Get SSID when WIFI is connected

I listen for WifiManager.NETWORK_STATE_CHANGED_ACTION in a broadcast receiver

if (WifiManager.NETWORK_STATE_CHANGED_ACTION.equals(action)) {
    NetworkInfo netInfo = intent.getParcelableExtra (WifiManager.EXTRA_NETWORK_INFO);
    if (ConnectivityManager.TYPE_WIFI == netInfo.getType ()) {
        ...
    }
}

I check for netInfo.isConnected(). Then I am able to use

WifiManager wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
WifiInfo info = wifiManager.getConnectionInfo();
String ssid  = info.getSSID();

UPDATE

From android 8.0 onwards we wont be getting SSID of the connected network unless location services are enabled and your app has the permission to access it.

Starting with Android 8.1 (API 27), apps must be granted the ACCESS_COARSE_LOCATION (or ACCESS_FINE_LOCATION) permission in order to obtain results from WifiInfo.getSSID() or WifiInfo.getBSSID(). Apps that target API 29 or higher (Android 10) must be granted ACCESS_FINE_LOCATION.

This permission is also needed to obtain results from WifiManager.getConnectionInfo() and WifiManager.getScanResults() although it is not clear if this is new in 8.1 or was required previously.

Source: "BSSID/SSID can be used to deduce location, so require the same location permissions for access to these WifiInfo fields requested using WifiManager.getConnectionInfo() as for WifiManager.getScanResults()."

If you don't want to make Broadcast Receiver then simple try

WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
WifiInfo wifiInfo;

wifiInfo = wifiManager.getConnectionInfo();
if (wifiInfo.getSupplicantState() == SupplicantState.COMPLETED) {
    ssid = wifiInfo.getSSID();
}

Remember every time user disconnect or connect to new SSID or any wifi state change then you need to initialize WifiInfo i.e wifiInfo = wifiManager.getConnectionInfo();

I found interesting solution to get SSID of currently connected Wifi AP. You simply need to use iterate WifiManager.getConfiguredNetworks() and find configuration with specific WifiInfo.getNetworkId()

My example

in Broadcast receiver with action WifiManager.NETWORK_STATE_CHANGED_ACTION I'm getting current connection state from intent

NetworkInfo nwInfo = intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO);
nwInfo.getState()

If NetworkInfo.getState is equal to NetworkInfo.State.CONNECTED then i can get current WifiInfo object

WifiManager wifiManager = (WifiManager) getSystemService (Context.WIFI_SERVICE);
WifiInfo info = wifiManager.getConnectionInfo ();

And after that

public String findSSIDForWifiInfo(WifiManager manager, WifiInfo wifiInfo) {

    List<WifiConfiguration> listOfConfigurations = manager.getConfiguredNetworks();

    for (int index = 0; index < listOfConfigurations.size(); index++) {
        WifiConfiguration configuration = listOfConfigurations.get(index);
        if (configuration.networkId == wifiInfo.getNetworkId()) {
            return configuration.SSID;
        }
    }

    return null;
}

And very important thing this method doesn't require Location nor Location Permisions

In API29 Google redesigned Wifi API so this solution is outdated for Android 10.

In Android 8.1 it is must to turned Location on to get SSID, if not you can get connection state but not SSID

WifiManager wifiManager = (WifiManager) context.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
WifiInfo wifiInfo = null;
if (wifiManager != null) 
wifiInfo = wifiManager.getConnectionInfo();
 String ssid = null;
if (wifiInfo != null) 
ssid = wifiInfo.getSSID(); /*you will get SSID <unknown ssid> if location turned off*/