Android - define "context" in AsyncTask

Issue

I'm a newbie in Android application programming (even in Java). I have my own data from my weather stations and I decode them in background from JSON - that all wokrs fine.

in the "onPostExecute" function I call another function called "save". And in this function i need "context".

How do I define this "context"? or where should I take it from? Can you please direct me in my example?

I tried some google variants, but each time the application stops working. (Android 5.1 - Lenovo P70) - I can not use a virtual device on my computer, so Iam testing my app directly on my phone after connecting with Android studio.

I will be grateful for any advice.

Here is "fetchData.java" which contains a function "fetchData" which is called from "MainActivity.java" when i touch a button.

package arduino.weatherstation;

import android.content.Context;
import android.os.AsyncTask;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;



public class fetchData extends AsyncTask<String,String,String> {
    String data = "";
    private String dataParsed = "";
    private String singleParsed = "";
    private String last_data = "";
    private static final String FILE_NAME = "lastdata.txt";

    @Override
    protected String doInBackground(String... params) {

        String result = "";

        try {
            URL url = new URL("https://***.cz");

            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while(line != null) {
                line = bufferedReader.readLine();
                data = data + line;
            }


            JSONArray JA = new JSONArray(data);
            for(int i = 0; i < JA.length(); i++) {
                JSONObject JO = (JSONObject) JA.get(i);
                singleParsed =  "Day:" + JO.get("Day") + "\n"+
                                "Time:" + JO.get("Time") + "\n"+
                                "Temperature:" + JO.get("Temperature") + "\n"+
                                "Humidity:" + JO.get("Humidity") + "\n"+
                                "Pressure:" + JO.get("Pressure") + "\n"+
                                "Light:" + JO.get("Light") + "\n"+
                                "Rain:" + JO.get("Rain") + "\n"+
                                "City:" + JO.get("City") + "\n"+
                                "Country:" + JO.get("Country") + "\n"+
                                "Id:" + JO.get("Id") + "\n";
                dataParsed = dataParsed + singleParsed;
                if(i == (JA.length() - 1)) {
                    last_data = "Day:" + JO.get("Day") + "\n"+
                            "Time:" + JO.get("Time") + "\n"+
                            "Temperature:" + JO.get("Temperature") + "\n"+
                            "Humidity:" + JO.get("Humidity") + "\n"+
                            "Pressure:" + JO.get("Pressure") + "\n"+
                            "Light:" + JO.get("Light") + "\n"+
                            "Rain:" + JO.get("Rain") + "\n"+
                            "City:" + JO.get("City") + "\n"+
                            "Country:" + JO.get("Country") + "\n"+
                            "Id:" + JO.get("Id") + "\n";
                }
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }


        return result;
    }

    @Override
    protected void onPostExecute(String aVoid) {
        super.onPostExecute(aVoid);
        MainActivity.data.setText(last_data);       

        save(last_data);
    }

    public void save(String toSave) {
        String text = toSave;
        FileOutputStream fos = null;

        try {
            fos = context.openFileOutput(FILE_NAME, Context.MODE_PRIVATE);
            fos.write(text.getBytes());

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

Solution

First declare a Context variable in your fetchData class like this

Context context;

Now make a constructor for fetchData and take context as an argument like this

public fetchData(Context context)
{
    this.context = context;
}

Then wherever you are creating an object of fetchData pass the context form that class like

fetchData fetchObject = new fetchData(this);
fetchObject.execute();

When you are using context for file it will be available in your fetchData class context variable. Hope it helps.

Answered By - AIK