在Android中通过JSON填充微调器

Question

我有这样的JSON数据：

[{"id":"1",
"client_name":"Glasco Smith Klin",
"campaign_name":"Health Medicine Survay",
"question":"MODE OF COMPLAINT CAN BE GIVEN THROUGH __________________",
"option_A":"WRITTEN",
"option_B":"ORAL",
"option_C":"PHONE CALL",
"option_D":"ALL OF THE ABOVE",
"q_prefix":"GSKHMSQ"},

{"id":"2",
"client_name":"Glasco Smith Klin",
"campaign_name":"Health Medicine Survay",
"question":"ADDING NEW FIR CAN BE DONE FROM WHICH ROLE",
"option_A":"IO",
"option_B":"TRAFFIC",
"option_C":"SHO-CRIME",
"option_D":"ADMINISTRATOR",
"q_prefix":"GSKHMJD"}]

我想将所有q_prefix列检索到微调器中。 但是在我的微调器中没有显示任何数据。 当我运行我的应用程序，我得到一个错误：“无法启动活动”，并Java.lang.NullPointerException在这一行： jsonArray = jSon.getJSONArray(TAG_CODE); 。

这是我的代码：

public class SpinDemo extends Activity {

    private static String strUrl = "http://192.168.1.61/jyoti/android_app/all_questions.php";
    private static String TAG_ID = "id";
    private static String TAG_CODE = "q_prefix";
    JSONArray jsonArray = null;
    Spinner codeSpinner, spinner2;

    @SuppressWarnings("unused")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        codeSpinner = (Spinner) findViewById(R.id.spinner2);

        ArrayList<String> codeList = new ArrayList<String>();

        // creating instance of JSONPrser
        JSONParser jParser = new JSONParser();
        // getting JSON string from URL
        JSONObject jSon = jParser.getJSONFromUrl(strUrl);
        System.out.println("Hello ********************");

        try {
            // Getting Array of Code
            jsonArray = jSon.getJSONArray(TAG_CODE);
            final String[] items = new String[jsonArray.length()];
            // looping through All Contacts
            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject c = jsonArray.getJSONObject(i);

                // Storing each json item in variable
                String strCode = c.getString(TAG_CODE);
                items[i] = c.getString(TAG_CODE);
                System.out.println("Hello events " + items);
            }

            ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                    android.R.layout.simple_spinner_item);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            codeSpinner.setAdapter(adapter);
        } catch (JSONException je) {
            je.printStackTrace();

        }

    }

}

Answer 1

您可以在Android App中检查以下代码以使用Spinner解析json数据：

public class ParseJsonAndroidExample extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_parse_json_android_example);


    final Spinner output = (Spinner) findViewById(R.id.output);
    final Button bparsejson      = (Button) findViewById(R.id.bparsejson);
    String OutputData ;
    ArrayList<String> outputDataList  = new ArrayList<String>();


    /************  Static JSON data ***********/
    final String strJson = "{ "Android" :[{"id":"1",
                                      "client_name":"Glasco Smith Klin",
                                      "campaign_name":"Health Medicine Survay",
                                      "question":"MODE OF COMPLAINT CAN BE GIVEN THROUGH __________________",
                                        "option_A":"WRITTEN",
                                         "option_B":"ORAL",
                                       "option_C":"PHONE CALL",
                                        "option_D":"ALL OF THE ABOVE",
                                        "q_prefix":"GSKHMSQ"},

                                         {"id":"2",
                                          "client_name":"Glasco Smith Klin",
                                           "campaign_name":"Health Medicine Survay",
                                           "question":"ADDING NEW FIR CAN BE DONE FROM WHICH ROLE",
                                            "option_A":"IO",
                                             "option_B":"TRAFFIC",
                                             "option_C":"SHO-CRIME",
                                             "option_D":"ADMINISTRATOR",
                                              "q_prefix":"GSKHMJD"}] }";


    /******** Listener for button click ********/
    bparsejson.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {

           String OutputData = "";
           JSONObject jsonResponse;

           try {

                /****** Creates a new JSONObject with name/value mappings from the JSON string. ********/
                jsonResponse = new JSONObject(strJson);

