将数组传递给doInBackground函数并从中获取结果？

Question

我想将一个数组传递给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搜索它。如果您不想帮助不要让它复制或让其他人不帮助我，请。 这是我试过的代码。

首先我从服务器数据库中获取值并解析它并希望将其存储在数组中。 整个碎片代码

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);

但它给了我错误

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

请帮帮我。提前谢谢

编辑： 这是我初始化这个

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

    return view; 

LOGCAT

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)

Answer 1

在ParsJson方法初始化adapterOwnEvents之前，你没有设置适配器。

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

而不是

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

我建议您使用Gson库来解析json。

Answer 2

在 onCreate（）：

中初始化您的列表

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

更改 ParseJson（）方法，如下所示：

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();
    }
}
}

  

尝试制作ListView Global

     

编辑：在 onCreateView（）

中致电SearchFriends()

    @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);
}