Question

The first time I enable Wifi and then disable it everything is fine, but if I try to re-enable the Wifi after (either immediately or waiting for mobile data to connect again) it throws a NullPointerException and Force Closes.

private void toggleWifi(){

    if (wifi == 0){
        wifiManager.setWifiEnabled(true);
        scanOnly = wifiManager.createWifiLock(WifiManager.WIFI_MODE_SCAN_ONLY, "scanOnly");
        scanOnly.acquire();

        bWifi.setText("Turn Wifi OFF");

        List<ScanResult> wifiResults = wifiManager.getScanResults();

        StringBuilder sb = new StringBuilder("Scan Results:\n");            
        sb.append("-----------------------\n");

        for (ScanResult r : wifiResults) {
            sb.append(r.SSID + " " + r.level + " dBM\n");
        }

        tvWifi.setText(sb.toString());

        wifi = 1;

    } else {
        scanOnly.release();
        wifiManager.setWifiEnabled(false);

        bWifi.setText("Turn WiFi ON");

        tvWifi.setText("");

        wifi = 0;
    }

}

The error is on this line:

for (ScanResult r : wifiResults) {
    sb.append(r.SSID + " " + r.level + " dBM\n");
}

Answer 1

Have you tried debug? It’s possible that wifiResults is null at the moment