                /***** Returns the value mapped by name if it exists and is a JSONArray. ***/
                /*******  Returns null otherwise.  *******/
                JSONArray jsonMainNode = jsonResponse.optJSONArray("Android");

                /*********** Process each JSON Node ************/

                int lengthJsonArr = jsonMainNode.length();  

                for(int i=0; i < lengthJsonArr; i++) 
                {
                    /****** Get Object for each JSON node.***********/
                    JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);

                    /******* Fetch node values **********/
                    int id        = Integer.parseInt(jsonChildNode.optString("id").toString());
                    String client_name   = jsonChildNode.optString("client_name").toString();
                    String campaign_name=    jsonChildNode.optString("campaign_name").toString();
                   String question= jsonChildNode.optString("question").toString();
                   String option_A= jsonChildNode.optString("option_A").toString();

String option_B= jsonChildNode.optString("option_B").toString();
String option_C= jsonChildNode.optString("option_C").toString();
 String option_D= jsonChildNode.optString("option_D").toString(); 
String q_prefix= jsonChildNode.optString("q_prefix").toString();


                    OutputData += "Node : \n\n     "+ id +" | "
                                                        + client_name+" | "
                                                        + campaign_name+" 
                                                         + question+" | "
                                                         + option_A+" | "
                                                         + option_B+" | "
                                                         + option_C+" | "
                                                          + option_D+" | "
                                                          + q_prefix+" | " +"\n\n ";




               }
              outputDataList.add(OutputData);


                /************ Show Output on Spinner **********/

       ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_spinner_item ,outputDataList  );
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    codeSpinner.setAdapter(adapter);



            } catch (JSONException e) {

                e.printStackTrace();
            }

        }
    });
 }
}

Answer 2

尝试这样，使用AsyncTask进行网络操作

“无法启动活动”和Java.lang.NullPointerException在j的线sonArray = jSon.getJSONArray(TAG_CODE);

首先使用此代码进行解析

jsonArray = new JSONArray(jSon.toString());
        final String[] items = new String[jsonArray.length()];
        // looping through All Contacts
        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject c = jsonArray.getJSONObject(i);

            // Storing each json item in variable
            String strCode = c.getString(TAG_CODE);
            items[i] = c.getString(TAG_CODE);
            System.out.println("Hello events " + items);
        }

然后使用项目到ArrayAdapter

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                    android.R.layout.simple_spinner_item,items);

Answer 3

 JSONObject jSon = jParser.getJSONFromUrl(strUrl);
your response is JsonArray not  JsonObject
if Response starts with [ it is an jsonarray
if starts with { it is an jsonObject.

采用

  public static int SDK_INT = android.os.Build.VERSION.SDK_INT;

 if (SDK_INT >= 10) {
        ThreadPolicy tp = ThreadPolicy.LAX;
        StrictMode.setThreadPolicy(tp);
        }

解析Json之前

否则使用AsyncTask获得响应

http://developer.android.com/reference/android/os/AsyncTask.html

Answer 4

您没有将items Array传递给ArrayAdapter构造函数，方法是：

 ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                    android.R.layout.simple_spinner_item,items);

而不是从主线程发出Web服务请求，而是使用AsyncTask在后台执行操作，并在操作完成后更新UI元素

Answer 5

问题与解决方案：

1. 检查您的logcat，它应该具有NetworkOnMainThreadException ，原因是您是直接在主线程上调用Web API，从Honeycomb开始，不可能直接在Main UI Thread上实现长时间运行的任务。

   解决方案是实现线程机制，您可以在android中实现AsyncTask ，这在Android中称为无痛线程 。

2. JSON解析中存在问题，您需要正确学习和理解JSON解析 。

问题示例：

 JSONObject jSon = jParser.getJSONFromUrl(strUrl);
        System.out.println("Hello ********************");

        try {
            // Getting Array of Code
            jsonArray = jSon.getJSONArray(TAG_CODE);

             .....
             .....

通过查看有问题的响应，我可以说您是直接在响应中获取JSONArray而不是JSONObject。

JSON解析中的第二个错误是您尝试获取不是必需的JSONArray（TAG_CODE），因为您已经有JSONArray作为响应，您可以遍历对象并获取所需的任何值。