我正在尝试解析 json 对象以将其填充到列表视图中，但我遇到了一些问题，请帮忙
我收到 NullpointerException
这是我的完整代码：
我正在从以下 url 解析数据
解析数据的代码
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
public JSONParser(){
}
public JSONObject getJSONFromUrl(String url){
//making Http request
try{
//default httpclient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
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 parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
here is activity code
public class AndroidJSONParsingActivity extends ListActivity {
// url to make request
private static String url = "http://www.kaverisoft.com/careers/assignments/android/a1.php";
// JSON NAme Node
private static final String TAG_BOOK = "book";
private static final String TAG_ID = "id";
private static final String TAG_TITLE = "title";
private static final String TAG_AUTHORS = "authors";
private static final String TAG_DESCRIPTION = "description";
private static final String TAG_PRICE = "price";
//Book JSONArray
JSONArray book = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// HashMap for ListView
ArrayList<HashMap<String, String>> bookList = new ArrayList<HashMap<String, String>>();
// creating Json parser instance
JSONParser jParser = new JSONParser();
// getting Json String from url
JSONObject json = jParser.getJSONFromUrl(url);
try{
// getting array of books
book = json.getJSONArray(TAG_BOOK);
// looping through all books
for(int i=0;i<book.length();i++){
JSONObject c = book.getJSONObject(i);
// storing each json item in variable
String title = c.getString(TAG_TITLE);
String price = c.getString(TAG_PRICE);
String authors = c.getString(TAG_AUTHORS);
String id = c.getString(TAG_ID);
String description = c.getString(TAG_DESCRIPTION);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_ID, id);
map.put(TAG_TITLE, title);
map.put(TAG_PRICE, price);
map.put(TAG_AUTHORS, authors);
map.put(TAG_DESCRIPTION, description);
bookList.add(map);
}
}
catch (JSONException e) {
e.printStackTrace();
}
// Updating Parsed Data into ListView
ListAdapter adapter = new SimpleAdapter(this, bookList,
R.layout.list_item,
new String[]{TAG_TITLE,TAG_DESCRIPTION,TAG_AUTHORS } , new int[] {
R.id.title,R.id.description,R.id.author });
setListAdapter(adapter);
// selecting single list view item
ListView lv = getListView();
// Launching new screen on Selecting Single ListItem
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String title = ((TextView) view.findViewById(R.id.title)).getText().toString();
String authors = ((TextView) view.findViewById(R.id.author)).getText().toString();
String description = ((TextView) view.findViewById(R.id.description)).getText().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
in.putExtra(TAG_TITLE, title);
in.putExtra(TAG_AUTHORS, authors);
in.putExtra(TAG_DESCRIPTION, description);
startActivity(in);
}
});
}
}
我正在尝试仅解析书籍对象
请解决我的问题。
LogCat 详细信息
08-24 00:56:48.202: W/dalvikvm(949): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
08-24 00:56:48.263: E/AndroidRuntime(949): FATAL EXCEPTION: main
08-24 00:56:48.263: E/AndroidRuntime(949): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sree.androidjsonparser/com.sree.androidjsonparser.AndroidJSONParsingActivity}: java.lang.NullPointerException
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.os.Handler.dispatchMessage(Handler.java:99)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.os.Looper.loop(Looper.java:123)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread.main(ActivityThread.java:4627)
08-24 00:56:48.263: E/AndroidRuntime(949): at java.lang.reflect.Method.invokeNative(Native Method)
08-24 00:56:48.263: E/AndroidRuntime(949): at java.lang.reflect.Method.invoke(Method.java:521)
08-24 00:56:48.263: E/AndroidRuntime(949): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-24 00:56:48.263: E/AndroidRuntime(949): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-24 00:56:48.263: E/AndroidRuntime(949): at dalvik.system.NativeStart.main(Native Method)
08-24 00:56:48.263: E/AndroidRuntime(949): Caused by: java.lang.NullPointerException
08-24 00:56:48.263: E/AndroidRuntime(949): at com.sree.androidjsonparser.AndroidJSONParsingActivity.onCreate(AndroidJSONParsingActivity.java:62)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-24 00:56:48.263: E/AndroidRuntime(949): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
08-24 00:56:48.263: E/AndroidRuntime(949): ... 11 more
08-24 00:56:53.812: I/Process(949): Sending signal. PID: 949 SIG: 9