Problem mit Button und Listenern

1package com.example.taschenrechnerapp;
2
3import android.os.Bundle;
4import android.app.Activity;
5import android.view.Menu;
6import android.view.View;
7import android.view.View.OnClickListener;
8import android.widget.EditText;
9
10public class MainActivity extends Activity implements OnClickListener {
11 private EditText werteAnzeige;
12
13 @Override
14 public void onCreate(Bundle savedInstanceState) {
15 super.onCreate(savedInstanceState);
16
17 setContentView(R.layout.activity_main);
18
19 werteAnzeige = (EditText)findViewById(R.id.anzeigeWerte);
20
21 }
22
23@Override
24public boolean onCreateOptionsMenu(Menu menu) {
25 // Inflate the menu; this adds items to the action bar if it is present.
26 getMenuInflater().inflate(R.menu.main, menu);
27 return true;
28}
29
30@Override
31public void onClick(View v) {
32 switch(v.getId()){
33 case R.id.button_add:
34 werteAnzeige.setText("Add");
35 break;
36
37 case R.id.button_sub:
38 werteAnzeige.setText("Sub");
39 break;
40
41 case R.id.button_result:
42 werteAnzeige.setText("Result");
43 break;
44 }
45}
46}