title: Call method from Kotlin class
body: <p>I have an util Kotlin class where I set toolbar title, hide or show toolbar depends on the fragment:</p>
  
  <pre><code>class MyToolbarUtils() {
  
      fun hideToolbar(activity: Activity) {
          (activity as MainActivity).supportActionBar!!.hide()
      }
  
      fun showToolbar(activity: Activity, tag: String) {
          setToolbarTitle(tag, activity)
          (activity as MainActivity).supportActionBar!!.show()
      }
  
      fun setToolbarTitle(tag: String, activity: Activity) {
          var title = ""
          when (tag) {
              "Main_fragment" -&gt; title = activity.resources.getString(R.string.Main_screen)
              "Add_note" -&gt; title = activity.resources.getString(R.string.Add_note)
          }
          activity.title = title
      }
  }
  </code></pre>
  
  <p>how to call showToolbar(...) from Fragment?
  I just tried <code>MyToolbarUtils.showToolbar(..)</code> but it can not be possible</p>
  
  <p>only one way I discover is: </p>
  
  <pre><code>val setToolbarTitle = MyToolbarUtils()
  setToolbarTitle.showToolbar(activity, tag)
  </code></pre>
  
  <p>but there must be better way to do that..</p>