Question

我正在尝试从数据库中检索JSONObject，但我发现该请求甚至没有进入服务器。我检查了Apache Access Log以确认这一点。 URL有效，当我通过Web浏览器访问它时，它返回expect JSONObject。 Volley库显示异常错误null。

 private void GetSchInfo(){

    showDialog();

    // making fresh volley request and getting json
    JsonObjectRequest jsonReq = new JsonObjectRequest(Request.Method.GET,
            URL_SchInfo, null, new Response.Listener<JSONObject>() {

        @Override
        public void onResponse(JSONObject response) {


            try{

                spinnerClass.setVisibility(View.VISIBLE);
                spinnerSch.setVisibility(View.VISIBLE);
                spinnerDept.setVisibility(View.VISIBLE);
                btnRegClass.setVisibility(View.VISIBLE);
                txtClassMsg.setVisibility(View.VISIBLE);
                btnRefresh.setVisibility(View.GONE);

                JSONArray schools = response.getJSONArray("sch_info");
                JSONArray departments = response.getJSONArray("dept_info");

                for (int i = 0; i < schools.length(); i++){
                    JSONObject schObj = (JSONObject)schools.get(i);
                    SchInfo sch = new SchInfo(schObj.getString("school_id"), schObj.getString("school_name"));
                    schoolList.add(sch);
                }

                for (int j = 0; j < departments.length(); j++){
                    JSONObject deptObj = (JSONObject)departments.get(j);
                    DeptItem dept = new DeptItem(deptObj.getString("department_id"), deptObj.getString("department_name"));
                    deptList.add(dept);
                }


                //populate
                //populateInfo();

            }catch(JSONException e){
               Log.e(TAG, "JSON Error: " + e.getMessage());
                e.printStackTrace();
                spinnerClass.setVisibility(View.GONE);
                txtClassMsg.setVisibility(View.GONE);
                spinnerSch.setVisibility(View.GONE);
                spinnerDept.setVisibility(View.GONE);
                btnRegClass.setVisibility(View.GONE);
                btnRefresh.setVisibility(View.VISIBLE);

             }

            hideDialog();
        }
    }, new Response.ErrorListener() {

        @Override
        public void onErrorResponse(VolleyError error) {
            String body;

                if (error.networkResponse.data !=null){
                try {
                    body = new String(error.networkResponse.data, "UTF-8");
                }catch (UnsupportedEncodingException e){
                    e.printStackTrace();
                }
            }

          Log.e("Error: ",   error.getCause()  +">>" + error.getMessage());
            Log.e(TAG, "JSON Error: " + error.getMessage() );
            hideDialog();
            spinnerClass.setVisibility(View.GONE);
            spinnerSch.setVisibility(View.GONE);
            spinnerDept.setVisibility(View.GONE);
            btnRegClass.setVisibility(View.GONE);
            txtClassMsg.setVisibility(View.GONE);
            btnRefresh.setVisibility(View.VISIBLE);
        }
    });

    // Adding request to volley request queue
    AppController.getInstance().addToRequestQueue(jsonReq);
}

我该如何解决这个问题？

注意服务器在我的本地计算机上，我通过热点连接http://192.164.***.***。

Answer 1

尝试从Android移动设备的浏览器做一个请求，如果它完全正常，那么必须是凌空问题。如果它不起作用那么这意味着你只能输入192.168就无法连接到服务器.... 还要检查此链接并在模拟器中运行应用程序： How to connect to my http://localhost web server from Android Emulator in Eclipse

所以，无论如何你想使用这样的服务器使你的服务器上线。并使用您的全局IP来ping服务器。阅读如何根据您自己的服务器文档将本地服务器联机。

Answer 2

我的策略是，制作Volley单身并从任何地方使用它。这是步骤：在build.gradle文件中添加此gradle

compile 'com.mcxiaoke.volley:library-aar:1.0.0'

像这样创建应用程序类

public class YourApplication extends Application {

    public static final String TAG = YourApplication.class.getSimpleName();
    private RequestQueue requestQueue;
    private com.android.volley.toolbox.ImageLoader imageLoader;
    private static YourApplication instace;

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

    public static synchronized YourApplication getInstance() {
        return instace;
    }

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

        return requestQueue;
    }

    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 (requestQueue != null) {
            requestQueue.cancelAll(tag);
        }
    }
}

在menifest.xml

中添加以下代码

<application
        android:name=".package_path.YourApplication">

在清单中添加互联网权限

<uses-permission android:name="android.permission.INTERNET" />

现在你的截击配置了。你只需这样使用它：

final ProgressDialog progressDialog = new ProgressDialog(this, ProgressDialog.THEME_HOLO_LIGHT);
        progressDialog.setMessage("Please wait...");
        progressDialog.setCancelable(false);
        progressDialog.show();

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

                    @Override
                    public void onResponse(JSONObject object) {
                        progressDialog.dismiss();
            // Your Data is here
                }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                progressDialog.dismiss();
        //Error Occured


            }
        });
        jsonObjectRequest.setRetryPolicy(new DefaultRetryPolicy(30000, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        YourApplication.getInstance().addToRequestQueue(jsonObjectRequest, "YOUR_TAG");

修改在build.gradle文件中使用compile 'com.android.volley:volley:1.0.0''。

compile 'com.mcxiaoke.volley:library-aar:1.0.0' is just deprecated.

就是这样:)）

Answer 3

getMessage（）有时不起作用。尝试此代码以获取服务器返回的完整错误消息。

    if (volleyError != null && volleyError.networkResponse != null) {
        int statusCode = volleyError.networkResponse.statusCode;
        Log.w(tagToUse, TAG + " response code:" + statusCode + "");
        byte[] data = volleyError.networkResponse.data;
        int length = data.length;
        StringBuilder stringBuilder = new StringBuilder(length);
        for (int x = 0; x < length; x++) {
            stringBuilder.append(((char) data[x]));
        }
        String errorMessage = stringBuilder.toString();
        Log.d(tagToUse, TAG + " Server error data: " + errorMessage);
    }

Answer 4

这可能是由于URL不安全所致，因此您可以在AndroidManifest.xml中添加此行

android：usesCleartextTraffic =“ true”

 <application
    android:name=".ExampleApp"
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher_new"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_circle"
    android:largeHeap="true"
    android:resizeableActivity="false"
    android:usesCleartextTraffic="true"
    android:screenOrientation="portrait"
    android:theme="@style/AppTheme.NoActionBar">

，如果出现此错误[java.lang.NoClassDefFoundError：失败的解决方案：Lorg / apache / http / ProtocolVersion]错误，则将该行添加为应用程序标记子项。

<uses-library android:name="org.apache.http.legacy" android:required="false"/>

有关更多详细信息，请访问此链接-

https://developer.android.com/about/versions/pie/android-9.0-changes-28#apache-p

Answer 5

兄弟首先检查API（应用程序编程接口），您的响应是否在 Json 中，然后下一步是使用 volley。我认为你的 API 不正确

Volley库不会连接到Server

5 个答案: