如何使用 Volley 进行并发 GET 调用？

Question

我有 3 个 API GET 调用。我的方法面临的问题是，该应用程序能够从两个 API 成功获取数据，并且我也能够在 UI 上显示它。但是，对于第三次 API 调用，由于以下错误，之前显示的数据消失了，这很糟糕。

D/Volley: [380] BasicNetwork.logSlowRequests: HTTP response for request=<[ ] http://example.com/api/search/getTwitterData?limit=10&tag=JavaScript 0x865f5dc2 NORMAL 3> [lifetime=6683], [size=10543], [rc=200], [retryCount=0]

如何使用 Volley 进行并发 API GET 调用而不丢失 UI 上的数据。有人可以指导我吗？

以下是我的代码的摘录。

public class StaggeredSearchActivity extends AppCompatActivity {

    ...

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

        requestQueue = Volley.newRequestQueue(this);

        Intent intent = getIntent();
        String searchText = intent.getStringExtra("searchText");

        // Three concurrent API GET Calls  
        getMediumData(searchText);
        getExampleData(searchText);
        getGoogleData(searchText);

        recyclerView = findViewById(R.id.staggered_recycler_view);
        staggeredGridLayoutManager = new StaggeredGridLayoutManager(2, LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(staggeredGridLayoutManager);
    }

    ArrayList<StaggeredCustomCard> dataset = new ArrayList<>();

    private void getMediumData(String searchText) {
        progressBar = findViewById(R.id.progressBar);
        progressBar.setVisibility(View.VISIBLE);

        String url = UrlConstants.getUrl() + searchText;

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            progressBar.setVisibility(View.INVISIBLE);
                            JSONArray array = response.getJSONArray("mediumposts");

                            ...

                            dataset.add(new StaggeredCustomCard(user, userpost, postdate));
                            }
                            staggeredGridAdapter = new StaggeredGridAdapter(StaggeredSearchActivity.this, dataset);
                            recyclerView.setAdapter(staggeredGridAdapter);
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }

                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // TODO: Handle error
                        progressBar.setVisibility(View.INVISIBLE);
                    }
                });

        jsonObjectRequest.setRetryPolicy(new DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonObjectRequest);
    }

    private void getExampleData(String searchText) {

        ...

        JsonArrayRequest jsonArrayRequest = new JsonArrayRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONArray>() {

                    @Override
                    public void onResponse(JSONArray response) {
                        try {
                            ...
                            dataset.add(new StaggeredCustomCard(user, userpost, postdate));
                                staggeredGridAdapter = new StaggeredGridAdapter(StaggeredSearchActivity.this, dataset);
                                recyclerView.setAdapter(staggeredGridAdapter);
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        ...
                    }
                });

        jsonArrayRequest.setRetryPolicy(new DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonArrayRequest);
    }

    private void getGoogleData(String searchText) {
        ...

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {
                        ...

                        dataset.add(new StaggeredCustomCard(user, userpost, postdate));

                            }
                            staggeredGridAdapter = new StaggeredGridAdapter(StaggeredSearchActivity.this, dataset);
                            recyclerView.setAdapter(staggeredGridAdapter);
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }

                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        ...
                    }
                });

        jsonObjectRequest.setRetryPolicy(new DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonObjectRequest);
    }
}

Answer 1

这种方法没有多大意义。一旦你从三个端点之一得到响应，你似乎创建了一个新的适配器并将它附加到回收器，每次随机 "notifyDataSetChanged"...

也许可以考虑将 ViewModel 与处理业务登录的服务层和网络层一起使用。
ViewModel updates/posts MutableLiveData> 当网络方法之一的回调从端点响应时...合并三块数据。
activity 只是观察 ViewModel 的 MutableLiveData 并使用 DiffUtil 更新回收器中的 look/cards。

Answer 2

问题是您每次都在初始化适配器，这就是为什么您的数据在新的 API 调用后会丢失的原因。我更喜欢下面的方法，这样可以帮助你，在 ArrayList 中添加数据并通知适配器，

在onCreate中添加这一行，

staggeredGridAdapter = new StaggeredGridAdapter(StaggeredSearchActivity.this, dataset);
recyclerView.setAdapter(staggeredGridAdapter);

