Question

我只是一个初学者，从网上学习Json解析和流，好吧，我没有在这个应用程序中得到错误，但它没有显示任何东西。我不知道问题是什么，并且无法在日志中看到任何问题。这是代码：

    InputStream is;
String line;
TextView textView;




@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView) findViewById(R.id.text);
    try {
        URL url = new URL("https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&minlatitude=4&maxlatitude=5");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        is = new BufferedInputStream(connection.getInputStream());
        if(connection.getInputStream()==null)
        {
            textView.setText("input stream empty");
        }
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));

        StringBuilder builder = new StringBuilder();

        while((line=reader.readLine())!=null){
            builder.append(line);
        }
        if(builder.toString().equals(""))
        {
            textView.setText("no work builder empty");
        }

        line=builder.toString();
        JSONObject object = new JSONObject(line);
        JSONArray fea = object.getJSONArray("features");
        JSONObject QUAKE = fea.getJSONObject(0);
        JSONObject pro = QUAKE.getJSONObject("properties");
        int mag = pro.getInt("mag");
        textView.setText(mag+"");



    } catch (Exception e) {
        e.printStackTrace();
    }


}

谢谢！

Answer 1

在主线程上进行任何网络操作都是Android中的犯罪行为。您将受到network_operation_on_main_thread异常的惩罚。您需要从AsyncTask获取帮助。

请尝试以下代码

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
new LongOperation().execute("");
}


private class LongOperation extends AsyncTask<String, Void, String> {
   String data = "input stream empty";
    @Override
    protected String doInBackground(String... params) {
        try {
    URL url = new URL("https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&minlatitude=4&maxlatitude=5");
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    is = new BufferedInputStream(connection.getInputStream());

    BufferedReader reader = new BufferedReader(new InputStreamReader(is));

    StringBuilder builder = new StringBuilder();

    while((line=reader.readLine())!=null){
        builder.append(line);
    }
    if(builder.toString().equals(""))
    {
        data = "no work builder empty";
    }

    line=builder.toString();
    JSONObject object = new JSONObject(line);
    JSONArray fea = object.getJSONArray("features");
    JSONObject QUAKE = fea.getJSONObject(0);
    JSONObject pro = QUAKE.getJSONObject("properties");
    int mag = pro.getInt("mag");
    data = mag+"";



} catch (Exception e) {
    e.printStackTrace();
}
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
     textView.setText(data);
    }

    @Override
    protected void onPreExecute() {

    }

    @Override
    protected void onProgressUpdate(Void... values) {
    }
}

Answer 2

当应用程序尝试在其主线程上执行网络操作时，抛出异常。因此，当您在主线程上进行网络调用时，网络调用将不会发生，并且它将直接抛出 NetworkOnMainThreadException 而不是进行网络调用。在 AsyncTask

中运行您的代码

无法在应用程序上获取Json信息

2 个答案: