将数组传递给doInBackground函数并从中获取结果？

我想传递一个数组到doInbackground（）函数并从中获取结果。实际上我不知道如何将数组传递给PhP文件以及如何在数据库中进行搜索。请如果你不想帮助不要让它重复或让别人不帮我。这里是我试过的代码。将数组传递给doInBackground函数并从中获取结果？

首先，我从服务器数据库获取值并解析它，并希望将其存储在数组中。整个图象CODE

public class eventsFragment extends Fragment { 
ImageView imageView; 
ListView listEvents; 
private TextView noevents; 
SessionManager session; 
String JSONString, json_string; 
ArrayList<String> json_string1; 

JSONObject jsonObject; 
AdapterOwnEvents adapterOwnEvents; 
JSONArray jsonArray; 


public eventsFragment() { 
    // Required empty public constructor 
} 


@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    // Inflate the layout for this fragment 
    View view = inflater.inflate(R.layout.fragment_news_feed, container, false); 
    listEvents = (ListView) view.findViewById(R.id.listEvents1); 
    noevents = (TextView) view.findViewById(R.id.noEvents); 
    return view; 
} 

@Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 

    SearchFriends(); 
} 

public void SearchFriends() { 
    session = new SessionManager(getActivity().getApplicationContext()); 
    HashMap<String, String> user = session.getUserDetails(); 
    String user_id = user.get(SessionManager.KEY_ID); 
    new BackgroundSearch().execute(user_id); 

} 

class BackgroundSearch extends AsyncTask<String, Void, String> { 
    String search_url; 

    @Override 
    protected void onPreExecute() { 
     search_url = "http://www.example.com/friendList.php"; 
    } 

    @Override 
    protected String doInBackground(String... params) { 
     String user_id = params[0]; 

     try { 
      URL url = new URL(search_url); 
      HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); 
      httpURLConnection.setRequestMethod("POST"); 
      httpURLConnection.setDoOutput(true); 
      OutputStream outputStream = httpURLConnection.getOutputStream(); 
      BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8")); 
      String data = URLEncoder.encode("user_id", "UTF-8") + "=" + URLEncoder.encode(user_id, "UTF-8"); 
      bufferedWriter.write(data); 
      bufferedWriter.flush(); 
      bufferedWriter.close(); 
      outputStream.close(); 
      InputStream inputStream = httpURLConnection.getInputStream(); 
      BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream)); 
      StringBuilder stringBuilder = new StringBuilder(); 
      while ((JSONString = bufferedReader.readLine()) != null) { 

       stringBuilder.append(JSONString).append("\n"); 
      } 
      bufferedReader.close(); 
      inputStream.close(); 
      httpURLConnection.disconnect(); 
      return stringBuilder.toString().trim(); 

     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
     return null; 
    } 

    @Override 
    protected void onProgressUpdate(Void... values) { 
     super.onProgressUpdate(values); 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     json_string = result; 
     try { 
      jsonObject = new JSONObject(json_string); 
      jsonArray = jsonObject.getJSONArray("server_response"); 

      int count = 0; 
      String friend_id; 
      ArrayList<String> array1 = new ArrayList<String>(); 
      while (count < jsonArray.length()) { 
       JSONObject JO = jsonArray.getJSONObject(count); 
       friend_id = JO.getString("friend_id"); 
       array1.add(friend_id); 

       count++; 
      } 
      new BackgroundSearchEvents().execute(array1); 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 

    } 
} 

class BackgroundSearchEvents extends AsyncTask<ArrayList<String>, Void, String> { 
    String search_url; 

    @Override 
    protected void onPreExecute() { 
     search_url = "http://www.example.com/eventList.php"; 
    } 


    @SafeVarargs 
    @Override 
    protected final String doInBackground(ArrayList<String>... passing) { 
     // ArrayList<String> result = new ArrayList<String>(); 
     ArrayList<String> passed = passing[0]; 


     try { 
      URL url = new URL(search_url); 
      HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); 
      httpURLConnection.setRequestMethod("POST"); 
      httpURLConnection.setDoOutput(true); 
      OutputStream outputStream = httpURLConnection.getOutputStream(); 
      BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8")); 
      // int count = 0; 
      String user_id; 
      for (int count = 0 ; count<passing.length; count++) { 
       user_id=passed.get(count); 
       String data = URLEncoder.encode("user_id", "UTF-8") + "=" + URLEncoder.encode(String.valueOf(user_id), "UTF-8"); 
       bufferedWriter.write(data); 
       bufferedWriter.flush(); 
       bufferedWriter.close(); 
       outputStream.close(); 
       InputStream inputStream = httpURLConnection.getInputStream(); 
       BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream)); 
       StringBuilder stringBuilder = new StringBuilder(); 
       while ((JSONString = bufferedReader.readLine()) != null) { 

        stringBuilder.append(JSONString).append("\n"); 
       } 
       bufferedReader.close(); 
       inputStream.close(); 
       httpURLConnection.disconnect(); 
       return stringBuilder.toString().trim(); 
       // count++; 



