read from remote text file

[Mohsen Dehghani]

hi .. i need a code to read a text file from an online source and display the content it in a TextView. the code should be placed in the onCreate method of the main activity of an android project. i tried a few codes but no result.

[Stephan van Hulst]

So show us what you tried and what you're stuck on.

[Mohsen Dehghani]

Stephan van Hulst wrote:So show us what you tried and what you're stuck on.

this is what i've tried :

import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebView;
import android.widget.TextView;

import com.google.android.gms.analytics.HitBuilders;
import com.google.android.gms.analytics.Tracker;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Calendar;

public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        final ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        final NetworkInfo activeNetwork = conMgr.getActiveNetworkInfo();
        if (activeNetwork != null && activeNetwork.isConnected() )
        {


            try {
                // Create a URL for the desired page
                URL url = new URL("http://dadhesab.ir/appversion.txt");

                // Read all the text returned by the server
                BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                String str = in.readLine();
                in.close();
                
                TextView tv = (TextView) findViewById(R.id.updateNotice);
                tv.setText(str);
            }
            catch (MalformedURLException e) {
            }
            catch (IOException e) {
            }

        }

    }

but the app crashes on start and the error refers to this line:

     BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

[Darryl A. J. Staflund]

Hi there,

You can do this as follows:

1. Place your text file in '/res/raw' to indicate that this file contains raw data.
2. Then read in a manner similar to the following:

    @OnCreate
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        processFile(R.raw.fileName);
        ...
    }


    /**
     * Given a database and resource id to an SQL script, applies the script to the database.
     *
     * @param db to apply script to
     * @param rawResourceId of script to apply to database
     */
    private void processFile(int rawResourceId){
        final InputStream is = mContext.getResources().openRawResource(rawResourceId);
        final StringBuilder queries = new StringBuilder();

        try {
            final Reader isr = new InputStreamReader(is);
            final BufferedReader br = new BufferedReader(isr);

            String line;
            while ((line = br.readLine()) != null) {
                queries.append(line);
            }
        }

        catch (final IOException e) {
            Log.e(sLogTag, "IO Exception encountered.", e);
        }

        // DO SOMETHING WITH RESULTS HERE
    }

Customize as needed.

Hope this helps.
Darryl

[Mohsen Dehghani]

Darryl A. J. Staflund wrote:Hi there,

You can do this as follows:

1. Place your text file in '/res/raw' to indicate that this file contains raw data.
2. Then read in a manner similar to the following:

the file should be read from a URL because it gets updated from time to time.

[Ron McLeod]

Mohsen Dehghani wrote:the app crashes on start and the error refers to this line:

     BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

It looks like you are trying to do network operations on the main (UI) thread. Use LogCat - you should see something like: android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork). For debugging, you can temporarily change the thread policy to allow network operations, but the real fix is to move this off to another thread.

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
	.permitNetwork().build());

BufferedReader in = new BufferedReader(
	new InputStreamReader(url.openStream()));

[Mohsen Dehghani]

Ron McLeod wrote:
For debugging, you can temporarily change the thread policy to allow network operations, but the real fix is to move this off to another thread.

thanks for your precious advice. the app is working now but do you mean that i shouldn't publish it as is? if so, how can i "move this off to another thread"?

[Ron McLeod]

The concern is that if your network operation takes some time (due to server overload, poor network connectivity, etc.), that your UI will become unresponsive and appear to be frozen.

The most common way to offload to another thread would be to extend the AsyncTask helper class. Do your work in the doInBackground method, and process the retrieved data in the onPostExecute method. If you are gonig to update the UI from the worker thread, you will need to use something like runOnUiThread.

Correction: AsyncTask takes care of running the onPostCreate method in the main/UI thread for you - so no need to so anything special.

