Type mismatch: cannot convert from MainFragment to Fragment 报错

源码：

        FragmentTransaction mFragmentTranscation = getSupportFragmentManager().beginTransaction();
        Fragment mMainFragment = new MainFragment();//此行提示出错
        mFragmentTranscation.replace(R.id.container, mMainFragment);
        mFragmentTranscation.commit();

错误提示：无法将MainFragment (Fragment的子类)强制转换成Fragment

解决方法：

在原来的MainFragment中把

import android.app.Fragment;

更改为:

import android.support.v4.app.Fragment;