自定义ArrayAdapter抛出NullPointerException

Question

这可能是一个facepalm但我已经搜索了一个多星期了。

我在ListFragment中使用了自定义ArrayAdapter。一旦我在listview上设置了adapter它会抛出一个NPE，但我无法弄清楚为什么我的适配器没有返回任何东西。

JobAttachedTasks.java

package com.calnetwork;

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

import library.com.calnetwork.JSONParser;
import library.com.calnetwork.TaskAttachedItemAdapter;

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

import android.app.ProgressDialog;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class JobAttachedTasks extends ListFragment {

    public JobAttachedTasks() {}

    // Progress Dialog
    private ProgressDialog pDialog;
    public String jobID, taskID;


 // Creating JSON Parser object
    JSONParser jParser = new JSONParser();

    // JSON Node names
    private static final String TAG_JOB_JOBID = "jobID";
    private static final String TAG_JOB_TASKID = "taskID"; 
    private static final String TAG_JOB_TASKID_TITLE = "taskTitle"; 
    private static final String TAG_JOB_INSTRUMENT_NAME = "instrumentName";
    private static final String TAG_JOB_TASK_TYPE = "taskType";    
    private static final String TAG_SUCCESS = "success";

    public JSONArray tasks = null;
    public ListView lv;
    public Button options;
    public ArrayList<HashMap<String, String>> taskList = new ArrayList<HashMap<String, String>>();
    public TaskAttachedItemAdapter myAdapter = null;
    // JSON parser class
    JSONParser jsonParser = new JSONParser();

    // URL to get job details
    private static final String display_attached_tasks_url = "http://com.tradeport.on.ca/view_tasks_attached_to_job.php"; 

    // URL to remove selected task
    private static final String remove_task_url = "http://com.tradeport.on.ca/delete_single_attached_task.php"; 



    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View rootView = inflater.inflate(R.layout.job_attached_task, container, false);
        getActivity().getActionBar().setTitle("Edit Job Details");
        getActivity().getActionBar().setHomeButtonEnabled(true);


        Intent i = getActivity().getIntent();
        jobID = i.getStringExtra("jobID");
        taskList = new ArrayList<HashMap<String, String>>();
        ListView lv = (ListView) rootView.findViewById(android.R.id.list);
        myAdapter = new TaskAttachedItemAdapter(getActivity(), R.layout.list_job_attached_item, taskList);
        lv.setAdapter(myAdapter);
        lv.setOnItemLongClickListener(null);
        registerForContextMenu(lv);

        new LoadAllTasks().execute();
        return rootView;    


    }

    @Override
    public boolean onOptionsItemSelected(MenuItem menuItem)
    {       
        getActivity().onBackPressed();
        return true;
    }


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

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(getActivity());
            pDialog.setMessage("Loading attached tasks. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        /**
         * getting All products from url
         * @return 
         * */
        protected String doInBackground(String... args) {
            // Building Parameters

            SharedPreferences pref = getActivity().getApplicationContext().getSharedPreferences("USER_SESSION", 0);
            String session_username = pref.getString("username", null);
            String session_key = pref.getString("key", null);

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("tag", "view_attached_tasks"));
            params.add(new BasicNameValuePair("username", session_username));
            params.add(new BasicNameValuePair("key", session_key ));
            params.add(new BasicNameValuePair("jobID", jobID));

          Log.d("task query params: ", params.toString());

            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest(display_attached_tasks_url, "POST", params);

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

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

                if (success == 1) {
                    // products found
                    // Getting Array of users
                    tasks = json.getJSONArray("tasks");
                    Log.d("Single Attached Tasks Details", tasks.toString());

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

                        // Storing each json item in variable
                        String taskID = c.getString(TAG_JOB_TASKID);
                        String instrumentName = c.getString(TAG_JOB_INSTRUMENT_NAME);
                        String taskType = c.getString(TAG_JOB_TASK_TYPE);

                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        map.put(TAG_JOB_TASKID, taskID);
                        map.put(TAG_JOB_JOBID, jobID);
                        map.put(TAG_JOB_TASKID_TITLE, "Task ID : "+taskID);
                        map.put(TAG_JOB_INSTRUMENT_NAME, instrumentName);
                        map.put(TAG_JOB_TASK_TYPE, taskType);

                        // adding HashList to ArrayList
                        taskList.add(map);
                    }
                } else {

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

            return null;
        }


        public void onPostExecute(String args) {
            // dismiss the dialog after getting all products
            pDialog.dismiss();
            // updating UI from Background Thread
           Log.d("taskList", taskList.toString());
            myAdapter = new TaskAttachedItemAdapter(getActivity(), R.layout.list_job_attached_item, taskList);
            lv.setAdapter(myAdapter);

        }
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);

        menu.add(0, 0, 0, "Task Details");
        menu.add(0, 1, 0,"Remove Task");

        return;

    }



    @Override
    public boolean onContextItemSelected(MenuItem item) {
        super.onContextItemSelected(item);

