Check Internet

 android:onClick="checkInternet"

Java

 public void checkInternet(View view) {

        if (!isConnected(this)){

            showCustomDialog();

        }

        Intent categoryIntent = new Intent(MainActivity.this,CategoryActivity.class);

        startActivity(categoryIntent);

    }

    private boolean isConnected(MainActivity mainActivity) {

        ConnectivityManager connectivityManager = (ConnectivityManager) mainActivity.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo wifiConnection = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

        NetworkInfo mobileConnection = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

        if ((wifiConnection != null && wifiConnection.isConnected())

                || (mobileConnection != null && mobileConnection.isConnected())){

            return true;

        }else{

            return false;

        }

    }

    private void showCustomDialog() {

        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

        builder.setMessage("Please connect to the internet")

               .setCancelable(false)

               .setPositiveButton("Connect", new DialogInterface.OnClickListener() {

            @Override

            public void onClick(DialogInterface dialog, int which) {

                startActivity(new Intent(Settings.ACTION_WIFI_SETTINGS));

            }

        })

                .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        startActivity(new Intent(getApplicationContext(),MainActivity.class));

                        finish();

                    }

                });

    }