Android:如何在recyclerView的后台加载更多数据 [英] Android: How can I load more data in the background in recyclerView

问题描述

我正在创建一个新的android应用程序，我几乎已经完成了第一个屏幕.但是，只要我到达屏幕底部，应用程序就会立即将我带到页面的开头，而不是加载新数据.

I am creating a new android app, I have nearly completed the first screen. However, as soon as I reach the bottom of the screen, instead of loading new data, the app throws me right to the beginning of the page.

当我发送第二页的请求时，我正在使用的API将发送下一页.您能告诉我如何制作该应用程序，以便它在用户到达第一页末尾之前自动发送对第二页的请求.

The API that I'm using will send the next page when I send a request for the second page. Can you please tell me how can I make the app such that, it automatically sends the request for the second page, before the user reaches the end of the first page.

我正在使用volley库以及recyclerView和cardView.您能否清楚说明我应该在哪里进行更改，我是应用程序开发的新手.

I'm using volley library along with recyclerView and cardView. Can you please explain clearly as to where am I supposed to make changes, I am new to app development.

以下是排球要求:

private void discoverMovies() {

    final ProgressDialog progressDialog = new ProgressDialog(getContext());
    progressDialog.setMessage("Fetching Data From DB");
    progressDialog.show();

    //Requesting the data.....
    StringRequest stringRequest = new StringRequest(Request.Method.GET, tempURL,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    try {
                        progressDialog.dismiss();
                        JSONObject parentObject = new JSONObject(response);
                        JSONArray parentArray = parentObject.getJSONArray("results");

                        for (int i = 0; i < parentArray.length(); i++) {
                            JSONObject object = parentArray.getJSONObject(i);
                            movieModel model = new movieModel(
                                    object.getString("title"),
                                    object.getString("overview"),
                                    object.getString("release_date"),
                                    object.getString("poster_path"),
                                    object.getInt("id"),
                                    object.getBoolean("adult"),
                                    object.getInt("vote_count"),
                                    object.getDouble("vote_average"),
                                    object.getString("original_language"),
                                    object.getString("backdrop_path")
                            );

                            movieModels.add(model);
                            adapter = new cardViewAdapter(getContext(), movieModels);
                            recyclerView.setAdapter(adapter);
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    progressDialog.dismiss();
                    Toast.makeText(getActivity(), error.getLocalizedMessage(), Toast.LENGTH_LONG).show();
                }
            });

    RequestQueue requestQueue = Volley.newRequestQueue(getContext());
    requestQueue.add(stringRequest);
}

推荐答案

引用

Refer this. Its explained in a cool fashion here.

基本上，您需要一个onScrollChangeListener来检测recyclerview中的滚动变化，但是仅此一项是无济于事的.因此，您需要一种方法来检查您当前是否到达了recyclerview的底部.所以这是您的操作方式:

Basically you need an onScrollChangeListener to detect scroll changes in your recyclerview but that alone wont help. So you need a way to check whether you are currently reaching the bottom of your recyclerview. so here's how you do it:

在上面的链接中选中此行

Check this line in the above link

// 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.
        if (!loading && (firstVisibleItem + visibleItemCount + visibleThreshold) >= totalItemCount ) {
            loading = onLoadMore(currentPage + 1, totalItemCount);
        }

查看变量 visibleThreshold ，您可以在其中修改并应用自己的自定义值来进行第二次调用.

See the variable visibleThreshold that is where you modify and apply you own custom value to make the second call.

让我们使用以下值进行检查:

lets check that with values:

如果visibleThreshold为0，并且列表中有10个项目，而您位于第6个项目上，则第一个项目是第0个项目: 这条线

if visibleThreshold is 0 and you have 10 items in your list and you`re on the 6 item and the first item is the 0th item: the this line

if (!loading && (firstVisibleItem + visibleItemCount + visibleThreshold) >= totalItemCount )

解释为-> if(true&&(0 + 6 + 0)> = 10)解释为false！

interprets as -> if (true && (0+6+0)>=10) which interprets as false!

因此，第二个呼叫现在不会发出.当您的lastitem是第十个项目(因为您的阈值为0)时，它将完成

thus the second call wont be made now. it will be made when you lastitem is the 10th item (as your threshold is 0)

但是现在，如果您将阈值添加为4，则在满足条件的情况下进行下一个调用: 解释为-> if(true&&(0 + 6 + 4)> = 10)解释为true！

But now if you add a threshold of 4, the next call is made as the condition now is satisfied: interprets as -> if (true && (0+6+4)>=10) which interprets as true!

总结一下，visibleThreshold是您添加逻辑的地方，您可以通过链接实现样板代码！

Summarizing, the visibleThreshold is where you add your logic, rest you can implement the boiler plate code from the link!

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