无法解析符号“ DataManager”

Question

我正在尝试将我的适配器与recycleview关联。错误发生在initializeDisplayContent（）方法中。这是我的代码

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class AnnouncementsFragment extends Fragment {
    View rootView;
    private AnnouncementRecyclerAdapter mAnnouncementRecyclerAdapter;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        rootView =  inflater.inflate(R.layout.fragment_announcements, container, false);

        return rootView;
    }

    private void initializeDisplayContent() {
        final RecyclerView recyclerAnnouncements = (RecyclerView) rootView.findViewById(R.id.list_announcements);
        final LinearLayoutManager announcementsLayoutManager = new LinearLayoutManager(getContext());
        recyclerAnnouncements.setLayoutManager(announcementsLayoutManager);

        List<Announcement> announcementsList = DataManager.getInstance().getAnnouncements();
    }

}

我有一个公告类，其中包含两个项目的getter和setter：

public class Announcement {
    private int id;
    private String announcementTitleText, announcementDetailsText;
    public Announcement(int id, String announcementTitleText, String announcementDetailsText) {
        this.id = id;
        this.announcementTitleText = announcementTitleText;
        this.announcementDetailsText = announcementDetailsText;
    }

    public int getId() {
        return id;
    }

    public void setId() {
        this.id =id;
    }