Question

我看过这里的其他帖子，但我找不到问题的答案。我正在Android中练习JSON，我正在使用forecast.io API。这是JSON的样子：https://api.forecast.io/forecast/7d5566f0ebf0fe263426f12b52d5c51c/37.8267,-122.423。

我得到的代码可以帮助我从另一篇帖子开始：

    LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
    Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    double LONGITUDE = location.getLongitude();
    double LATITUDE = location.getLatitude();

    DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
    HttpPost httppost = new HttpPost("https://api.forecast.io/forecast/7d5566f0ebf0fe263426f12b52d5c51c/" + LATITUDE + "," + LONGITUDE);
    // Depends on your web service
    httppost.setHeader("Content-type", "application/json");

    InputStream inputStream = null;
    String result = null;
    try {
        HttpResponse response = httpclient.execute(httppost);           
        HttpEntity entity = response.getEntity();

        inputStream = entity.getContent();
        // json is UTF-8 by default
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
        StringBuilder sb = new StringBuilder();

        String line = null;
        while ((line = reader.readLine()) != null)
        {
            sb.append(line + "\n");
        }
        result = sb.toString();


    } catch (Exception e) { 
        // Oops
    }
    finally {
        try{if(inputStream != null)inputStream.close();}catch(Exception squish){}
    }




    try {
        JSONObject j = new JSONObject(result);
        String timezone = j.getString("timezone");
        text.setText(timezone + "");

    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

这一行给了我一个错误：

JSONObject j = new JSONObject(result);

它给出了一个空指针异常。只有当我用if（result！= null）包装initializatin时，代码才会运行所以我想没有检索到JSON。我能做错什么？

编辑：这是堆栈跟踪

 01-21 15:28:42.857: W/System.err(31328):android.os.NetworkOnMainThreadException
01-21 15:28:42.857: W/System.err(31328):at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
01-21 15:28:42.857: W/System.err(31328):at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
01-21 15:28:42.857: W/System.err(31328):at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
01-21 15:28:42.857: W/System.err(31328):at java.net.InetAddress.getAllByName(InetAddress.java:214)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
01-21 15:28:42.857: W/System.err(31328):at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
01-21 15:28:42.857: W/System.err(31328):at com.example.weatherapp.MainActivity.onCreate(MainActivity.java:48)
01-21 15:28:42.857: W/System.err(31328):at    android.app.Activity.performCreate(Activity.java:5231)

Answer 1

这是因为，正如异常所述，您正试图在主线程上访问互联网。 Android不允许这样做，因为它可能会滞后于UI。因此，您需要在不是UI线程的单独线程上连接到Internet。请参阅http://developer.android.com/reference/android/os/AsyncTask.html（您只需要doInBackground进行互联网访问）。

Answer 2

当您将代码移动到（例如）AsyncTask中时，请从您的网址中删除“s”。它应该是http而不是https，否则你将获得404而没有数据。

Android JSON对象返回null

2 个答案: