使用AsynTask从JSON显示Listview

Question

使用listview从JSON显示asyntask时出现问题。我希望在特定radiobutton点击下显示数据，但DDMS结果显示为"Caused by: java.lang.NullPointerException"。

ListResult.java

public class ListResult extends ListActivity implements OnClickListener {
private ProgressDialog pDialog;
String paramString;
JSONParser jsonParser = new JSONParser();
ArrayList<HashMap<String, String>> busList; 
RadioButton rbSUN;
RadioButton rbFRI;
RadioButton rbSAT;
ListView lv;
private int success;
private static String url_insert_new = "http://10.0.2.2/onlineLibrary/getallbus.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_IDIOMS = "idioms";
private static final String TAG_ID = "id";
private static final String TAG_TIME = "time";
private static final String TAG_STATUS = "status";  
JSONArray idioms = null;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_result);
    busList = new ArrayList<HashMap<String, String>>();  
    lv = getListView();
    rbSUN = (RadioButton) findViewById(R.id.radioSUN);
    rbFRI = (RadioButton) findViewById(R.id.radioFRI);
    rbSAT = (RadioButton) findViewById(R.id.radioSAT);
    rbSUN.setOnClickListener(this);
    rbFRI.setOnClickListener(this);
    rbSAT.setOnClickListener(this);   
    new InsertNewIdiom().execute();
}
@Override
public void onClick(View v) {
    if (v.getId()==R.id.radioSUN){
        new InsertNewIdiom().execute();
        if (success==1){
            Toast.makeText(getApplicationContext(), "New item saved...", Toast.LENGTH_LONG).show();
        }else{
            Toast.makeText(getApplicationContext(), "New item FAILED to saved...", Toast.LENGTH_LONG).show();
        }
        paramString="SUN";
    }    
    if (v.getId()==R.id.radioFRI){
        new InsertNewIdiom().execute();
        if (success==1){
            Toast.makeText(getApplicationContext(), "New item saved...", Toast.LENGTH_LONG).show();
        }else{
            Toast.makeText(getApplicationContext(), "New item FAILED to saved...", Toast.LENGTH_LONG).show();
        }
        paramString="FRI";
    }
    if (v.getId()==R.id.radioSAT){
        new InsertNewIdiom().execute();
        if (success==1){
            Toast.makeText(getApplicationContext(), "New item saved...", Toast.LENGTH_LONG).show();
        }else{
            Toast.makeText(getApplicationContext(), "New item FAILED to saved...", Toast.LENGTH_LONG).show();
        }
        paramString="SAT";
    } 
}
class InsertNewIdiom extends AsyncTask<String, String, String> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(ListResult.this);
        pDialog.setMessage("Loading ...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }
    protected String doInBackground(String... args) {
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("time", TAG_TIME));
        params.add(new BasicNameValuePair("status", TAG_STATUS));
        JSONObject json = jsonParser.makeHttpRequest(url_insert_new,
                "GET", params);
        Log.d("Insert New item Response", json.toString());
        try {
            success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                  idioms = json.getJSONArray(TAG_IDIOMS);
                  for (int i = 0; i < idioms.length(); i++) {
                      JSONObject c = idioms.getJSONObject(i);
                      String id = c.getString(TAG_ID);
                      String time = c.getString(TAG_TIME);
                      String status = c.getString(TAG_STATUS);
                      HashMap<String, String> map = new HashMap<String, String>();
                      map.put(TAG_ID, id);
                      map.put(TAG_TIME, time);
                      map.put(TAG_STATUS, status);
                      busList.add(map);
                  }               
            } else {
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }
    protected void onPostExecute(String file_url) {
        pDialog.dismiss();
       // pDialog.dismiss();
        runOnUiThread(new Runnable() {
            public void run() {
                ListAdapter adapter = new SimpleAdapter(
                        ListResult.this, busList,
                        R.layout.list_view, new String[] 
{ TAG_ID,   TAG_TIME, TAG_STATUS},
                        new int[] { R.id.id, R.id.time, R.id.status});
               setListAdapter(adapter);
            }
        });
    }
}
}

JsonParser.java

public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
public JSONParser() {

}
public JSONObject makeHttpRequest(String url, String method,
        List<NameValuePair> params) {
    try {
        if(method == "POST"){
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        }else if(method == "GET"){
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }           

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    return jObj;

 }

 }

activity_list_result.xml

    <LinearLayout xmlns:android=
   "http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical" >

  <ScrollView 
    android:id="@+id/scrollView1"
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_gravity="center" 

    >

  <LinearLayout
   android:layout_width="match_parent"
   android:layout_height="wrap_content"      
   android:orientation="vertical" 

