[英]Android java JSON parsing 'null' as output
We have been using this code in our application to fetch data from an online database, but whatever we tried, it keeps saying "null" as an output by album and duration. 我们一直在我们的应用程序中使用此代码从在线数据库中获取数据,但无论我们尝试过什么,它都会按照专辑和持续时间将“null”作为输出。 It could be a very small detail, but since we are beginning developers, we don't really know a lot about JSON. 它可能是一个非常小的细节,但由于我们是开始开发人员,我们对JSON并不是很了解。 Has anyone got any suggestions? 有没有人有任何建议?
package com.example.androidhive;
import java.util.ArrayList;
import java.util.List;
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.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.Html;
import android.util.Log;
import android.widget.TextView;
import com.example.androidhive.helper.AlertDialogManager;
import com.example.androidhive.helper.ConnectionDetector;
import com.example.androidhive.helper.JSONParser;
public class SingleTrackActivity extends Activity {
// Connection detector
ConnectionDetector cd;
// Alert dialog manager
AlertDialogManager alert = new AlertDialogManager();
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jsonParser = new JSONParser();
// tracks JSONArray
JSONArray albums = null;
// Album id
String album_id = null;
String song_id = null;
String album_name, song_name, duration;
// single song JSON url
// GET parameters album, song
private static final String URL_SONG = "http://api.androidhive.info/songs/track.php";
// ALL JSON node names
private static final String TAG_NAME = "name";
private static final String TAG_DURATION = "duration";
private static final String TAG_ALBUM = "album";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_single_track);
cd = new ConnectionDetector(getApplicationContext());
// Check if Internet present
if (!cd.isConnectingToInternet()) {
// Internet Connection is not present
alert.showAlertDialog(SingleTrackActivity.this, "Internet Connection Error",
"Please connect to working Internet connection", false);
// stop executing code by return
return;
}
// Get album id, song id
Intent i = getIntent();
album_id = i.getStringExtra("album_id");
song_id = i.getStringExtra("song_id");
// calling background thread
new LoadSingleTrack().execute();
}
/**
* Background Async Task to get single song information
* */
class LoadSingleTrack extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(SingleTrackActivity.this);
pDialog.setMessage("Loading song ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting song json and parsing
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// post album id, song id as GET parameters
params.add(new BasicNameValuePair("album", album_id));
params.add(new BasicNameValuePair("song", song_id));
// getting JSON string from URL
String json = jsonParser.makeHttpRequest(URL_SONG, "GET",
params);
// Check your log cat for JSON reponse
Log.d("Single Track JSON: ", json);
try {
JSONObject jObj = new JSONObject(json);
if(jObj != null){
song_name = jObj.getString(TAG_NAME);
album_name = jObj.getString(TAG_ALBUM);
duration = jObj.getString(TAG_DURATION);
}
} 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 song information
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
TextView txt_song_name = (TextView) findViewById(R.id.song_title);
TextView txt_album_name = (TextView) findViewById(R.id.album_name);
TextView txt_duration = (TextView) findViewById(R.id.duration);
// displaying song data in view
txt_song_name.setText(song_name);
txt_album_name.setText(Html.fromHtml("<b>Album:</b> " + album_name));
txt_duration.setText(Html.fromHtml("<b>Duration:</b> " + duration));
// Change Activity Title with Song title
setTitle(song_name);
}
});
}
}
}
Looking at the tutorial you link to, it appears this is what a request would look like: 查看链接到的教程,看起来这就是请求的样子:
http://api.androidhive.info/songs/track.php?album=3&song=1
and the response is: 并且响应是:
{"id":1,"name":"Born to Die","duration":"4:46","album_id":"3","album":"Lana Del Rey - Born to Die"}
Given that ... there's nothing wrong with your JSON parsing. 鉴于......你的JSON解析没有任何问题。
You need to verify the "album" ( album_id
) and "song" ( song_id
) parameters are what you think they are when you do your GET
. 您需要验证“专辑”( album_id
)和“歌曲”( song_id
)参数是您在进行GET
时的认为。
The PHP script doesn't return any data if they are empty (eg http://api.androidhive.info/songs/track.php?album=&song=
) and simply returns no album
if they aren't something it recognizes. 如果PHP脚本为空(例如http://api.androidhive.info/songs/track.php?album=&song=
),则不返回任何数据,如果它们不是它识别的内容,则不返回no album
。 It would appear that's what is occurring and therefore the output of your program is null
for the values. 它似乎正在发生的事情,因此程序的输出对于值为null
。
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