Scan Devices IP connected in WiFi network

Example to scan connected devices within the same WiFi network, using InetAddress.isReachable().

package com.blogspot.android_er.androidwireless;

import android.content.Context;
import android.net.wifi.WifiManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;

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

public class MainActivity extends AppCompatActivity {

TextView tvWifiState;
TextView tvScanning, tvResult;

ArrayList<InetAddress> inetAddresses;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

tvWifiState = (TextView)findViewById(R.id.WifiState);
tvScanning = (TextView)findViewById(R.id.Scanning);
tvResult = (TextView)findViewById(R.id.Result);

//To prevent memory leaks on devices prior to Android N,
//retrieve WifiManager with
//getApplicationContext().getSystemService(Context.WIFI_SERVICE),
//instead of getSystemService(Context.WIFI_SERVICE)
WifiManager wifiManager =
(WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
tvWifiState.setText(readtvWifiState(wifiManager));

new ScanTask(tvScanning, tvResult).execute();
}

// "android.permission.ACCESS_WIFI_STATE" is needed
private String readtvWifiState(WifiManager wm){
String result = "";
switch (wm.getWifiState()){
case WifiManager.WIFI_STATE_DISABLED:
result = "WIFI_STATE_DISABLED";
break;
case WifiManager.WIFI_STATE_DISABLING:
result = "WIFI_STATE_DISABLING";
break;
case WifiManager.WIFI_STATE_ENABLED:
result = "WIFI_STATE_ENABLED";
break;
case WifiManager.WIFI_STATE_ENABLING:
result = "WIFI_STATE_ENABLING";
break;
case WifiManager.WIFI_STATE_UNKNOWN:
result = "WIFI_STATE_UNKNOWN";
break;
default:
}
return result;
}

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

TextView tvCurrentScanning, tvScanResullt;
ArrayList<String> canonicalHostNames;

public ScanTask(TextView tvCurrentScanning, TextView tvScanResullt) {
this.tvCurrentScanning = tvCurrentScanning;
this.tvScanResullt = tvScanResullt;
}

@Override
protected void onPostExecute(Void aVoid) {
tvCurrentScanning.setText("Finished.");
tvScanResullt.setText("");
for(int i = 0; i < inetAddresses.size(); i++){
tvScanResullt.append(canonicalHostNames.get(i) + "\n");
}
}

@Override
protected Void doInBackground(Void... voids) {
scanInetAddresses();
return null;
}

@Override
protected void onProgressUpdate(String... values) {
tvCurrentScanning.setText(values[0]);
}

private void scanInetAddresses(){
//May be you have to adjust the timeout
final int timeout = 500;

if(inetAddresses == null){
inetAddresses = new ArrayList<>();
}
inetAddresses.clear();

if(canonicalHostNames == null){
canonicalHostNames = new ArrayList<>();
}
canonicalHostNames.clear();

//For demonstration, scan 192.168.1.xxx only
byte[] ip = {(byte) 192, (byte) 168, (byte) 1, 0};
for (int j = 0; j < 255; j++) {
ip[3] = (byte) j;
try {
InetAddress checkAddress = InetAddress.getByAddress(ip);
publishProgress(checkAddress.getCanonicalHostName());
if (checkAddress.isReachable(timeout)) {
inetAddresses.add(checkAddress);
canonicalHostNames.add(checkAddress.getCanonicalHostName());
}
} catch (UnknownHostException e) {
e.printStackTrace();
publishProgress(e.getMessage());
} catch (IOException e) {
e.printStackTrace();
publishProgress(e.getMessage());
}
}
}
}
}

<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:orientation="vertical"
tools:context="com.blogspot.android_er.androidwireless.MainActivity" >

<TextView
android:id="@+id/title"
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" />

<TextView
android:id="@+id/WifiState"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Scanning: "/>
<TextView
android:id="@+id/Scanning"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textStyle="italic"/>
</LinearLayout>

<TextView
android:id="@+id/Result"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textStyle="bold"/>

</LinearLayout>

uses-permission of “android.permission.ACCESS_WIFI_STATE” and “android.permission.INTERNET” are needed.

Android-er