[Mohsen Dehghani]

Ron McLeod wrote:
Correction: AsyncTask takes care of running the onPostCreate method in the main/UI thread for you - so no need to so anything special.

thanks a lot for your edit!
I've tried to make an asynctask to handle the desired operation and added it to the MainActivity but i guess it's a bit complicated for me. can you trim it in a way that makes sense?? and how can i call it in the onCreate block?

    private class readtexttask extends AsyncTask<String, Integer, Long> {
        protected Long doInBackground(String... urls) {
            try {
                // Create a URL for the desired page
                URL url = new URL("http://dadhesab.ir/appversion.txt");

                // Read all the text returned by the server
                BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                String str = in.readLine();
                in.close();


            }
            catch (MalformedURLException e) {
            }
            catch (IOException e) {
            }
            return ?;

        }


        protected void onProgressUpdate(Integer... progress) {
        }

        protected void onPostExecute(Long result) {
            TextView tv = (TextView) findViewById(R.id.updateNotice);
            tv.setText(str);
        }
    }

[Ron McLeod]

You are pretty close - just clean-up a few things and you'll be done.

Remove the URL from the ReadTextTask class and pass it in as an argument in case you want this to be configurable or come from a database later-on. Also, to keep things simple (for now), it might be better just to return the value from the server as a String, especially if all you are going to do with it is display it in the UI. Finally, since you aren't using onProgressUpdate, just remove it.

That would leave you with:

private class ReadTextTask extends AsyncTask<URL, Void, String> {
	@Override
    protected String doInBackground(URL... urls) {
        try {
            // Read all the text returned by the server
            BufferedReader in = new BufferedReader(new InputStreamReader(urls[0].openStream()));
            String str = in.readLine();
            in.close();
        }
        catch (IOException e) {
            // ** do something here **
        }
        return str;
    }
 
	@Override
    protected void onPostExecute(String result) {
        TextView tv = (TextView) findViewById(R.id.updateNotice);
        tv.setText(str);
    }
}

Now to call it form your onCreate method, use your existing code to create the URL, create a new instance of your class, and then execute it with the URL as the argument.

try {
	// Create a URL for the desired page
	URL url = new URL("http://dadhesab.ir/appversion.txt");
	
	// launch task
	new ReadTextTask().execute(url);
}
catch (MalformedURLException e) {
    // ** do something here **
}

[Mohsen Dehghani]

Ron McLeod wrote:You are pretty close - just clean-up a few things and you'll be done.

thanks a lot! it seems to work fine unless it appears to return an empty string! this is my code so far:

import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebView;
import android.widget.TextView;

import com.google.android.gms.analytics.HitBuilders;
import com.google.android.gms.analytics.Tracker;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Calendar;

public class MainActivity extends AppCompatActivity {
    private Tracker mTracker;
    private String str ="";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        final ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        final NetworkInfo activeNetwork = conMgr.getActiveNetworkInfo();
        if (activeNetwork != null && activeNetwork.isConnected() )
        {

            try {
                // Create a URL for the desired page
                URL url = new URL("http://dadhesab.ir/appversion.txt");

                // launch task
                new ReadTextTask().execute(url);
            }
            catch (MalformedURLException e) {
                // ** do something here **
            }


        }
        else
        {

        }

    }

    private class ReadTextTask extends AsyncTask<URL, Void, String> {
        @Override
        protected String doInBackground(URL... urls) {
            try {
                // Read all the text returned by the server
                BufferedReader in = new BufferedReader(new InputStreamReader(urls[0].openStream()));
                String str = in.readLine();
                in.close();
            }
            catch (IOException e) {
                // ** do something here **
            }
            return str;
        }

        @Override
        protected void onPostExecute(String result) {
            TextView tv = (TextView) findViewById(R.id.updateNotice);
            tv.setText(str);
        }
    }

    . . .


 
}

[Ron McLeod]

The problem is that the UI is being updated with the value of the instance variable (empty String) rather than what was read from the server.

Delete the line with private String str =""; at the top of your MainActivity class, and add String str = null; before the try block in your ReadTextTask class.

[Mohsen Dehghani]

Ron McLeod wrote:The problem is that the UI is being updated with the value of the instance variable (empty String) rather than what was read from the server.

Delete the line with private String str =""; at the top of your MainActivity class, and add String str = null; before the try block in your ReadTextTask class.

thanks a lot. works like charm

[Dave Tolls]

I take it this file only has the one line in it.

[Mohsen Dehghani]

Dave Tolls wrote:I take it this file only has the one line in it.

only a number