KotlinでAndroidのWi-Fi情報を取得する

以下はMainActivity.ktの様子です。

package com.wifiexample.example

import android.Manifest
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.content.pm.PackageManager
import android.net.wifi.WifiManager
import android.os.Build
import android.os.Bundle
import android.widget.TextView
import androidx.annotation.RequiresApi
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    private val wifiManager: WifiManager get() = this.applicationContext.getSystemService(Context.WIFI_SERVICE) as WifiManager
    private val PERMISSIONS_REQUEST_CODE = 1

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED ||
                checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED ||
                checkSelfPermission(Manifest.permission.ACCESS_WIFI_STATE) != PackageManager.PERMISSION_GRANTED ||
                checkSelfPermission(Manifest.permission.ACCESS_NETWORK_STATE) != PackageManager.PERMISSION_GRANTED
                    ) {
                requestPermissions(
                    arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION,
                        Manifest.permission.ACCESS_FINE_LOCATION,
                        Manifest.permission.ACCESS_WIFI_STATE,
                        Manifest.permission.ACCESS_NETWORK_STATE),
                    PERMISSIONS_REQUEST_CODE);
            }
        }

        val intentFilter = IntentFilter()
        intentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)
        this.registerReceiver(wifiScanReceiver, intentFilter)
        if (wifiManager.wifiState == WifiManager.WIFI_STATE_ENABLED) {
            val results = wifiManager.scanResults
            println(results)
        }
    }

    val wifiScanReceiver = object : BroadcastReceiver() {
        @RequiresApi(Build.VERSION_CODES.M)
        override fun onReceive(context: Context, intent: Intent) {
            val success = intent.getBooleanExtra(WifiManager.EXTRA_RESULTS_UPDATED, false)
            if (success) {
                scanSuccess()
            } else {
                scanFailure()
            }
        }
    }

    private fun scanSuccess() {
        val results = wifiManager.scanResults
        println(results)
    }

    private fun scanFailure() {
        val results = wifiManager.scanResults
        println(results)
    }
}

パーミッション許可周りが肝心な部分です。

AndroidManifest.xmlのpermissionは以下のようになります。

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

SSIDが<unknown ssid>になる

恐らく何かの権限が足りていません。AndroidManifest.xmlの権限周りを確認しましょう。

resultsが空

スマホの本体でWiFi周りの設定をオンにしましょう。

参考

Wi-Fi スキャンの概要(公式)