java Android JSON对象正在返回null

1 年，2 月 Questions & Answers 701

我看了这里的其他帖子，还没有找到问题的答案。我正在Android中练习JSON，为此我使用了forecast。io API。下面是JSON的样子：https://api.forecast.io/forecast/7d5566f0ebf0fe263426f12b52d5c51c/37.8267,-122.423

我从这里的另一篇帖子中获得了代码，可以帮助我开始：

    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）包装初始化时，代码才会运行，所以我猜不会检索到JSON。我可能做错了什么

编辑：这是stacktrace

 01-21 15:28:42.857: W/System.err(31328):安卓.os.NetworkOnMainThreadException
01-21 15:28:42.857: W/System.err(31328):at 安卓.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    安卓.app.Activity.performCreate(Activity.java:5231)

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java Android JSON对象正在返回null

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