.rb_sanwen);
    }

    private void initFragment() {
        mBaseFragment = new ArrayList<>();
        mBaseFragment.add(new WenxueFragment());
        mBaseFragment.add(new Sgigement());
        mBaseFragment.add(new XiaoshuoFragment());
        mBaseFragment.add(new OtherFragment());
    }
    private void initView() {
        setContentView(R.layout.activity_main);
        rg_main = (RadioGroup) findViewById(R.id.rg_main);
    }

    private class MyOnCheckedChangeListener implements RadioGroup.OnCheckedChangeListener {
        @Override
        public void onCheckedChanged(RadioGroup radioGroup, int checkId) {
            switch (checkId) {
                case R.id.rb_sanwen:
                    position = 0;
                    break;
                case R.id.rb_shige:
                    position = 1;
                    break;
                case R.id.rb_xiaoshuo:
                    position = 2;
                    break;
                case R.id.rb_other:
                    position = 3;
                    break;

                default:
                    position = 0;
                    break;
            }
            //根据位置得到对应的Framgent
            BaseFragment to = getFragment();
            //替换
            switchFragment(mContext,to);
        }

        private void switchFragment(Fragment from, Fragment to) {
            if (from != to) {
                //才切换
                mContext = to;
                FragmentManager fm = getSupportFragmentManager();
                
                //开启事务
                FragmentTransaction transaction = fm.beginTransaction();
                if (!to.isAdded()) {
                    if (from != null) {
                        transaction.hide(from);
                    }
                    if (to != null) {
                      transaction.add(R.id.f1_frame, to).commit();


                    }

                } else if (from != null) {
                    transaction.hide(to);
                }
                if (to != null) {
                    transaction.show(to).commit();

                }


            }
        }


        private BaseFragment getFragment() {
            BaseFragment fragment = mBaseFragment.get(position);
            return fragment;

        }
    }


}