title: Snackbar in Preferences Activity
body: <p>I'm trying to use snackbar with custom xml in my preferences activity. And i'm doing something wrong, because i get a nullpointer exception. I think it has something to do with the view, or maybe it`s because i don't use coordinator layout.
  Here is my Java code:</p>
  
  <pre><code>@Override
  public boolean onPreferenceChange(Preference preference, final Object newValue) {
      String key = preference.getKey();
      if (key.equals("distance")) {
          preference.setSummary((String) newValue);
          Snackbar snackbar = Snackbar
                  .make(findViewById(R.id.snackbarPosition), "You choose " + newValue, Snackbar.LENGTH_LONG)
                  .setAction("UNDO", new View.OnClickListener() {
                      @Override
                      public void onClick(View view) {
                          if (newValue.equals("km")){
                              SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(MyPrefs.this);
                              SharedPreferences.Editor editor = sp.edit();
                              editor.putString("distance", "miles");
                              editor.commit();
                          }else if (newValue.equals("miles")){
                              SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(MyPrefs.this);
                              SharedPreferences.Editor editor = sp.edit();
                              editor.putString("distance", "km");
                              editor.commit();
  
                          }
                      }
                  });
  
          snackbar.show();
  </code></pre>
  
  <p>Snackbar xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  </code></pre>
  
  <p></p>
  
  <pre><code>&lt;View
      android:id="@+id/sb__divider"
      android:layout_width="match_parent"
      android:layout_height="3dp" /&gt;
  
  &lt;LinearLayout
      android:id="@+id/sb__inner"
      android:background="@color/transparent_black_percent_70"
      android:layout_height="wrap_content"
      android:layout_width="match_parent"&gt;
  
      &lt;TextView
          android:id="@+id/sb__text"
          style="@style/Snackbar.Text"
          android:layout_width="0dp"
          android:layout_height="wrap_content"
          android:layout_weight="1"
          android:text="You choose blah blah"
          android:ellipsize="end"
          android:focusable="true" /&gt;
  
      &lt;Button
          android:id="@+id/sb__action"
          style="@style/Snackbar.Text.Action"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="center_vertical"
          android:text="undo"
          android:gravity="right"
          android:focusable="true" /&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p></p>
  
  <p>Preferences activity:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  </code></pre>
  
  <p></p>
  
  <pre><code>&lt;ListPreference
      android:dialogTitle="Select a distance system"
      android:entries="@array/distanceEntries"
      android:entryValues="@array/distanceValues"
      android:key="distance"
      android:title="Distance" /&gt;
  </code></pre>