      } 
     // return result; 
      //return stringBuilder.toString().trim(); 


     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
     return null; 
    } 

    @Override 
    protected void onProgressUpdate(Void... values) { 
     super.onProgressUpdate(values); 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     json_string = result; 
     ParseJson(); 
    } 
} 

public void ParseJson() { 

    if (json_string == null) { 
     Toast.makeText(getActivity(), "No Events", Toast.LENGTH_LONG).show(); 
    } else { 
     // listEvents.setAdapter(adapterOwnEvents); 
     adapterOwnEvents = new AdapterOwnEvents(getActivity(), R.layout.own_event_list); 
     listEvents.setAdapter(adapterOwnEvents); 
     try { 
      jsonObject = new JSONObject(json_string); 
      jsonArray = jsonObject.getJSONArray("server_response"); 

      int count = 0; 
      String event_id, event, event_type, date, image, friend_id; 
      while (count < jsonArray.length()) { 
       JSONObject JO = jsonArray.getJSONObject(count); 
       event_id = JO.getString("event_id"); 
       event = JO.getString("event"); 
       date = JO.getString("date"); 
       event_type = JO.getString("event_type"); 
       friend_id = JO.getString("user_id"); 
       image = ("http://example.com/uploads/" + friend_id + ".png"); 

       Own_EventListElements own_eventListElements = new Own_EventListElements(event_id, event, event_type, date, image); 
       adapterOwnEvents.add(own_eventListElements); 
       listEvents.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
        public void onItemClick(AdapterView<?> parent, View view, 
              int position, long id) { 

         Own_EventListElements eventsElements = (Own_EventListElements) adapterOwnEvents.getItem(position); 
         Intent i = new Intent(getActivity(), SendGreetings.class); 

         startActivity(i); 
        } 
       }); 
       count++; 
      } 


     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 
    } 
} 


}

这是我的适配器

public class AdapterOwnEvents extends ArrayAdapter { 
List list=new ArrayList(); 
public AdapterOwnEvents(Context context, int resource) { 
    super(context, resource); 
} 
public void add(Own_EventListElements object) { 
    super.add(object); 
    list.add(object); 
} 
@Override 
public int getCount() { 
    return list.size(); 
} 

@Override 
public Object getItem(int position) { 
    return list.get(position); 
} 
@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    View view; 
    view=convertView; 
    ElementsHolder elemetsHolder=new ElementsHolder(); 
    if (view==null){ 
     LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     view = layoutInflater.inflate(R.layout.own_event_list,parent,false); 
     elemetsHolder.tx_Event=(TextView) view.findViewById(R.id.event_name); 
     elemetsHolder.tx_Date=(TextView) view.findViewById(R.id.event_date); 
     view.setTag(elemetsHolder); 
    } 
    else 
    { 
     elemetsHolder=(ElementsHolder) view.getTag(); 

    } 
    Own_EventListElements own_eventListElements=(Own_EventListElements)this.getItem(position); 
    elemetsHolder.tx_Event.setText(own_eventListElements.getEvent()); 
    elemetsHolder.tx_Date.setText(own_eventListElements.getDate()); 

    return view; 
} 

static class ElementsHolder 
{ 
    TextView tx_Event,tx_Date; 
} 

}

，这里是PHP文件

$con = mysqli_connect($server_name, $mysql_user, $mysql_pass, $db_name); 
$user_id = $_POST["user_id"]; 
$sql_query = "select event_id, event, event_type, date, user_id from events where user_id like '$user_id'"; 
$result = mysqli_query($con,$sql_query); 
$response = array(); 
while($row = mysqli_fetch_array($result)) 
{ 
array_push($response,array("event_id"=>$row[0],"event"=>$row[1],"event_type"=>$row[2],"date"=>$row[3],"user_id"=>$row[4])); 
} 
echo json_encode(array("server_response"=>$response)); 

mysqli_close($con);

