title: Android/Kotlin Material Button checkedId, what is it?
body: <p>Wonder if anyone can tell me what exactly the <code>checkedId</code> of a Material Button is? The documentation is not very clear. For instance:</p>
  <pre><code>button.addOnButtonCheckedListener { group, checkedId, isChecked -&gt; stuff e.g. Toast}
  </code></pre>
  <p>For the <code>checkedId</code>, I get a long integer. For instance, I have a button with XML ID <code>android:id=&quot;@+id/paletteF&quot;</code>, and when I click it the <code>checkedId</code> returns as <code>2131362134</code>. I don't see an obvious correlation here, if there is one... Is it an address??</p>