9Roms: Scan Reachable IP to discover devices in network

This example, scan a range of IPs, to check if it is reachable, in turn to discover connected devices in the same network.

MainActivity.java

package com.blogspot.android_er.androidipscanner;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    private Button btnScan;
    private ListView listViewIp;

    ArrayList<String> ipList;
    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnScan = (Button)findViewById(R.id.scan);
        listViewIp = (ListView)findViewById(R.id.listviewip);


        ipList = new ArrayList();
        adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, android.R.id.text1, ipList);
        listViewIp.setAdapter(adapter);

        btnScan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new ScanIpTask().execute();
            }
        });

    }

    private class ScanIpTask extends AsyncTask<Void, String, Void>{

        /*
        Scan IP 192.168.1.100~192.168.1.110
        you should try different timeout for your network/devices
         */
        static final String subnet = "192.168.1.";
        static final int lower = 100;
        static final int upper = 110;
        static final int timeout = 5000;

        @Override
        protected void onPreExecute() {
            ipList.clear();
            adapter.notifyDataSetInvalidated();
            Toast.makeText(MainActivity.this, "Scan IP...", Toast.LENGTH_LONG).show();
        }

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

            for (int i = lower; i <= upper; i++) {
                String host = subnet + i;

                try {
                    InetAddress inetAddress = InetAddress.getByName(host);
                    if (inetAddress.isReachable(timeout)){
                        publishProgress(inetAddress.toString());
                    }

                } catch (UnknownHostException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            return null;
        }

        @Override
        protected void onProgressUpdate(String... values) {
            ipList.add(values[0]);
            adapter.notifyDataSetInvalidated();
            Toast.makeText(MainActivity.this, values[0], Toast.LENGTH_LONG).show();
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            Toast.makeText(MainActivity.this, "Done", Toast.LENGTH_LONG).show();
        }
    }

}

layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />

    <Button
        android:id="@+id/scan"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Scan"/>
    <ListView
        android:id="@+id/listviewip"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

Permission of "android.permission.INTERNET" is needed in AndroidManifest.xml

    <uses-permission android:name="android.permission.INTERNET"/>