，但它给我错误

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference

请帮助我。在此先感谢

编辑：这里是我初始化这个

View view = inflater.inflate(R.layout.fragment_news_feed, container, false); 
    ListView listEvents = (ListView) view.findViewById(R.id.listEvents1); 

    return view;

logcat的

FATAL EXCEPTION: main 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime: Process: com.example.bebo, PID: 17664 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at com.example.bebo.eventsFragment.ParseJson(eventsFragment.java:230) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at com.example.bebo.eventsFragment$BackgroundSearchEvents.onPostExecute(eventsFragment.java:221) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at com.example.bebo.eventsFragment$BackgroundSearchEvents.onPostExecute(eventsFragment.java:155) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.os.AsyncTask.finish(AsyncTask.java:636) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.os.AsyncTask.access$500(AsyncTask.java:177) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:111) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:194) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5653) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960) 
05-14 11:37:00.733 17664-17664/com.example.bebo E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

来源

2016-05-14 bebo

它说你的'ListView'是** **空。 “setAdapter（）”的代码在哪里列出？ –

但是thera是数据库中的值，请告诉我如何解决它？我的技术使用数组有什么错误吗？ @jankigadhiya – bebo

@jankigadhiya setAdapter是android studio中的内置函数，用于设置结果列表的适配器 – bebo

初始化列表中的onCreate（）：

listEvents = (ListView)findViewById(R.id.list_id);

更改ParseJson（）方法是这样的：

public void ParseJson() { 

if (json_string == null) { 
    Toast.makeText(getActivity(), "No Events", Toast.LENGTH_LONG).show(); 
} else { 

    adapterOwnEvents = new AdapterOwnEvents(getActivity(), R.layout.own_event_list); 
    listEvents.setAdapter(adapterOwnEvents); 
    try { 
     jsonObject = new JSONObject(json_string); 
     jsonArray = jsonObject.getJSONArray("server_response"); 

     int count = 0; 
     String event_id, event, event_type, date, image, friend_id; 
     while (count < jsonArray.length()) { 
      JSONObject JO = jsonArray.getJSONObject(count); 
      event_id = JO.getString("event_id"); 
      event = JO.getString("event"); 
      date = JO.getString("date"); 
      event_type = JO.getString("event_type"); 
      friend_id = JO.getString("user_id"); 
      image = ("http://example.com/uploads/" + friend_id + ".png"); 

      Own_EventListElements own_eventListElements = new Own_EventListElements(event_id, event, event_type, date, image); 
      adapterOwnEvents.add(own_eventListElements); 
      listEvents.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
       public void onItemClick(AdapterView<?> parent, View view, 
             int position, long id) { 

        Own_EventListElements eventsElements = (Own_EventListElements) adapterOwnEvents.getItem(position); 
        Intent i = new Intent(getActivity(), SendGreetings.class); 

        startActivity(i); 
       } 
      }); 
      count++; 
     } 


    } catch (JSONException e) { 
     e.printStackTrace(); 
    } 
} 
}

尝试使你的ListView全球

编辑：致电SearchFriends()在onCreateView（）

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    // Inflate the layout for this fragment 
    View view = inflater.inflate(R.layout.fragment_news_feed, container, false); 
    listEvents = (ListView) view.findViewById(R.id.listEvents1); 
    noevents = (TextView) view.findViewById(R.id.noEvents); 
    SearchFriends(); 
    return view; 
} 

@Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 
}

来源

2016-05-14 05:06:53

我试过这个，但它不工作。再次显示相同的错误 – bebo

你在哪里初始化'listEvents'？这是listview对吗？分享该代码..你正在做'findViewById（）'？ –

是的检查我更新的问题，我在最后 – bebo

你不设置适配器之前，初始化你ParsJson方法adapterOwnEvents。

adapterOwnEvents = new AdapterOwnEvents(getActivity(), R.layout.own_event_list); 
    listEvents.setAdapter(adapterOwnEvents);

代替

listEvents.setAdapter(adapterOwnEvents); 
    adapterOwnEvents = new AdapterOwnEvents(getActivity(), R.layout.own_event_list); 
    listEvents.setAdapter(adapterOwnEvents);

，我建议你使用GSON库解析JSON。

来源

2016-05-14 05:01:57

我没有收到你..你能解释吗？ – bebo

我现在试过，但显示相同的错误。 – bebo

将数组传递给doInBackground函数并从中获取结果？

回答

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