Recycler View无限滚动无法正常工作

Question

我从TMDB获取数据并在回收站视图中显示它。我想使用无限滚动回收器视图，所以我看到了一些教程并实现了它。问题是，在第一次加载后，在滚动前5个元素后，整个数据将使用新数据刷新。我该如何解决这个问题？

EndlessRecyclerViewScrollListener.java

public abstract class EndlessRecyclerViewScrollListener extends RecyclerView.OnScrollListener {
/ The minimum amount of items to have below your current scroll position
// before loading more.
private int visibleThreshold = 15;
// The current offset index of data you have loaded
private int currentPage = 1;
// The total number of items in the dataset after the last load
private int previousTotalItemCount = 0;
// True if we are still waiting for the last set of data to load.
private boolean loading = true;
// Sets the starting page index
private int startingPageIndex = 1;

RecyclerView.LayoutManager mLayoutManager;

public EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
}

public EndlessRecyclerViewScrollListener(GridLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
    visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
}

public EndlessRecyclerViewScrollListener(StaggeredGridLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
    visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
}

public int getLastVisibleItem(int[] lastVisibleItemPositions) {
    int maxSize = 0;
    for (int i = 0; i < lastVisibleItemPositions.length; i++) {
        if (i == 0) {
            maxSize = lastVisibleItemPositions[i];
        }
        else if (lastVisibleItemPositions[i] > maxSize) {
            maxSize = lastVisibleItemPositions[i];
        }
    }
    return maxSize;
}

// This happens many times a second during a scroll, so be wary of the code you place here.
// We are given a few useful parameters to help us work out if we need to load some more data,
// but first we check if we are waiting for the previous load to finish.
@Override
public void onScrolled(RecyclerView view, int dx, int dy) {
    int lastVisibleItemPosition = 0;
    int totalItemCount = mLayoutManager.getItemCount();

    if (mLayoutManager instanceof StaggeredGridLayoutManager) {
        int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) mLayoutManager).findLastVisibleItemPositions(null);
        // get maximum element within the list
        lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions);
    } else if (mLayoutManager instanceof GridLayoutManager) {
        lastVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findLastVisibleItemPosition();
    } else if (mLayoutManager instanceof LinearLayoutManager) {
        lastVisibleItemPosition = ((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
    }

    // If the total item count is zero and the previous isn't, assume the
    // list is invalidated and should be reset back to initial state
    if (totalItemCount < previousTotalItemCount) {
        this.currentPage = this.startingPageIndex;
        this.previousTotalItemCount = totalItemCount;
        if (totalItemCount == 0) {
            this.loading = true;
        }
    }
    // If it’s still loading, we check to see if the dataset count has
    // changed, if so we conclude it has finished loading and update the current page
    // number and total item count.
    if (loading && (totalItemCount > previousTotalItemCount)) {
        loading = false;
        previousTotalItemCount = totalItemCount;
    }

    // If it isn’t currently loading, we check to see if we have breached
    // the visibleThreshold and need to reload more data.
    // If we do need to reload some more data, we execute onLoadMore to fetch the data.
    // threshold should reflect how many total columns there are too
    if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
        currentPage++;
        onLoadMore(currentPage, totalItemCount, view);
        loading = true;
    }
}

// Call this method whenever performing new searches
public void resetState() {
    this.currentPage = this.startingPageIndex;
    this.previousTotalItemCount = 0;
    this.loading = true;
}

// Defines the process for actually loading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);/ The minimum amount of items to have below your current scroll position
// before loading more.
private int visibleThreshold = 15;
// The current offset index of data you have loaded
private int currentPage = 1;
// The total number of items in the dataset after the last load
private int previousTotalItemCount = 0;
// True if we are still waiting for the last set of data to load.
private boolean loading = true;
// Sets the starting page index
private int startingPageIndex = 1;

RecyclerView.LayoutManager mLayoutManager;

public EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
}

public EndlessRecyclerViewScrollListener(GridLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
    visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
}

public EndlessRecyclerViewScrollListener(StaggeredGridLayoutManager layoutManager) {
    this.mLayoutManager = layoutManager;
    visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
}

public int getLastVisibleItem(int[] lastVisibleItemPositions) {
    int maxSize = 0;
    for (int i = 0; i < lastVisibleItemPositions.length; i++) {
        if (i == 0) {
            maxSize = lastVisibleItemPositions[i];
        }
        else if (lastVisibleItemPositions[i] > maxSize) {
            maxSize = lastVisibleItemPositions[i];
        }
    }
    return maxSize;
}

// This happens many times a second during a scroll, so be wary of the code you place here.
// We are given a few useful parameters to help us work out if we need to load some more data,
// but first we check if we are waiting for the previous load to finish.
@Override
public void onScrolled(RecyclerView view, int dx, int dy) {
    int lastVisibleItemPosition = 0;
    int totalItemCount = mLayoutManager.getItemCount();

    if (mLayoutManager instanceof StaggeredGridLayoutManager) {
        int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) mLayoutManager).findLastVisibleItemPositions(null);
        // get maximum element within the list
        lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions);
    } else if (mLayoutManager instanceof GridLayoutManager) {
        lastVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findLastVisibleItemPosition();
    } else if (mLayoutManager instanceof LinearLayoutManager) {
        lastVisibleItemPosition = ((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
    }

