Die erste App - activity_main u. fragment_main

package de.arduinoredfly_01_menue;

import java.net.InetAddress;
import java.net.InetSocketAddress;

import de.arduinoredfly_01_menue.R;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.pm.ActivityInfo;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Build;
import android.preference.PreferenceManager;

public class MainActivity extends Activity {
    
    WifiManager wifi;
    TextView textStatus;
    ArduinoredflyCommManager commMan;
    SharedPreferences prefs;


    //Erstellen des Menü´s
    public boolean onCreateOptionsMenu(Menu menu) {
        
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

  //Erstellen des Einstellungen-Eintrags
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
    
    
  //Erstellen des Layouts
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        //Fixieren auf Porträt-Orientierung (kein automatisches Bildschirmdrehen)
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        prefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
        commMan = new ArduinoredflyCommManager();
        
        //Ausgeben simpler WLAN-Verbindungseigenschaften
        //textStatus = (TextView) findViewById(R.id.textStatus);
        //wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        //WifiInfo info = wifi.getConnectionInfo();
        //textStatus.setText("WiFi Status: " + info.toString());
        
        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }
    

    // A placeholder fragment containing a simple view.
    public static class PlaceholderFragment extends Fragment {
        
        public PlaceholderFragment() {
        }
        
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }
    }
    
    //Eventhandler für Change-Events an den Buttons (drücken)
    public void myClickHandler(View view) {
        InetAddress address;
        
        try {
            //IP festlegen
            address = InetAddress.getByName("192.168.43.57");
        }catch (Exception ex){
            Toast.makeText(this, "IP nicht erreichbar",
                    Toast.LENGTH_LONG).show();
            return;
        }
        try{
            int pin;
            
            //Port festlegen
            int port = 22;
            
            switch (view.getId()) {
            case R.id.btn_pin8_ein:
                pin = 8;
                commMan.sendDigitalCommand(pin, true, address, port);
                break;
            case R.id.btn_pin9_ein:
                pin = 9;
                commMan.sendDigitalCommand(pin, true, address, port);
                break;
            case R.id.btn_pin8_aus:
                pin = 8;
                commMan.sendDigitalCommand(pin, false, address, port);
                break;
            case R.id.btn_pin9_aus:
                pin = 9;
                commMan.sendDigitalCommand(pin, false, address, port);
                break;
            default:
                return;
            }

        }catch (Exception ex){
            Toast.makeText(this, "Problem xyz",
                    Toast.LENGTH_LONG).show();
        }
    }
}