How to write Android code for internet connection?

Question

How to build app with internet connection?

if there is no internet it have to show one alert box

MainActivity.java

     public class MainActivity extends AppCompatActivity {
    ConnectivityManager connectivityManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        String macadd = wifiManager.getConnectionInfo().getMacAddress();
        BluetoothAdapter BA = BluetoothAdapter.getDefaultAdapter();
        if (!BA.isEnabled()) {
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
            builder.setTitle("PLEASE READ THE FOLLOWING");
            builder.setMessage("Please On Your Bluetooth");
            builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    finish();

                }
            });
            AlertDialog alertDialog = builder.create();
            alertDialog.setCancelable(false);
            alertDialog.show();
        }
 }

Answer 1

ManifestPermssions:

<uses-permission android:name="android.permission.INTERNET" />

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Check for runtime permission for android targeting android 6.0 and upward.

public class MainActivity extends AppCompatActivity {
    Context context;
    private static final int REQUEST_RUNTIME_PERMISSION = 123;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        context = this;

        if (CheckPermission(MainActivity.this, Manifest.permission.ACCESS_NETWORK_STATE)) {
            // you have permission go ahead
            checkIntetnetConnection();
        } else {
            // you do not have permission go request runtime permissions
            RequestPermission(MainActivity.this, Manifest.permission.ACCESS_NETWORK_STATE, REQUEST_RUNTIME_PERMISSION);
        }

    }

    private void checkIntetnetConnection() {
        if (isNetworkAvailable()) {
        } else {
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
            builder.setTitle("PLEASE READ THE FOLLOWING");
            builder.setMessage("Please On Your Bluetooth");
            builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    finish();

                }
            });
            AlertDialog alertDialog = builder.create();
            alertDialog.setCancelable(false);
            alertDialog.show();
        }
    }

    private boolean isNetworkAvailable() {
        ConnectivityManager connectivityManager
                = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        return activeNetworkInfo != null && activeNetworkInfo.isConnected();
    }

    @Override
    public void onRequestPermissionsResult(int permsRequestCode, String[] permissions, int[] grantResults) {
        switch (permsRequestCode) {

            case REQUEST_RUNTIME_PERMISSION: {
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    // you have permission go ahead
                    checkIntetnetConnection();
                } else {
                    // you do not have permission show toast.
                }
                return;
            }
        }
    }

    public void RequestPermission(Activity thisActivity, String Permission, int Code) {
        if (ContextCompat.checkSelfPermission(thisActivity,
                Permission)
                != PackageManager.PERMISSION_GRANTED) {
            if (ActivityCompat.shouldShowRequestPermissionRationale(thisActivity,
                    Permission)) {
            } else {
                ActivityCompat.requestPermissions(thisActivity,
                        new String[]{Permission},
                        Code);
            }
        }
    }

    public boolean CheckPermission(Context context, String Permission) {
        if (ContextCompat.checkSelfPermission(context,
                Permission) == PackageManager.PERMISSION_GRANTED) {
            return true;
        } else {
            return false;
        }
    }
}