我正在将JSON解析为ArrayList，但每次都获得NPE，
at com.example.parsingjson.HotelAdapter.getCount（HotelAdapter.java:26）
return arrayList.size();
我的JSON看起来像这样：
{
"search": [
{
"country": "India",
"location": [
{
"title": "New Delhi",
"hotel": [
{
"name": "Hotel 5 Star"
},
{
"name": "Hotel Premium"
}
]
},
{
"title": "Bangalore",
"hotel": [
{
"name": "Hotel Comfort"
}
]
}
]
},
{
"country": "USA",
"location": [
{
"title": "California",
"hotel": [
{
"name": "Hotel Zone"
}
]
}
]
}
]
}
实际上我成功解析了JSON的前2级但是在尝试解析第三级JSON时获得 NullPointerException
和日志说：
06-21 16:28:52.310: D/AbsListView(9439): Get MotionRecognitionManager
06-21 16:28:52.460: D/libEGL(9439): loaded /system/lib/egl/libEGL_mali.so
06-21 16:28:52.490: D/libEGL(9439): loaded /system/lib/egl/libGLESv1_CM_mali.so
06-21 16:28:52.495: D/libEGL(9439): loaded /system/lib/egl/libGLESv2_mali.so
06-21 16:28:52.495: D/(9439): Device driver API match
06-21 16:28:52.495: D/(9439): Device driver API version: 10
06-21 16:28:52.495: D/(9439): User space API version: 10
06-21 16:28:52.495: D/(9439): mali: REVISION=Linux-r2p4-02rel0 BUILD_DATE=Tue Sep 25 15:06:14 KST 2012
06-21 16:28:52.515: D/OpenGLRenderer(9439): Enabling debug mode 0
06-21 16:28:53.405: D/dalvikvm(9439): GC_CONCURRENT freed 190K, 10% free 12379K/13703K, paused 2ms+26ms, total 45ms
06-21 16:28:55.540: D/GestureDetector(9439): [Surface Touch Event] mSweepDown False, mLRSDCnt : -1 mTouchCnt : 3 mFalseSizeCnt:0
06-21 16:28:55.630: D/batchname::(9439): USA
06-21 16:28:55.735: D/AbsListView(9439): Get MotionRecognitionManager
06-21 16:28:55.740: D/Location-fetchedname::(9439): USA
06-21 16:28:55.745: D/Location-checkdata:(9439): [com.example.parsingjson.Location@42780ab8]
06-21 16:28:55.865: E/SpannableStringBuilder(9439): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
06-21 16:28:55.865: E/SpannableStringBuilder(9439): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
06-21 16:28:57.470: D/GestureDetector(9439): [Surface Touch Event] mSweepDown False, mLRSDCnt : -1 mTouchCnt : 3 mFalseSizeCnt:0
06-21 16:28:57.570: D/dalvikvm(9439): GC_CONCURRENT freed 265K, 11% free 12543K/13959K, paused 5ms+4ms, total 30ms
06-21 16:28:57.805: D/AbsListView(9439): Get MotionRecognitionManager
06-21 16:28:57.805: D/Hotel-fetchedname::(9439): California
06-21 16:28:57.810: D/Hotel-checkdata:(9439): null
06-21 16:28:57.820: D/AndroidRuntime(9439): Shutting down VM
06-21 16:28:57.820: W/dalvikvm(9439): threadid=1: thread exiting with uncaught exception (group=0x41a052a0)
06-21 16:28:57.835: E/AndroidRuntime(9439): FATAL EXCEPTION: main
06-21 16:28:57.835: E/AndroidRuntime(9439): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.parsingjson/com.example.parsingjson.HotelActivity}: java.lang.NullPointerException
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread.access$700(ActivityThread.java:140)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.os.Handler.dispatchMessage(Handler.java:99)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.os.Looper.loop(Looper.java:137)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread.main(ActivityThread.java:4921)
06-21 16:28:57.835: E/AndroidRuntime(9439): at java.lang.reflect.Method.invokeNative(Native Method)
06-21 16:28:57.835: E/AndroidRuntime(9439): at java.lang.reflect.Method.invoke(Method.java:511)
06-21 16:28:57.835: E/AndroidRuntime(9439): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1036)
06-21 16:28:57.835: E/AndroidRuntime(9439): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:803)
06-21 16:28:57.835: E/AndroidRuntime(9439): at dalvik.system.NativeStart.main(Native Method)
06-21 16:28:57.835: E/AndroidRuntime(9439): Caused by: java.lang.NullPointerException
06-21 16:28:57.835: E/AndroidRuntime(9439): at com.example.parsingjson.HotelAdapter.getCount(HotelAdapter.java:26)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.widget.ListView.setAdapter(ListView.java:466)
06-21 16:28:57.835: E/AndroidRuntime(9439): at com.example.parsingjson.HotelActivity.onCreate(HotelActivity.java:42)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.Activity.performCreate(Activity.java:5191)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
06-21 16:28:57.835: E/AndroidRuntime(9439): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
06-21 16:28:57.835: E/AndroidRuntime(9439): ... 11 more
06-21 16:29:07.220: I/Process(9439): Sending signal. PID: 9439 SIG: 9
第一级： CountryActivity.java
@Override
protected Void doInBackground(Void... params) {
// url
jsonobjectMaps = JSONfunctions.getJSONfromURL("URL");
try {
arraylistSearch = new ArrayList<Search>();
JSONArray jsonArrayBatches = jsonobjectMaps.getJSONArray("search");
for (int i = 0; i < jsonArrayBatches.length(); i++) {
jsonobjectMaps = jsonArrayBatches.getJSONObject(i);
Search batches = new Search();
batches.setCountry(jsonobjectMaps.getString("country"));
arraylistStudent = new ArrayList<Location>();
JSONArray jsonArrayStudents = jsonobjectMaps.getJSONArray("location");
for (int j = 0; j < jsonArrayStudents.length(); j++) {
jsonobjectMaps = jsonArrayStudents.getJSONObject(j);
Location students = new Location();
students.setTitle(jsonobjectMaps.getString("title"));
arraylistStudent.add(students);
arraylistHotel = new ArrayList<Hotel>();
JSONArray jsonArrayHotel = jsonobjectMaps.getJSONArray("hotel");
for (int k = 0; k < jsonArrayHotel.length(); k++) {
jsonobjectMaps = jsonArrayHotel.getJSONObject(k);
Hotel hotel = new Hotel();
hotel.setName(jsonobjectMaps.getString("name"));
arraylistHotel.add(hotel);
}
}
arraylistSearch.add(batches);
batches.setLocation(arraylistStudent);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new CountryAdapter(CountryActivity.this, arraylistSearch);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
}
答案 0 :(得分：2)
以下是代码段，您至少要了解第三级JSON解析的工作原理..
