php - eclipse 在 InBackground 方法中显示错误我不知道如何修复它

Question

我有一个android应用程序，需要使用php在android和mysql数据库之间进行连接，该应用程序工作完美。只有显示用户操作不起作用，此方法在包含一些数据的列表中显示用户。

谁能帮我解决这个错误？

LogCat 错误

       04-14 21:37:37.378: E/AndroidRuntime(1854): Caused by: java.lang.NullPointerException
04-14 21:37:37.378: E/AndroidRuntime(1854):     at com.devleb.loginDemo.UserListActivity$getUserList.doInBackground(UserListActivity.java:143)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at com.devleb.loginDemo.UserListActivity$getUserList.doInBackground(UserListActivity.java:1)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
04-14 21:37:37.378: E/AndroidRuntime(1854):     ... 4 more

用户.java

package com.devleb.loginDemo;

import java.util.HashMap;

//@SuppressWarnings("serial")
public class User extends HashMap<String, String> {

    /**
     * 
     */
    String name;
    String date;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

}

自定义适配器.java

package com.devleb.loginDemo;

import java.util.ArrayList;
import java.util.Date;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

public class CustomAdapter extends BaseAdapter {

    private static ArrayList<User> usersList;

    // private static ArrayList name, date;
    LayoutInflater layoutInflater;
    String[] userName;
    Date[] createdDate;
    Context context;

    @SuppressWarnings("rawtypes")
    public CustomAdapter(ArrayList<User> result, Context c) {
        usersList = result;
        context = c;

    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return usersList.size();
    }

    @Override
    public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return usersList.get(arg0);
    }

    @Override
    public long getItemId(int arg0) {
        // TODO Auto-generated method stub
        return arg0;
    }

    @Override
    public View getView(int position, View arg1, ViewGroup parent) {
        // TODO Auto-generated method stub

        layoutInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View row = null;

        row = layoutInflater.inflate(R.layout.list_item, parent, false);
        TextView txtCreateDate = (TextView) row
                .findViewById(R.id.txtCreateDate);

        txtCreateDate.setText(usersList.get(position).getDate().toString());

        TextView txtName = (TextView) row.findViewById(R.id.name);

        txtName.setText(usersList.get(position).getName());
        return row;
    }

}

UserListActivity.java

package com.devleb.loginDemo;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class UserListActivity extends ListActivity {

    JSONParser jsonParser = new JSONParser();

    // ArrayList<HashMap<String, String>> usersList;

    // **** added from internt*************///
    @SuppressWarnings("rawtypes")
    ArrayList<User> arrayList_userList;
    ListView lvUsers;
    // **** added from internt*************///

    private static String url_display_user = "http://10.0.3.2/android_connect/display_user.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_MESSAGE = "message";

    private static final String TAG_ID = "id";

    private static final String TAG_USERS = "userlist";

    private static final String TAG_USER = "user";
    private static final String TAG_DATE = "date";

    // private static final String TAG_NAME = "name";

    // employees JSONArray
    JSONArray users = null;

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

        // usersList = new ArrayList<HashMap<String, String>>();

        new getUserList().execute();

        // getListView
        lvUsers = (ListView) findViewById(android.R.id.list);

        lvUsers.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> arg0, View view, int arg2,
                    long arg3) {

                // String id = ((TextView)
                // view.findViewById(R.id.uid)).getText()
                // .toString();

                // Intent in = new Intent(getBaseContext(), StatusList.class);
                // in.putExtra(TAG_ID, uid);

                // startActivity(in);
            }
        });
    }

    class getUserList extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            UserListActivity.this.setProgressBarIndeterminateVisibility(true);
        }

        @Override
        protected String doInBackground(String... params) {
            // TODO Auto-generated method stub

            // Building Parameters
            List<NameValuePair> parametres = new ArrayList<NameValuePair>();
            // getting JSON string from URL
            JSONObject json = jsonParser.makeHttpRequest(url_display_user,
                    "GET", parametres);

            // Check your log cat for JSON reponse
            Log.d("All Users: ", json.toString());

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // products found
                    // Getting Array of Products
                    users = json.getJSONArray(TAG_USERS);

                    // looping through All Users
                    for (int i = 0; i < users.length(); i++) {
                        JSONObject c = users.getJSONObject(i);

                        // Storing each json item in variable
                        String id = c.getString(TAG_ID);
                        String user = c.getString(TAG_USER);
                        String cdate = c.getString(TAG_DATE).toString();

                        // creating new HashMap
                        User map = new User();

                        // adding each child node to HashMap key => value
                        map.put(TAG_ID, id);
                        map.put(TAG_USER, user);
                        map.put(TAG_DATE, cdate);

                        // adding HashList to ArrayList

                        // usersList.add(map);

                        arrayList_userList.add(map);
                    }
                    // ***********************************//
                    // From the internet

                    // arrayList_userList = new
                    // ArrayList<User>(usersList.value())

                    // **********************************//

                    return json.getString(TAG_MESSAGE);
                } else {

                    return json.getString(TAG_MESSAGE);

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

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String result) {
            // dismiss the dialog after getting all products
            if (result != null) {

                UserListActivity.this
                        .setProgressBarIndeterminateVisibility(false);

                /**
                 * Updating parsed JSON data into ListView
                 * */
                /*
                 * ListAdapter adapter = new
                 * SimpleAdapter(UserListActivity.this, usersList,
                 * R.layout.list_item, new String[] { TAG_ID, TAG_USER }, new
                 * int[] { R.id.uid, R.id.name }); // updating listview
                 * setListAdapter(adapter);
                 */
                lvUsers.setAdapter(new CustomAdapter(arrayList_userList,
                        getBaseContext()));

                Toast.makeText(getBaseContext(), result, Toast.LENGTH_LONG)
                        .show();

            }
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.user_list, menu);
        return true;
    }

}

Answer 1

它会准确地告诉您错误所在。您遇到空指针异常。

来自你的日志猫:

04-14 21:37:37.378: E/AndroidRuntime(1854): Caused by: java.lang.NullPointerException
04-14 21:37:37.378: E/AndroidRuntime(1854):     at com.devleb.loginDemo.UserListActivity$getUserList.doInBackground(UserListActivity.java:143)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at com.devleb.loginDemo.UserListActivity$getUserList.doInBackground(UserListActivity.java:1)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-14 21:37:37.378: E/AndroidRuntime(1854):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
04-14 21:37:37.378: E/AndroidRuntime(1854):     ... 4 more

在 UserListActivity 第 143 行中，您似乎正在添加到 null ArrayList。快速浏览一下该类，您似乎从未初始化 arrayList_userList