        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();

        taskID = ((TextView) info.targetView.findViewById(R.id.taskID)).getText().toString();
        int menuPosition = item.getItemId();
        Object itemIndex = taskList.get(menuPosition);


        if(item.getTitle().equals("Task Details")) { 

            Intent i = new Intent(getActivity().getApplicationContext(), Tasks.class);
            i.putExtra("taskID", taskID);
            startActivity(i);

        } else if(item.getTitle().equals("Remove Task")) {

            taskList.remove(itemIndex);

            myAdapter.notifyDataSetChanged();


        } 
        return true;
    };

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


        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(getActivity());
            pDialog.setMessage("Deleting User ...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        /**
         * Saving product
         * */
        protected String doInBackground(String... args) {

            SharedPreferences pref = getActivity().getSharedPreferences("USER_SESSION", 0);
            String session_username = pref.getString("username", null);
            String session_key = pref.getString("key", null);


            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("tag", "delete_single_attached_task"));
            params.add(new BasicNameValuePair("taskID", taskID));
            params.add(new BasicNameValuePair("jobID", String.valueOf(jobID)));
            params.add(new BasicNameValuePair("session_username", session_username));
            params.add(new BasicNameValuePair("session_key", session_key));

            Log.d("delete params", String.valueOf(params));

            JSONObject json = jsonParser.makeHttpRequest(remove_task_url, "POST", params);

            // check json success tag
            try {
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // successfully updated


                } else {
                    // failed to update product
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog once product uupdated
            pDialog.dismiss();

            Toast.makeText(getActivity(), "Task Removed Successfully",Toast.LENGTH_SHORT).show();

        }
    }

}

TaskAttachedAdapter.java

package library.com.calnetwork;

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

import com.calnetwork.R;

import android.content.ClipData.Item;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class TaskAttachedItemAdapter extends ArrayAdapter<String> {

     public static LayoutInflater inflater = null;
     public ArrayList<HashMap<String, String>> taskList;
     public String jobId;
     public Context context;
     public int layoutResourceId;


    static class ViewHolder {

        TextView jid;
        TextView tid;
        TextView tidt;
        TextView ti;
        TextView tt;

      }

    public TaskAttachedItemAdapter(Context context, int layoutResourceId){

        super(context, layoutResourceId);
        this.context = context;
        Log.d("taskAttachedItemAdapter 1", "check");
    }

    public TaskAttachedItemAdapter(Context context, int layoutResourceId, ArrayList<HashMap<String, String>> taskList){

        super(context, layoutResourceId);
        this.context = context;
        this.taskList = taskList;
        Log.d("taskAttachedItemAdapter 2", "check");
    }

    @Override
    public int getCount() {
        return taskList.size();
    }

    public Item getItem(Item position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position; 
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Log.d("taskAttachedItemAdapter 3", "check");
        ViewHolder holder = null;
        View v = convertView;
        if(convertView == null)
        {
            Log.d("taskAttachedItemAdapter 4", "check");
            LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = inflater.inflate(R.layout.list_job_attached_item, null);
            TextView jid = (TextView) v.findViewById(R.id.jobID);
            TextView tidt = (TextView) v.findViewById(R.id.attachedTaskID);
            TextView tid = (TextView) v.findViewById(R.id.taskID);
            TextView ti = (TextView) v.findViewById(R.id.taskInstrument);
            TextView tt = (TextView) v.findViewById(R.id.taskType);
            v.setTag(holder);
        }

        HashMap<String, String> i = taskList.get(position);

        if(i != null)
        {
            Log.d("taskAttachedItemAdapter 5", "check");

            holder = (ViewHolder) v.getTag();
            String sjid = i.get("jobID");
            String stidt = i.get("taskTitle");
            String stid = i.get("taskID");
            String sti = i.get("instrumentName");
            String stt = i.get("taskType");

            holder.jid.setText(sjid);
            holder.tidt.setText(stidt);
            holder.tid.setText(stid);
            holder.ti.setText(sti);
            holder.tt.setText(stt);


        }

        return v;


    }

}

list_job_attached_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:paddingTop="6dip"
    android:paddingBottom="6dip" >

    <!-- Job id and task id - will be HIDDEN - used to pass to other activity -->

    <TextView
        android:id="@+id/taskID"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:visibility="gone" />
    <TextView
        android:id="@+id/jobID"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:visibility="gone" />
    <!-- Name Label -->

    <TextView
        android:id="@+id/whiteBackground"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_marginTop="10dp"
        android:layout_alignParentBottom="true"
        android:background="@drawable/white_field_with_stroke" />

     <TextView
        android:id="@+id/greenBackground"
        android:layout_width="fill_parent"
        android:layout_height="25dp"
        android:layout_marginTop="4dp"
        android:layout_marginLeft="3dp"
        android:layout_marginRight="50dp"
        android:background="@color/list_item_title" />




    <TextView
        android:id="@+id/attachedTaskID"
        android:layout_width="fill_parent"
        android:layout_height="30dp"
        android:layout_marginTop="4dp"
        android:layout_marginLeft="3dp"
        android:layout_marginRight="50dp"
        android:padding="5dp"
        android:textColor="#ffffff"
        android:text="Task ID : 4"
        android:textSize="12sp" />