jsonobjectMaps = JSONfunctions.getJSONfromURL("https://dl.dropboxusercontent.com/s/om6509fnyio3165/hotel.json");
try {
JSONArray jsonArraySeaches = jsonobjectMaps.getJSONArray("search");
arraylist = new ArrayList<Search>();
for (int i = 0; i < jsonArraySeaches.length(); i++) {
Search search = new Search();
JSONObject jsonObjectSearch = jsonArraySeaches.getJSONObject(i);
search.setCountry(jsonObjectSearch.getString("country"));
arraylistLocation = new ArrayList<Location>();
JSONArray jsonArrayLocation = jsonObjectSearch.getJSONArray("location");
for (int j = 0; j < jsonArrayLocation.length(); j++) {
JSONObject jsonobjectLocation = jsonArrayLocation.getJSONObject(j);
Location location = new Location();
location.setTitle(jsonobjectLocation.getString("title"));
arraylistHotel= new ArrayList<Hotel>();
JSONArray jsonArrayHotel= jsonobjectLocation.getJSONArray("hotel");
for (int k = 0; k < jsonArrayHotel.length(); k++) {
JSONObject jsonobjectHotel = jsonArrayHotel.getJSONObject(k);
Hotel hotel = new Hotel();
hotel.setName(jsonobjectHotel.getString("name"));
arraylistHotel.add(hotel);
}
location.setHotels(arraylistHotel);
arraylistLocation.add(location);
}
search.setLocations(arraylistLocation);
arraylist.add(search);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
答案 1 :(得分：2)
这是下载JSON数据并将其绑定到listview代码。您可以在此处找到它。
private class DownloadJSON extends AsyncTask<Void, Void, Void> {
private ArrayList<Location> arraylistLocation;
private ArrayList<Hotel> arraylistHotel;
@Override
protected void onPreExecute() {
super.onPreExecute();
mProgressDialog = new ProgressDialog(MainActivity.this);
mProgressDialog.setMessage("Loading...");
mProgressDialog.setIndeterminate(false);
mProgressDialog.show();
}
@Override
protected Void doInBackground(Void... params) {
jsonobjectMaps = JSONfunctions.getJSONfromURL("https://dl.dropboxusercontent.com/s/om6509fnyio3165/hotel.json");
try {
JSONArray jsonArraySeaches = jsonobjectMaps.getJSONArray("search");
arraylist = new ArrayList<Search>();
for (int i = 0; i < jsonArraySeaches.length(); i++) {
Search search = new Search();
JSONObject jsonObjectSearch = jsonArraySeaches.getJSONObject(i);
search.setCountry(jsonObjectSearch.getString("country"));
arraylistLocation = new ArrayList<Location>();
JSONArray jsonArrayLocation = jsonObjectSearch.getJSONArray("location");
for (int j = 0; j < jsonArrayLocation.length(); j++) {
JSONObject jsonobjectLocation = jsonArrayLocation.getJSONObject(j);
Location location = new Location();
location.setTitle(jsonobjectLocation.getString("title"));
arraylistHotel= new ArrayList<Hotel>();
JSONArray jsonArrayHotel= jsonobjectLocation.getJSONArray("hotel");
for (int k = 0; k < jsonArrayHotel.length(); k++) {
JSONObject jsonobjectHotel = jsonArrayHotel.getJSONObject(k);
Hotel hotel = new Hotel();
hotel.setName(jsonobjectHotel.getString("name"));
arraylistHotel.add(hotel);
}
location.setHotels(arraylistHotel);
arraylistLocation.add(location);
}
search.setLocations(arraylistLocation);
arraylist.add(search);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(MainActivity.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// TODO Auto-generated method stub
Bundle bundle = new Bundle();
bundle.putSerializable("data", arraylist);
bundle.putInt("index", position);
Intent sendtosecond = new Intent(MainActivity.this, SecondListActivity.class);
sendtosecond.putExtra("bundle", bundle);
startActivity(sendtosecond);
}
});
}
}
答案 2 :(得分：0)
你在两个地方遇到同样的问题。 ArrayList对象不能直接分配。您需要clone()或使用复制构造函数。
错误在HotelAdapter.java
this.arrayList = arrayList;
你应该做
this.arrayList = arrayList.clone();
arrayList.clear(); //clean up
并在Location.java
public void setHotel(ArrayList<Hotel> hotel) {
this.hotel = hotel.clone();
hotel.clean();
}
或者您可以使用
this.hotel = new ArrayList<Hotel>(hotel);
您的问题是由于this.