我遇到了错误“未为MainActivity类型定义方法getSupportActionBar()”importandroid.app.FragmentTransaction;importandroid.os.Bundle;importandroid.support.v7.app.ActionBar;importandroid.support.v7.app.ActionBar.Tab;importandroid.support.v4.app.Fragment;importandroid.support.v4.app.FragmentActivity;importandroid.suppo