    // If the total item count is zero and the previous isn't, assume the
    // list is invalidated and should be reset back to initial state
    if (totalItemCount < previousTotalItemCount) {
        this.currentPage = this.startingPageIndex;
        this.previousTotalItemCount = totalItemCount;
        if (totalItemCount == 0) {
            this.loading = true;
        }
    }
    // If it’s still loading, we check to see if the dataset count has
    // changed, if so we conclude it has finished loading and update the current page
    // number and total item count.
    if (loading && (totalItemCount > previousTotalItemCount)) {
        loading = false;
        previousTotalItemCount = totalItemCount;
    }

    // If it isn’t currently loading, we check to see if we have breached
    // the visibleThreshold and need to reload more data.
    // If we do need to reload some more data, we execute onLoadMore to fetch the data.
    // threshold should reflect how many total columns there are too
    if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
        currentPage++;
        onLoadMore(currentPage, totalItemCount, view);
        loading = true;
    }
}

// Call this method whenever performing new searches
public void resetState() {
    this.currentPage = this.startingPageIndex;
    this.previousTotalItemCount = 0;
    this.loading = true;
}

// Defines the process for actually loading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);}}

MainActivity.java

  public class MainActivity extends AppCompatActivity implemens ConnectivityReceiver.ConnectivityReceiverListener {

private static final String API_KEY = "***************";
private static final String TAG = "MainActivity";
private int page = 1;
private TextView no_data_tv;
private RecyclerView mainMoviesView;
private View noInternetLayout;
private ProgressBar progressBar;
private EndlessRecyclerViewScrollListener scrollListener;
private LinearLayoutManager llm;
List<Movies> movies;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    no_data_tv = (TextView) findViewById(R.id.text_no_data);

    movies = new ArrayList<>();

    llm = new LinearLayoutManager(this);
    mainMoviesView = (RecyclerView) findViewById(R.id.main_recycler_view);
    mainMoviesView.setLayoutManager(llm);

    // This is the layout which is displayed if there is no internet connection. It is currently set to View.INVISIBLE
    noInternetLayout = findViewById(R.id.no_internet_layout);
    noInternetLayout.setVisibility(View.INVISIBLE);

    progressBar = (ProgressBar) findViewById(R.id.loading_main_activity);


    if(checkConnetion())
    {
        getDataFromServer(page);
        progressBar.setVisibility(View.INVISIBLE);
     }else
    {
        noInternetLayout.setVisibility(View.VISIBLE);
        progressBar.setVisibility(View.INVISIBLE);
    }

    scrollListener = new EndlessRecyclerViewScrollListener(llm) {
        @Override
        public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
            getDataFromServer(page);
            Log.v(TAG,"Page loaded is"+page);
        }
    };
    mainMoviesView.addOnScrollListener(scrollListener);
}

private boolean checkConnetion() {
    return ConnectivityReceiver.isConnected();
}

private void getDataFromServer(int page)
{
    // These are the retrofit codes to get the data from TMDB API
    ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);

    Call<Response> call = apiService.getPopularMovies(API_KEY , page);


    call.enqueue(new Callback<Response>() {
        @Override
        public void onResponse(Call<Response> call, retrofit2.Response<Response> response) {
            List<Movies> movies = response.body().getMovies();
            progressBar.setVisibility(View.INVISIBLE);
            if(movies.size() == 0)
            {
                no_data_tv.setVisibility(View.VISIBLE);
            }else{
               mainMoviesView.setAdapter(new MoviesAdapter(movies,MainActivity.this));
            }
        }

        @Override
        public void onFailure(Call<Response> call, Throwable t) {
            Log.e(TAG,t.toString());
        }
    });


}



@Override
protected void onResume() {
    super.onResume();
    // register connection status listener
    MyApplication.getInstance().setConnectivityListener(this);

}

@Override
public void onNetworkConnectionChanged(boolean isConnected) {
    if(isConnected)
    {
        getDataFromServer(page);

    }else{
        progressBar.setVisibility(View.INVISIBLE);
        noInternetLayout.setVisibility(View.VISIBLE);
    }
}}

我哪里出错？

Answer 1

哥们， 您每次通话时都要分配新值，
看看这一行 -

List<Movies> movies = response.body().getMovies();

您必须将元素添加到数据集中，

movies.addAll(response.body().getMovies());

Answer 2

此行始终使用新数据初始化您的视图

mainMoviesView.setAdapter(new MoviesAdapter(movies,MainActivity.this)); 

它将在onCreate（），onCreateView（）或其他初始化方法中。

MoviesAdapter moviesAdapter = new MoviesAdapter(movies,MainActivity.this); 
mainMoviesView.setAdapter(moviesAdepter);

然后你的新电话会加入队列。

call.enqueue(new Callback<Response>() {
    @Override
    public void onResponse(Call<Response> call, retrofit2.Response<Response> response) {
        movies.addAll(response.body().getMovies()); // this line updated your movies list.
        progressBar.setVisibility(View.INVISIBLE);
        if(movies.size() == 0)
        {
            no_data_tv.setVisibility(View.VISIBLE);
        }else{
            moviesAdapter.notifyDataSetChanged(); // this new line.
        }
    }

    @Override
    public void onFailure(Call<Response> call, Throwable t) {
        Log.e(TAG,t.toString());
    }
});