在Android中滑动刷新后如何保持UI更改

Question

So, I have this getView method in my CommentsAdapter class, and it basically allows the user to upvote or downvote a comment in the comments section while displaying the upvote count. I am able to upvote (and undo the upvote) with the corresponding UI change (blue button for un-upvoted and orange for upvoted).

However, once I refresh the screen, the button will always revert to blue regardless if it was upvoted or not and the vote count back to the original count. I did check the database and the correct upvote count and action were logged. Any tips?

public class CommentsAdapter extends ArrayAdapter<Post> { 
  private int layout;
  private Context context;
  private ArrayList<Post> postList = new ArrayList<>();

  public CommentAdapter(@NonNull Context cont, @LayoutRes int textViewResourceId, @NonNull ArrayList<Post> objects) {
    super(cont, textViewResourceId, objects);
    layout = textViewResourceId;
    context = cont;
    postList = objects;
  }

  public View getView(final int position, @Nullable View convertView, @NonNull ViewGroup parent) {
      final ViewHolder v;
      final Post comment = postList.get(position);
      final String mimeType = "text/html";
      final String encoding = "UTF-8";
      final SharedPreferences prefs = context.getSharedPreferences("user_session", MODE_PRIVATE);
      final String sessionKey = prefs.getString("session_key", "");
      String htmlData = "<link rel=\"stylesheet\" type=\"text/css\" href=\"comments.css\" />" + comment.content;

      if (convertView == null) {
          v = new ViewHolder();
          LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
          convertView = inflater.inflate(layout, parent, false);

          v.upvotedIcon = convertView.findViewById(R.id.navbar_upvoted_icon);
          v.upvoteIcon = convertView.findViewById(R.id.navbar_upvote_icon);
          v.upvotedText = convertView.findViewById(R.id.navbar_upvoted_text);
          v.upvoteText = convertView.findViewById(R.id.navbar_upvote_text);

          v.upvoteButton = convertView.findViewById(R.id.navbar_upvote_button);
          v.upvotedButton = convertView.findViewById(R.id.navbar_upvoted_button);

          v.upvotedIcon.setTypeface(fontAwesome);
          v.upvoteIcon.setTypeface(fontAwesome);
          v.upvotedText.setTypeface(opensans);
          v.upvoteText.setTypeface(opensans);

          convertView.setTag(v);
      } else {
          v = (ViewHolder) convertView.getTag();
      }

      v.upvoteText.setText(String.format(Locale.ENGLISH, "%d", comment.stats.upvotes));
      v.upvotedText.setText(String.format(Locale.ENGLISH, "%d", comment.stats.upvotes + 1));

      if (comment.hasReacted) {
          v.upvoteButton.setVisibility(View.GONE);
          v.upvotedButton.setVisibility(View.VISIBLE);
      } else {
          v.upvotedButton.setVisibility(View.GONE);
          v.upvoteButton.setVisibility(View.VISIBLE);
      }

      v.upvoteButton.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              setButtonState(true, comment, v);
              Call<JsonObject> call = MyApi.endpoint().upVotePost(sessionKey, comment.id);
              call.enqueue(new Callback<JsonObject>() {
                  @Override
                  public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
                      if(response.code() != 200) {
                          // show upvote icon
                          setButtonState(false, comment, v);
                          Toast.makeText(context, "Cannot upvote for the moment, try again later.", Toast.LENGTH_SHORT).show();
                      }
                  }

                  @Override
                  public void onFailure(Call<JsonObject> call, Throwable t) {
                      // show upvote icon
                      setButtonState(false, comment, v);
                      Toast.makeText(context, "Cannot connect to the server, try again later.", Toast.LENGTH_SHORT).show();
                  }
              });
          }


      });

      v.upvotedButton.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              // show upvote icon
              setButtonState(false, comment, v);
              Call<JsonObject> call = MyApi.endpoint().downVotePost(sessionKey, comment.id);
              call.enqueue(new Callback<JsonObject>() {
                  @Override
                  public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
                      if(response.code() != 200) {
                          // show upvoted icon
                          setButtonState(true, comment, v);
                          Toast.makeText(context, "Cannot undo your upvote for the moment, try again later.", Toast.LENGTH_SHORT).show();
                      }
                  }

                  @Override
                  public void onFailure(Call<JsonObject> call, Throwable t) {
                      // show upvoted icon
                      setButtonState(true, comment, v);
                      Toast.makeText(context, "Cannot connect to the server, try again later.", Toast.LENGTH_SHORT).show();
                  }
              });
          }
      });

      return convertView;
  }
}

Answer 1

You should add a property to your model that is a status, with values like "upvoted", "downvoted", etc., or {empty string}. Then when your data is acted on set that status accordingly. Then when the data is reloaded check your model for that status and display using the proper icon for each status. (I am simply using strings for the status values, but you could do something more elegant).

Edit:

As several users have pointed out, make sure that you are calling notifyDataSetChanged after modifying you database values. Also if you are pulling your data from a remote server, make sure you have updated the upvote/downvote values before you do the reload, (or at least properly merge remote data with your local data).