   >
  <LinearLayout
   android:layout_width="match_parent"
   android:layout_height="wrap_content"      
   android:orientation="vertical" 
   android:background="#B3E5FC"
   >
  <TextView
    android:id="@+id/textGranular"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:text="BUS Schedule:"
    android:textAppearance="?android:attr/textAppearanceMedium" 
    android:textColor="#0000ff"
    android:padding="7dp"
    android:textStyle="italic"
    />

   <HorizontalScrollView
    android:id="@+id/horizontalScrollView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal" >


    <RadioGroup
        android:id="@+id/radioGroup1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <RadioButton
            android:id="@+id/radioSUN"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checked="true"
            android:text="Sunday-Thursday" />

        <RadioButton
            android:id="@+id/radioFRI"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"                
            android:text="Friday" />

        <RadioButton
            android:id="@+id/radioSAT"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Saturnday" />


      </RadioGroup>
    </LinearLayout>
    </HorizontalScrollView>
       </LinearLayout>

   <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:orientation="vertical" >

    <ListView
    android:id="@android:id/list"
    android:layout_width="wrap_content"
    android:layout_height="396dp" >
    </ListView>

       </LinearLayout>  
  </LinearLayout>    
   </ScrollView>

   </LinearLayout> 

list_view.xlm

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >

<TextView
    android:id="@+id/id"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:visibility="gone" />

 <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:weightSum="6"
    >

     <TextView
         android:id="@+id/textView2"
         android:layout_width="57dp"
         android:layout_height="wrap_content"
         android:padding="2dp"
         android:text="Time:"
         android:textAppearance="?android:attr/textAppearanceMedium"
         android:textColor="#000"
         android:textSize="14sp" />

    <TextView
        android:id="@+id/time"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="2dp"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textColor="#000"
        android:textSize="14sp" />

       </LinearLayout>


 <!-- Entry data display -->
 <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:weightSum="6"
    >       
     <TextView
         android:id="@+id/textView3"
         android:layout_width="57dp"
         android:layout_height="wrap_content"
         android:padding="2dp"
         android:text="Status:"
         android:textAppearance="?android:attr/textAppearanceMedium"
         android:textColor="#000"
         android:textSize="14sp" />

    <TextView
        android:id="@+id/status"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="2dp"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textColor="#000"
        android:textSize="14sp" />       
       </LinearLayout> 
</LinearLayout>

getallbus.php

  <?php
  $response=array();
  $paramString=$_REQUEST[''];

  require_once __DIR__.'/db_connect.php';
  $db=new DB_CONNECT();
  $sql="SELECT * FROM getbus WHERE day='$paramString'";

  $result=mysql_query($sql);

   if(!empty($result))
  {
    if(mysql_num_rows($result)>0)
    {
        $response['idioms']=array();
       while ($row = mysql_fetch_array($result)) {
            $book=array();
            $book['day']=$row['day'];
            $book['time']=$row['time'];
            $book['status']=$row['status'];

            array_push($response['idioms'], $book);
        }
        $response['success']=1;
        echo json_encode($response);
    }
    else {
        $response['success']=0;
        $response['message']='No data found';

        echo json_encode($response);
    }
  }
 ?>

logcat的

02-07 14:37:09.761: E/JSON Parser(1195): Error parsing data org.json.JSONException: Value <br of type java.lang.String cannot be converted to JSONObject 
02-07 14:37:19.091: E/JSON Parser(1195): Error parsing data org.json.JSONException: Value <br of type java.lang.String cannot be converted to JSONObject 

Answer 1

您的PHP文件失败，反过来，显示的异常（作为HTML数据，因为它是一个PHP文件）被传递回您的应用程序，而不是检查成功代码。由于您的应用程序只是获取数据并运行它，它正在尝试将您的PHP文件中的异常解析为JSON，这显然不起作用。您需要在PHP文件中验证不会抛出任何异常并且它会提供有效的JSON响应。

就您的PHP异常而言，您尝试访问$_REQUEST中不存在的数组索引，因为您将空字符串传递给[]。这导致您的PHP文件失败。当PHP抛出一个异常时，它会给出一个描述错误的默认响应（作为HTML），而你的应用程序正试图将其解析为JSON，并且失败了。

因此，如果您将请求发送到PHP文件

getallbus.php?requestParam=[yourRequestParam] // aka `GET`

然后你会用

$paramString = $_GET['requestParam']; 

如果您将请求作为POST发送，则可以使用

$paramString = $_POST['requestParam'];

这样，只要实际存在名为“requestParam”的索引，PHP就不应抛出异常。希望这会有所帮助。