API 回调响应的变化：

                             ...

dataset.add(new StaggeredCustomCard(user, userpost, postdate));

循环后添加下面一行

staggeredGridAdapter.notifyDataSetChanged();

适配器的变化

 private ArrayList<StaggeredCustomCard> dataSet;
        private Context context;

        public MyAdapter(ArrayList<StaggeredCustomCard> dataSet, Context context) {
            this.data = data;
            this.context = context;
        }

注意：不要在适配器上创建新对象。

Answer 3

数据不应因该错误而消失。首先，我建议您检查是否清除了某个地方的数据集，或者您的屏幕是否正在重新创建。

其次，我建议您从 Volley 转移，因为它与需要大量关注细节的现代技术库相比已经过时了。使用 Retrofit - 它是现代的、强大的和社区认可的库。使用它，您将确保您想要异步的所有请求都是异步的，并且所有响应都得到了很好的处理。

此外，我建议您不要在每次加载数据时都创建适配器，而是使用一个适配器并向其添加数据，然后它们使用 notifyDataSetChanged() 重新加载包含相关数据的列表。

Answer 4

最好的方法是在 onCreate 方法的 StaggeredSearchActivity 中注册您的 LiveData 并像您一样监听数据库更改。在每个成功响应中，将其结果保存到没有 LiveData 的数据库中。 onCreate方法中的LiveData会被触发

   @Override


  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

  ViewModel viewModel = ViewModelProviders.of(this, factory).get(ViewModel.class);
            viewModel.getEntity().observe(this, entity -> {
                if (entity != null) {
                    adapter.notifyDataSetChanged(entity );

                }
            });

    requestQueue = Volley.newRequestQueue(this);

    Intent intent = getIntent();
    String searchText = intent.getStringExtra("searchText");

    // Three concurrent API GET Calls
    getMediumData(searchText);
    getExampleData(searchText);
    getGoogleData(searchText);

    recyclerView = findViewById(R.id.staggered_recycler_view);
    staggeredGridLayoutManager = new StaggeredGridLayoutManager(2, LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(staggeredGridLayoutManager);
}

ArrayList<StaggeredCustomCard> dataset = new ArrayList<>();

private void getMediumData(String searchText) {
    progressBar = findViewById(R.id.progressBar);
    progressBar.setVisibility(View.VISIBLE);

    String url = UrlConstants.getUrl() + searchText;

    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
            (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {



                   @Override
                    public void onResponse(JSONObject response) {
                        StaggeredCustomCardDAO.insert();
                        // TODO just insert to dataBase
                    }

                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // TODO: Handle error
                        progressBar.setVisibility(View.INVISIBLE);
                    }
                });

        jsonObjectRequest.setRetryPolicy(new

                DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonObjectRequest);
    }

    private void getExampleData(String searchText) {


        JsonArrayRequest jsonArrayRequest = new JsonArrayRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONArray>() {

                    @Override
                    public void onResponse(JSONArray response) {
                        try {

                            // TODO just insert to dataBase
                          StaggeredCustomCardDAO.insert();
                        } catch (
                                JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
                });

        jsonArrayRequest.setRetryPolicy(new DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonArrayRequest);
    }

    private void getGoogleData(String searchText) {


        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
                (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {

                        // TODO just insert to dataBase
StaggeredCustomCardDAO.insert();
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
                });

        jsonObjectRequest.setRetryPolicy(new DefaultRetryPolicy(
                DefaultRetryPolicy.DEFAULT_TIMEOUT_MS * 15,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(jsonObjectRequest);


    }


    class ViewModel extends androidx.lifecycle.ViewModel {


        private LiveData<StaggeredCustomCard> entity;


        public ViewModel(Repository repository) {
            entity = repository.getNetworkData();
        }


        public LiveData<StaggeredCustomCard> getEntity() {
            return entity;
        }
    }

    class Repository {

        LiveData<StaggeredCustomCard> getNetworkData() {

            LiveData<StaggeredCustomCard> localeData =  StaggeredCustomCardDAO .getLocaleData();//... todo Read from data base
            return localeData;
        }
    @Dao
    public interface StaggeredCustomCardDAO {
        @Query("Select * from tbl_staggeredCustomCard ")
        LiveData<StaggeredCustomCard> getLocaleData();

