• NetWork Connected 검사 함수

private fun isNetworkConnected(): Boolean {
    val connectivityManager = getSystemService(ConnectivityManager::class.java)
    val currentNetwork = connectivityManager.activeNetwork
    val caps = connectivityManager.getNetworkCapabilities(currentNetwork) ?: return false 
    
    return when {
        caps.hasTransport(NetworkCapabilities.TRANSPORT_WIFI) -> true
        caps.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR) -> true
        caps.hasTransport(NetworkCapabilities.TRANSPORT_ETHERNET) -> true
        else -> false
    }
}

• NetWork 검사 콜백 메소드

val connectivityManager = getSystemService(ConnectivityManager::class.java)

connectivityManager.registerDefaultNetworkCallback(object : ConnectivityManager.NetworkCallback() {
    override fun onAvailable(network : Network) {
        Log.e(TAG, "The default network is now: " + network)
    }

    override fun onLost(network : Network) {
        Log.e(TAG, "The application no longer has a default network. The last default network was " + network)
    }

    override fun onCapabilitsChanged(network : Network, networkCapabilities : NetworkCapabilities) {
        Log.e(TAG, "The default network changed capabilities: " + networkCapabilities)
    }

    override fun onLinkPropertiesChanged(network : Network, linkProperties : LinkProperties) {
        Log.e(TAG, "The default network changed link properties: " + linkProperties)
    }
})

• AlertDialog 띄우기

private fun showAlert(){
    val builder = AlertDialog.Builder(this)
    builder.setTitle("")
        .setMessage("네트워크에 연결되지 않았습니다.")
        .setPositiveButton("다시 시도하기",
            DialogInterface.OnClickListener { dialog, id ->
                // 앱 처음부터 다시시작
                val intent = Intent(applicationContext, SplashActivity::class.java)
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP or Intent.FLAG_ACTIVITY_NEW_TASK)
                startActivity(intent)
                finish()
            })
    builder.show()
}