我正在编写一个应用程序，在该应用程序中我从 JSON 获取数据，并且我能够获取类别列表，但是每当我单击任何类别时，没有获得该特定类别下的产品列表总是得到空白活动。
JSON：
[
{
"categoryId": "1",
"categoryTitle": "SmartPhones", "SmartPhones": [
{
"itemId": "1",
"itemTitle": "Galaxy Mega 5.8"
},
{
"itemId": "2",
"itemTitle": "Galaxy Mega 6.3"
}
]
},
{
"categoryId": "2",
"categoryTitle": "Tablets", "Tablets": [
{
"itemId": "1",
"itemTitle": "Galaxy Note 510"
},
{
"itemId": "2",
"itemTitle": "Galaxy Note 800"
}
]
}
]
AlbumsActivity.java [用于类别]：
public class AlbumsActivity extends ListActivity {
// Connection detector
ConnectionDetector cd;
// Alert dialog manager
AlertDialogManager alert = new AlertDialogManager();
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jsonParser = new JSONParser();
ArrayList<HashMap<String, String>> albumsList;
// albums JSONArray
JSONArray albums = null;
// albums JSON url
private static final String URL_ALBUMS = "my.json"; //providing proper URL
// ALL JSON node names
private static final String TAG_ID = "categoryId";
private static final String TAG_NAME = "categoryTitle";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_albums);
cd = new ConnectionDetector(getApplicationContext());
// Check for internet connection
if (!cd.isConnectingToInternet()) {
// Internet Connection is not present
alert.showAlertDialog(AlbumsActivity.this, "Internet Connection Error",
"Please connect to working Internet connection", false);
// stop executing code by return
return;
}
// Hashmap for ListView
albumsList = new ArrayList<HashMap<String, String>>();
// Loading Albums JSON in Background Thread
new LoadAlbums().execute();
// get listview
ListView lv = getListView();
/**
* Listview item click listener
* TrackListActivity will be lauched by passing album id
* */
lv.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View view, int arg2,
long arg3) {
// on selecting a single album
// TrackListActivity will be launched to show tracks inside the album
Intent i = new Intent(getApplicationContext(), TrackListActivity.class);
// send album id to tracklist activity to get list of songs under that album
String album_id = ((TextView) view.findViewById(R.id.album_id)).getText().toString();
i.putExtra("album_id", album_id);
startActivity(i);
}
});
}
/**
* Background Async Task to Load all Albums by making http request
* */
class LoadAlbums extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(AlbumsActivity.this);
pDialog.setMessage("Listing Albums ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting Albums JSON
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
String json = jsonParser.makeHttpRequest(URL_ALBUMS, "GET",
params);
// Check your log cat for JSON reponse
Log.d("Albums JSON: ", "> " + json);
try {
albums = new JSONArray(json);
if (albums != null) {
// looping through All albums
for (int i = 0; i < albums.length(); i++) {
JSONObject c = albums.getJSONObject(i);
// Storing each json item values in variable
String id = c.getString(TAG_ID);
String name = c.getString(TAG_NAME);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ID, id);
map.put(TAG_NAME, name);
// adding HashList to ArrayList
albumsList.add(map);
}
}else{
Log.d("Albums: ", "null");
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all albums
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
AlbumsActivity.this, albumsList,
R.layout.list_item_albums, new String[] { TAG_ID,
TAG_NAME }, new int[] {
R.id.album_id, R.id.album_name });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
TrackListActivity.java [用于产品]：
public class TrackListActivity extends ListActivity {
// Connection detector
ConnectionDetector cd;
// Alert dialog manager
AlertDialogManager alert = new AlertDialogManager();
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jsonParser = new JSONParser();
ArrayList<HashMap<String, String>> tracksList;
// tracks JSONArray
JSONArray albums = null;
// Album id
String album_id, album_name;
// tracks JSON url
// id - should be posted as GET params to get track list (ex: id = 5)
private static final String URL_ALBUMS = "my.json"; //providing proper url
// ALL JSON node names
private static final String TAG_ID = "itemId";
private static final String TAG_NAME = "itemTitle";
private static final String TAG_ALBUM = "categoryId";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tracks);
cd = new ConnectionDetector(getApplicationContext());
// Check if Internet present
if (!cd.isConnectingToInternet()) {
// Internet Connection is not present
alert.showAlertDialog(TrackListActivity.this, "Internet Connection Error",
"Please connect to working Internet connection", false);
// stop executing code by return
return;
}
// Get album id
Intent i = getIntent();
album_id = i.getStringExtra("album_id");
// Hashmap for ListView
tracksList = new ArrayList<HashMap<String, String>>();
// Loading tracks in Background Thread
new LoadTracks().execute();
// get listview
ListView lv = getListView();
/**
* Listview on item click listener
* SingleTrackActivity will be lauched by passing album id, song id
* */
lv.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View view, int arg2,
long arg3) {
// On selecting single track get song information
Intent i = new Intent(getApplicationContext(), SingleTrackActivity.class);
// to get song information
// both album id and song is needed
String album_id = ((TextView) view.findViewById(R.id.album_id)).getText().toString();
String song_id = ((TextView) view.findViewById(R.id.song_id)).getText().toString();
Toast.makeText(getApplicationContext(), "Album Id: " + album_id + ", Song Id: " + song_id, Toast.LENGTH_SHORT).show();
i.putExtra("album_id", album_id);
i.putExtra("song_id", song_id);
startActivity(i);
}
});
}
/**
* Background Async Task to Load all tracks under one album
* */
class LoadTracks extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(TrackListActivity.this);
pDialog.setMessage("Loading songs ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting tracks json and parsing
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// post album id as GET parameter
params.add(new BasicNameValuePair(TAG_ID, album_id));
// getting JSON string from URL
String json = jsonParser.makeHttpRequest(URL_ALBUMS, "GET",
params);
// Check your log cat for JSON reponse
Log.d("Track List JSON: ", json);
try {
JSONObject jObj = new JSONObject(json);
if (jObj != null) {
String album_id = jObj.getString(TAG_ID);
album_name = jObj.getString(TAG_ALBUM);
if (albums != null) {
// looping through All songs
for (int i = 0; i < albums.length(); i++) {
JSONObject c = albums.getJSONObject(i);
// Storing each json item in variable
String song_id = c.getString(TAG_ID);
String name = c.getString(TAG_NAME);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put("album_id", album_id);
map.put(TAG_ID, song_id);
map.put(TAG_NAME, name);
// adding HashList to ArrayList
tracksList.add(map);
}
} else {
Log.d("Albums: ", "null");
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all tracks
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
TrackListActivity.this, tracksList,
R.layout.list_item_tracks, new String[] { "album_id", TAG_ID,
TAG_NAME }, new int[] {
R.id.album_id, R.id.song_id, R.id.album_name });
// updating listview
setListAdapter(adapter);
// Change Activity Title with Album name
setTitle(album_name);
}
});
}
}
}