title: My switch (view.getId()) doesnt work
body: <p>I'm trying to work on an exercise, which means i need to change an image from an imageView with a button. The whole thing is implemented into another project of the exercise. </p>
  
  <p>The problem is: it doesn't even open the Toast "test" in the second case.</p>
  
  <pre><code>package de.vogella.android.temperature;
  
  import android.app.Activity;
  import android.graphics.drawable.Drawable;
  import android.os.Bundle;
  import android.view.View;
  import android.view.View.OnClickListener;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.ImageView;
  import android.widget.RadioButton;
  import android.widget.Toast;
  
  public class MainActivity extends Activity{
    private EditText text;
  
    @Override
    public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      text = (EditText) findViewById(R.id.editText1);
      Button button1 = (Button) findViewById(R.id.tempbutton);
      Button button2 = (Button) findViewById(R.id.imageconverter);
      OnClickListener listener = new OnClickListener() {
          @Override
          public void onClick(View v) {
              switch (v.getId()) {
                  case R.id.tempbutton:
                      button1Click();
                      break;
  
                  case R.id.imageconverter:
  
                      button2Click();
                      break;
              }
          }
      };
      button1.setOnClickListener(listener);
      button2.setOnClickListener(listener);
  
    }
  
  
  
  
    public void button1Click (){
        RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0);
          RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1);
          if (text.getText().length() == 0) {
          Toast.makeText(this, "Please enter a valid number",
          Toast.LENGTH_LONG).show();
          return;
          }
  
          float inputValue = Float.parseFloat(text.getText().toString());
          if (celsiusButton.isChecked()) {
          text.setText(String.valueOf(ConverterUtil.convertFahrenheitToCelsius(inputValue)));
          celsiusButton.setChecked(false);
          fahrenheitButton.setChecked(true);
          } else {
          text.setText(String
          .valueOf(ConverterUtil.convertCelsiusToFahrenheit(inputValue)));
          fahrenheitButton.setChecked(false);
          celsiusButton.setChecked(true);
          }
    }
  
    public void button2Click (){
        ImageView frontImageView = (ImageView) findViewById(R.id.myicon);
          frontImageView.setImageResource(R.drawable.assigned);
          Toast.makeText(this,"done", Toast.LENGTH_LONG).show();
    }
    }
  </code></pre>
  
  <p>XML File:</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:paddingBottom="@dimen/activity_vertical_margin"
      android:paddingLeft="@dimen/activity_horizontal_margin"
      android:paddingRight="@dimen/activity_horizontal_margin"
      android:paddingTop="@dimen/activity_vertical_margin"
      android:background="@color/myColor"
      tools:context=".MainActivity" &gt;
  
      &lt;EditText
          android:id="@+id/editText1"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignParentLeft="true"
          android:layout_alignParentTop="true"
          android:inputType="numberSigned|numberDecimal"
          android:ems="10" &gt;
  
          &lt;requestFocus /&gt;
      &lt;/EditText&gt;
  
      &lt;RadioGroup
          android:id="@+id/radioGroup1"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignLeft="@+id/editText1"
          android:layout_below="@+id/editText1" &gt;
  
          &lt;RadioButton
              android:id="@+id/radio0"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:checked="true"
              android:text="@string/celsius" /&gt;
  
          &lt;RadioButton
              android:id="@+id/radio1"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="@string/fahrenheit" /&gt;
      &lt;/RadioGroup&gt;
  
      &lt;Button
          android:id="@+id/tempbutton"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignLeft="@+id/radioGroup1"
          android:layout_below="@+id/radioGroup1"
          android:text="@string/calc"
          android:onClick="onClick" /&gt;
  
      &lt;TextView
          android:id="@+id/textView1"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignLeft="@+id/button1"
          android:layout_alignParentBottom="true"
          android:text="@string/author"
          android:textAppearance="?android:attr/textAppearanceSmall" /&gt;
  
      &lt;DigitalClock
          android:id="@+id/digitalClock1"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_above="@+id/textView1"
          android:layout_alignLeft="@+id/textView1"
          android:layout_alignRight="@+id/button1"
          android:text="DigitalClock" /&gt;
  
      &lt;Button
          android:id="@+id/imageconverter"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignBaseline="@+id/button1"
          android:layout_alignBottom="@+id/button1"
          android:layout_centerHorizontal="true"
          android:onClick="onClick"
          android:text="Change Image" /&gt;
  
      &lt;ImageView
          android:id="@+id/myicon"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignLeft="@+id/button2"
          android:layout_below="@+id/button2"
          android:src="@drawable/initial" /&gt;
  
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>LogCat:</p>
  
  <pre><code>02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.os.Handler.dispatchMessage(Handler.java:102)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.os.Looper.loop(Looper.java:136)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread.main(ActivityThread.java:5017)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at java.lang.reflect.Method.invokeNative(Native Method)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at java.lang.reflect.Method.invoke(Method.java:515)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at dalvik.system.NativeStart.main(Native Method)
  02-25 16:03:00.228: E/AndroidRuntime(1363): Caused by: java.lang.NullPointerException
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.Activity.findViewById(Activity.java:1884)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at de.vogella.android.temperature.MainActivity.&lt;init&gt;(MainActivity.java:24)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at java.lang.Class.newInstanceImpl(Native Method)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at java.lang.Class.newInstance(Class.java:1208)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
  02-25 16:03:00.228: E/AndroidRuntime(1363):     ... 11 more
  </code></pre>