如何制作不同类型对象的ArrayList？

Question

我有两个 pojo 课程，即 PostFeed 和 SessionFeed

PostFeed.class

public class PostFeed implements Parcelable{

private int pid;
private int uid;
private String link;
private String title;
private String description;
private int up;
private int comment_count;
private String postPicUrl;
private Date dop;
private String user_name;
private String user_pic;
private String user_status;
private DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
//getters and setters
}

SessionFeed.class

public class SessionFeed implements Parcelable{
private String session_title;
private String session_image;
private String session_description;
private int session_id;
private String s_venue;
private String s_coordinator;
private String s_c_email;
private String s_c_phone;
private String resource_person;
private String rp_desg;
private String time_and_date;
private String address;
private String room;
private DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
private Date Dosp;
String user_name;
int uid;
String user_status;
String user_pic;
// getters and setters
}

我正在尝试创建一个从 MySqlite 数据库中搜索数据的搜索活动。每种类型都有两个单独的表，即两个不同数据库中的PostFeedTable 和SessionFeedTable。

在我的数据库操作类中，这就是我要返回的内容：

 public ArrayList<PostFeed> readPostForSearch(String searchText, DatabaseOperations dop){
    SQLiteDatabase sqLiteDatabase = dop.getReadableDatabase();
    ArrayList<PostFeed> newsFeedList = new ArrayList<>();
    String query ="select * from " + html_test_const.getTable_name() + " where " + html_test_const.getTitle() +" LIKE '%"+searchText+"%' OR "+ html_test_const.getDescription() + " LIKE '%"+searchText+"%'"+" order by date desc " +";";
    Cursor cursor = sqLiteDatabase.rawQuery(query,null);
    if (cursor != null && cursor.moveToFirst()) {
        L.m("loading entries " + cursor.getCount() + new Date(System.currentTimeMillis()));
        do {

            //create a new object and retrieve the data from the cursor to be stored in this object
            PostFeed postFeed = new PostFeed();
            postFeed.setTitle(cursor.getString(cursor.getColumnIndex(html_test_const.getTitle())));
            postFeed.setLink(cursor.getString(cursor.getColumnIndex(html_test_const.getLink())));
            postFeed.setDescription(cursor.getString(cursor.getColumnIndex(html_test_const.getDescription())));
            long dateOfPost = cursor.getLong(cursor.getColumnIndex(html_test_const.getDate()));
            postFeed.setDop(new java.sql.Date(dateOfPost));
            postFeed.setUser_name(cursor.getString(cursor.getColumnIndex(html_test_const.getUser_name())));
            postFeed.setPid(cursor.getInt(cursor.getColumnIndex(html_test_const.getSr_key())));
            postFeed.setUp(cursor.getInt(cursor.getColumnIndex(html_test_const.getUp_down())));
            postFeed.setComment_count(cursor.getInt(cursor.getColumnIndex(html_test_const.getComment_count())));
            postFeed.setUid(cursor.getInt(cursor.getColumnIndex(html_test_const.getUid())));
            postFeed.setPostPicUrl(cursor.getString(cursor.getColumnIndex(html_test_const.getPost_pic())));
            postFeed.setUser_pic(cursor.getString(cursor.getColumnIndex(html_test_const.getUser_pic())));
            postFeed.setUser_status(cursor.getString(cursor.getColumnIndex(html_test_const.getUser_status())));
            newsFeedList.add(postFeed);

        } while (cursor.moveToNext());
    }

    return newsFeedList;
}

这对于带有各个变量的会话数据库操作是相同的。

SearchActivity 包含一个回收器视图，其适配器采用 ArrayList 并设置该列表，该列表将进一步包含两种类型的行元素。

问题：如何创建一个包含这两种对象的arraylist，以及如何让recycler view显示arraylist中的这两种对象。

如果您需要更多说明，请告诉我。提前致谢。

Answer 1

我认为 nikka 的建议是正确的。改进它，为您的适配器使用以下类

public class Feed implements Parcelable{

    private PostFeed postFeed;
    private SessionFeed sessionFeed;

    public Feed(PostFeed feed){
        this.postFeed = feed;
    }

    public Feed(SessionFeed feed){
        this.sessionFeed = feed;
    }

    //returns true for session feed type
    public boolean isSessionFeed(){
        return sessionFeed!=null;
    }

    public SessionFeed getSessionFeed(){
        return sessionFeed;
    }

    public PostFeed getPostFeed(){
        return postFeed;
    }

}

然后在您的数据库辅助方法中，返回 Feed 对象列表。

public List<Feed> readPostForSearch(String searchText, DatabaseOperations dop){
    SQLiteDatabase sqLiteDatabase = dop.getReadableDatabase();
    List<Feed> newsFeedList = new ArrayList<>();
    ...
    if (cursor != null && cursor.moveToFirst()) {
        L.m("loading entries " + cursor.getCount() + new Date(System.currentTimeMillis()));
        do {
            PostFeed postFeed = new PostFeed();

            ...

            newsFeedList.add(new Feed(postFeed));

        } while (cursor.moveToNext());
    }

    return newsFeedList;
}

对 sessionFeeds 重复相同的操作，然后将此列表从数据库添加到适配器的列表中。设置视图时，使用isSessionFeed() 检查类型并相应地设置视图。希望对您有所帮助。

Answer 2

您已经实现了Parcelable interface，因此您可以创建此interface 的列表，该列表可用于存储implemented class object。

ArrayList<Parcelable> pList = new ArrayList<>();

Answer 3

由于两者之间似乎没有太多共同点，尽管名称相似，您不妨创建一个包含PostFeed 和SessionFeed 的新对象。

class FeedHolder implements Parcelable {

    private final List<PostFeed> postFeeds;
    private final List<SessionFeed> sessionFeeds;

    FeedHolder(@NonNull List<PostFeed> postFeeds,@NonNull List<SessionFeed> sessionFeeds) {
        this.postFeeds = postFeeds;
        this.sessionFeeds = sessionFeeds;
    }

    List<SessionFeed> getSessionFeeds() {
        return sessionFeeds;
    }

    List<PostFeed> getPostFeeds() {
        return postFeeds;
    }

    //If you're using this data in an adapter, knowing the total
    //size of both lists might be helpful.
    int getTotalFeedCount() {
        return postFeeds.size() + sessionFeeds.size();
    }

}

//...

List<SessionFeed> sessionFeeds = //whatever you do to populate your
//List of SessionFeeds...
List<PostFeed> postFeeds = //Same again.
FeedHolder feedHolder = FeedHolder(postFeeds, sessionFeeds);

Answer 4

public class Feeds implements Parcelable{

private PostFeed postFeed;
private SessionFeed sessionFeed;

Public Feeds(PostFeed postfeed, SessionFeed sessionfeed){
this.postFeed = postfeed
this.sessionFeed = sessionfeed
}
}

然后Feed的数组列表将解决问题。

还有

for(int i=0: i<postfeedArraylist.size; i ++)
    feedsArraylist.add( new Feeds(postfeedArraylist.get(i), null);

对 sessionfeedArraylist 也重复相同的 for 循环。