    <LinearLayout
    android:id="@+id/labelContainer"    
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:layout_below="@id/attachedTaskID"
    android:layout_marginTop="5dp">

        <TextView
            android:id="@+id/instrumentLabel"
            android:layout_width="0dp"
            android:layout_weight=".50" 
            android:layout_height="wrap_content"
            android:layout_marginLeft="10dp"
            android:text="instrument :"
            android:textColor="#999999"
            android:textSize="9sp" />

        <TextView
            android:id="@+id/taskTypeLabel"
            android:layout_width="0dp"
            android:layout_weight=".50"
            android:layout_height="wrap_content"
            android:textColor="#999999"
            android:text="task type"
            android:textSize="9sp" />


    </LinearLayout>

    <LinearLayout
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:layout_below="@id/labelContainer"
    android:layout_marginTop="5dp">

         <TextView
            android:id="@+id/taskInstrument"
            android:layout_width="0dp"
            android:layout_weight=".50"
            android:layout_height="wrap_content"
            android:padding="5dp"
            android:textColor="#000000"
            android:text="GW Instek GDS 3220"
            android:textSize="12sp" />

        <TextView
            android:id="@+id/taskType"
            android:layout_width="0dp"
            android:layout_weight=".50"
            android:layout_height="wrap_content"
            android:text="Accredited Calibration"
            android:textColor="#000000"
            android:textSize="12sp" />

    </LinearLayout>



</RelativeLayout>

最后是logCat错误输出

02-12 19:41:49.225: E/AndroidRuntime(4456): FATAL EXCEPTION: main
02-12 19:41:49.225: E/AndroidRuntime(4456): java.lang.NullPointerException
02-12 19:41:49.225: E/AndroidRuntime(4456):     at com.calnetwork.JobAttachedTasks$1.onClick(JobAttachedTasks.java:284)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at android.os.Looper.loop(Looper.java:137)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at android.app.ActivityThread.main(ActivityThread.java:5041)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at java.lang.reflect.Method.invokeNative(Native Method)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at java.lang.reflect.Method.invoke(Method.java:511)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-12 19:41:49.225: E/AndroidRuntime(4456):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

别介意人们。找到了答案。我的ListView和taskList声明是Null指针异常的原因。万一有人需要知道我做了什么来清理它，这是。

对于我的taskList ArrayList，改变了这个：

public ArrayList<HashMap<String, String>> taskList = new ArrayList<HashMap<String, String>>();

对此：

public ArrayList<HashMap<String, String>> taskList;

对于我的lv ListView，更改了这个：

ListView lv = (ListView) rootView.findViewById(android.R.id.list);

对此：

lv = (ListView) rootView.findViewById(android.R.id.list);

我还对arrayAdapter进行了更新。

public class TaskAttachedItemAdapter extends ArrayAdapter<String> {

 public static LayoutInflater inflater = null;
 public ArrayList<HashMap<String, String>> taskList;
 public String jobId;
 public Context context;
 public int layoutResourceId;


public static class ViewHolder {

    TextView jid;
    TextView tid;
    TextView tidt;
    TextView ti;
    TextView tt;

  }

public TaskAttachedItemAdapter(Context context, int layoutResourceId){

    super(context, layoutResourceId);
    this.context = context;
}

public TaskAttachedItemAdapter(Context context, int layoutResourceId, ArrayList<HashMap<String, String>> taskList){

    super(context, layoutResourceId);
    this.context = context;
    this.taskList = taskList;
}

@Override
public int getCount() {
    return taskList.size();
}

public Item getItem(Item position) {
    return position;
}

@Override
public long getItemId(int position) {
    return position; 
}

@Override
public boolean hasStableIds() {
    return true;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    HashMap<String, String> i = taskList.get(position);
    ViewHolder holder = null;
    View v = convertView;

    if(convertView == null)
    {
        LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = inflater.inflate(R.layout.list_job_attached_item, null);
        TextView jid = (TextView) v.findViewById(R.id.jobID);
        TextView tidt = (TextView) v.findViewById(R.id.attachedTaskID);
        TextView tid = (TextView) v.findViewById(R.id.taskID);
        TextView ti = (TextView) v.findViewById(R.id.taskInstrument);
        TextView tt = (TextView) v.findViewById(R.id.taskType);
        v.setTag(holder);
    }


    //holder = (ViewHolder) convertView.getTag();

    if(i != null)
    {

        TextView jid = (TextView) v.findViewById(R.id.jobID);
        TextView tidt = (TextView) v.findViewById(R.id.attachedTaskID);
        TextView tid = (TextView) v.findViewById(R.id.taskID);
        TextView ti = (TextView) v.findViewById(R.id.taskInstrument);
        TextView tt = (TextView) v.findViewById(R.id.taskType);

        String sjid = i.get("jobID");
        String stidt = i.get("taskTitle");
        String stid = i.get("taskID");
        String sti = i.get("instrumentName");
        String stt = i.get("taskType");

        jid.setText(sjid);
        tidt.setText(stidt);
        tid.setText(stid);
        ti.setText(sti);
        tt.setText(stt);


    }

    return v;


}

}