Android分页库不会停止在recyclerview中加载项目

Question

我正在使用 Android 分页库...它的工作方式很奇怪 - 项目会无限加载，即使没有更多数据要加载也不会停止。

例如，我有 2 个项目要加载，而不是只加载 2 个项目并停止加载，它会不断重复加载 2 个项目...这是我所面临的 gif。

首先是我的仓库

CommentDataSource.java

注意 - 当我将“PAGE_SIZE”的值更改为“1”时，它似乎有效，但分页的整个目的都失败了，因为所有项目都是一次加载。 （我测试了更多项目）

public class CommentDataSource extends PageKeyedDataSource<Long, Comment> {
public static int PAGE_SIZE = 10;
public static long FIRST_PAGE = 1;

 public CommentDataSource(){
  }

 @Override
 public void loadInitial(@NonNull final LoadInitialParams<Long> params, @NonNull final 
 LoadInitialCallback<Long, Comment> callback) {
 RestApi restApi = RetrofitApi.create();

 Call<CommentResponse> call = restApi.getComments(FIRST_PAGE);

 call.enqueue(new Callback<CommentResponse>() {
        @Override
        public void onResponse(Call<CommentResponse> call, Response<CommentResponse> response) {
            CommentResponse commentResponse = response.body();
            if(commentResponse!=null){
                progress_bar.postValue(false);
                List<Comment> responseItems = commentResponse.getCommentResponses();
                callback.onResult(responseItems, null, FIRST_PAGE + 1);
            }
        }

   @Override
public void loadBefore(@NonNull final LoadParams<Long> params, @NonNull final LoadCallback<Long, Comment> callback) {
    RestApi restApi = RetrofitApi.create();

    Call<CommentResponse> call = restApi.getComments(params.key);

    call.enqueue(new Callback<CommentResponse>() {
        @Override
        public void onResponse(Call<CommentResponse> call, Response<CommentResponse> response) {
            CommentResponse commentResponse = response.body();
            if(commentResponse!=null){
                progress_bar.postValue(false);
                List<Comment> responseItems = commentResponse.getCommentResponses();
                long key;
                if(params.key > 1){
                    key = params.key - 1;
                }
                else {
                    key = 0;
                }
                callback.onResult(responseItems, key);
            }
        }
    });

}

@Override
public void loadAfter(@NonNull final LoadParams<Long> params, @NonNull final LoadCallback<Long, Comment> callback) {

    RestApi restApi = RetrofitApi.create();

    Call<CommentResponse> call = restApi.getComments(params.key);

    call.enqueue(new Callback<CommentResponse>() {
        @Override
        public void onResponse(Call<CommentResponse> call, Response<CommentResponse> response) {
            CommentResponse commentResponse = response.body();
            if(commentResponse!=null){
                progress_bar.postValue(false);
                List<Comment> responseItems = commentResponse.getCommentResponses();
                callback.onResult(responseItems, params.key + 1);
            }
        }

    });
 }
}

这是我的ViewModel

CommentViewModel.java

public class CommentViewModel extends ViewModel {
public CommentViewModel(){
    CommentDataFactory commentDataFactory = new CommentDataFactory();
    liveDataSource = commentDataFactory.commentLiveDataSource;

    progressBar = Transformations.switchMap(liveDataSource, CommentDataSource::getProgressBar);

    PagedList.Config config = new PagedList.Config.Builder()
            .setEnablePlaceholders(false)
            .setPageSize(CommentDataSource.PAGE_SIZE)
            .build();

    commentPagedList = new LivePagedListBuilder<>(commentDataFactory, config).build();
}


public LiveData<PagedList<Comment>> getCommentData(){
    return commentPagedList;
}

public void getRefreshedData(){
    getCommentData().getValue().getDataSource().invalidate();
   } 
 }

这是我的PHP 数据库查询代码，它以JSON 格式返回。

get_cmets.php

<?php
  $limit = 10;

  //find out how many rows are in the table
  $sql = "SELECT count(*) FROM comments"; 
  $result = $conn->prepare($sql); 
  $result->execute();
  $total = $result->fetchColumn();
  $totalpages = ceil($total/$limit);

  if (isset($_GET['page']) && is_numeric($_GET['page'])) {
  $currentpage =  $_GET['page'];
  } else {
  // default page num
  $currentpage = 1;
  }

if ($currentpage > $totalpages) {
 // set current page to last page
 $currentpage = $totalpages;
 }

 // if current page is less than first page... 
if ($currentpage < 1) {
  $currentpage = 1; 
 } 

 //the offset of the list, based on current page 
 $offset = ($currentpage - 1) * $limit;


  $stmt = "SELECT * FROM comments ORDER by id DESC LIMIT $offset, $limit";
  $result = $conn->prepare($stmt); 
  $result->execute();

  $response = array(); 

  while ($row = $result->fetch()) {

  $temp['id']=$row['id'];
  $temp['image_id']=$row['image_id'];
  $temp['comment']=$row['comment'];
  $temp['comment_by']=$row['comment_by'];
  $temp['date_posted']=$row['date_posted'];

  array_push($response, $temp);

  $obj = (object) [ 
 'data' =>  $response
  ];

 }
echo json_encode($obj); 
?>

这些是我觉得需要的代码...我没有添加适配器和工厂，但如果需要，我可以添加其他代码...有人请帮忙，因为我已经做了几天了.. .

"

Answer 1

我想我知道为什么它会一次又一次地加载，原因如下：

在CommentDataSource 的loadInitial() 中，您将在onReponse() 的callback.onResult(responseItems, null, FIRST_PAGE + 1); 行中传递FIRST_PAGE + 1，这意味着在loadAfter() 中FIRST_PAGE + 1 作为第2 页传递restApi.getComments(params.key) 行，但您的数据库中不存在第 2 页，如果您的 php 中的页码大于 1，则您正在设置相同的页码

if ($currentpage > $totalpages) {
 // set current page to last page
 $currentpage = $totalpages;
 }

所以你一次又一次地调用第 1 页。在loadAfter() 中，您一次又一次地调用第 1 页。