        @Insert(onConflict = OnConflictStrategy.REPLACE)
        void insert(List<StaggeredCustomCard> items);

    }
    }

Answer 5

第一种方式：首先我建议你建立一个中央请求队列。

public class AppController extends Application {
    public static final String TAG = AppController.class
            .getSimpleName();
    private RequestQueue mRequestQueue;

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized AppController getInstance() {
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        // set the default tag if tag is empty
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }
}

然后将您想要的请求添加到队列中

// Adding request to request queue
AppController.getInstance().addToRequestQueue(jsonObjReq);

第二种方式：创建一个 Generic Volley class 和一个接口，使用接口获取成功和失败响应。

第 1 步创建一个单独的 Volley class 第 2 步创建用于访问来自 volley class 的响应的接口第 3 步为 class 创建新对象并发送所需参数新的 PostVolleyJsonRequest(TestVolley.this, TestVolley.this(interfcae), "Submit", url, 参数);

class 的上下文发送成功失败响应的接口成功时识别的请求类型 url（必填项）参数（可选） GET 不需要通用截击 class

public class PostVolleyJsonRequest {
private String  type;
private Activity act;
private VolleyJsonRespondsListener volleyJsonRespondsListener;
private String networkurl;
private JSONObject jsonObject = null;
private JSONObject params;


public PostVolleyJsonRequest(Activity act, VolleyJsonRespondsListener volleyJsonRespondsListener, String type, String netnetworkUrl,JSONObject params) {
    this.act = act;
    this.volleyJsonRespondsListener = volleyJsonRespondsListener;
    this.type = type;
    this.networkurl = netnetworkUrl;
    this.params = params;
    sendRequest();
}

private void sendRequest() {

    Log.d("url", "url" + networkurl);
    JsonObjectRequest jsObjRequest = new JsonObjectRequest(Request.Method.POST,networkurl,params,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    Log.e("response", "response " + response);
                    volleyJsonRespondsListener.onSuccessJson(response, type);
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    try {
                        NetworkResponse response = error.networkResponse;
                        Log.e("response", "response " + response);
                        if (response != null) {
                            int code = response.statusCode;

                            String errorMsg = new String(response.data);
                            Log.e("response", "response" + errorMsg);
                            try {
                                jsonObject = new JSONObject(errorMsg);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                            String msg = jsonObject.optString("message");
                            volleyJsonRespondsListener.onFailureJson(code, msg);
                        } else {
                            String errorMsg = error.getMessage();
                            volleyJsonRespondsListener.onFailureJson(0, errorMsg);
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });

    jsObjRequest.setRetryPolicy(new DefaultRetryPolicy(
            600000,
            DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
            DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

    RequestQueue requestqueue = Volley.newRequestQueue(act);
    requestqueue.add(jsObjRequest);

}
}

Use the interface to get responds message

public interface VolleyJsonRespondsListener {

public void onSuccessJson(JSONObject result, String type);
public void onFailureJson(int responseCode, String responseMessage);
}

在您要包含多个请求的class中

public class TestVolley extends AppCompatActivity implements VolleyJsonRespondsListener{

//Your class code goes here


//network request

try {
        //parameters 
        //Context,Interface,Type(to indentify your responds),URL,parameter for your request 

        //request 1
        new PostVolleyJsonRequest(TestVolley.this, TestVolley.this, "Submit", url, params);

        //request 2
        new PostVolleyJsonRequest(TestVolley.this, TestVolley.this, "AccessData", url_2, params_2);




 } catch (Exception e) {

 e.printStackTrace()
 }

 //Methods from Interface

  @Override
public void onSuccessJson(JSONObject result, String type) {

   //Based on the Type you send get the responds and parse it 
    switch (type) {
        case "Submit":
            try {
                parseSubmit(result);
            } catch (Exception e) {

如何使用 Volley 进行并发 GET 调用？

How to make concurrent GET calls using Volley?

java

android

asynchronous

android-volley