java - 网络操作导致 android.os.NetworkOnMainThreadException

Question

我试图编写一个应用程序，它从网站获取一些 JSON，将其转换为数组，然后将该数组的特定元素放入应用程序中表格的不同位置。我编写了获取 JSON 数据并将其转换为 Eclipse 中的 ArrayList 的代码。那里效果很好。我现在尝试在 Android Studio 中实现代码，但无法让它工作。我有以下代码:

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.table_layout);
        TextView textview = (TextView) findViewById(R.id.textView8);
        try{
            textview.setText(MainActivity.get_data().toString());
        }
        catch (Exception e){
            textview.setText(e.getClass().getCanonicalName());
        }
    }

    public static ArrayList<String> get_data() throws Exception{
        String[] ids = new String[] {(here are some ids)};
        ArrayList<String> alldata = new ArrayList<>();
        for(int r=0;r<ids.length;r++) {
            String url = "https://ktrax.kisstech.ch/backend/tracking?db=aviation&sw_lat=40.97765930663377&sw_lon=-26.280096606906117&ne_lat=43.01854550507729&ne_lon=-23.407171802218617&ktrax_id=icao%3a" +ids[r]+"&format=json";
            URL ktraxURL = new URL(url);
            JSONArray test = Networkaccess.getJSONarr(ktraxURL);
            ArrayList<String> listdata = MainActivity.converter(test);
            ArrayList<String> elementlist = new ArrayList<>();
            (some more code (irrelevant in this matter) which makes the array nice and neat)

        //System.out.println(alldata);
        return alldata;
    }

    public static ArrayList<String> converter(JSONArray test){ //creates an array with all the data splited 

    (Some code that converts JSON to ArrayList (also no problems here))
    }
}

class Networkaccess{
    public static JSONArray getJSONarr(URL ktraxURL) throws Exception{
        HttpURLConnection con = (HttpURLConnection) ktraxURL.openConnection();
        //Checking for reponse code of GET Method
        con.setRequestMethod("GET");


!!!!!!     int responseCode = con.getResponseCode(); //THE DEBUGGER JUMPS FROM HERE TO THE CATCH IN MAIN



        System.out.println("Response Code : " +responseCode);
        //Reading Data and
        BufferedReader readin = new BufferedReader(new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();
        while ((inputLine = readin.readLine()) != null) {
            response.append(inputLine);
        }
        readin.close();
        //System.out.println(response.toString());
        String jsonresp = new String(response.toString());
        //System.out.println(jsonresp);
        JSONObject myResponse = new JSONObject(jsonresp);
        JSONArray test = myResponse.getJSONArray("targets");
        //System.out.println(test);
        return test;
    }
}

我创建了新的网络类作为错误，该错误显示在 TextView 字段中:android.os.NetworkOnMainThreadException。然而，这似乎并没有完成这项工作，并且仍然显示相同的错误。我不知道如何从这里继续。调试时，调试器始终运行到我用 !!! 标记的行!在代码中。然后跳转到主activity中的catch异常处。

期待您的答复!

Answer 1

网络内容往往会堵塞，因为响应可能需要一段时间才能传递。它的意思是，您需要将代码移至另一个线程，以便您的程序在等待响应时不会卡住。

这不会阻止与网络相关的速度下降，但会消除错误:

Thread networking = new Thread(){
    void run() {
        int responseCode = con.getResponseCode();
    }
}
networking.start();
networking.join();