title: SeekBar secondaryProgress not showing
body: <p>I have a question, I have a seek bar and I want to show the buffer progress of an ExoPlayer media file using the secondary progress bar of the seekBar, the problem is that it´s not showing. Im running on API 21
  Here´s the xml code:</p>
  
  <pre><code>&lt;SeekBar
                  android:id="@+id/seekBarAudioA"
                  android:layout_width="100dp"
                  android:layout_height="wrap_content"
                  android:layout_alignParentLeft="true"
                  android:layout_alignParentStart="true"
                  android:layout_centerVertical="true"
                  android:maxHeight="3dip"
                  android:minHeight="3dip"
                  android:progressDrawable="@drawable/seek_bar_progress"
                  android:secondaryProgressTint="@android:color/holo_blue_dark"
                  android:thumbTint="@color/amber"
                  app:layout_constraintBottom_toBottomOf="@+id/play_pause"
                  app:layout_constraintHorizontal_bias="0.0"
                  app:layout_constraintLeft_toRightOf="@+id/play_pause"
                  app:layout_constraintRight_toRightOf="parent"
                  app:layout_constraintTop_toTopOf="@+id/play_pause" /&gt;
  </code></pre>
  
  <p>and here´s the java code:</p>
  
  <pre><code> SeekBar = new Thread(new Runnable() {
          @Override
          public void run() {
              try {
                  while (currentlyPlaying &amp;&amp; currentAudioHolder.getAdapterPosition() == audioPosition) {
                      int duration = (int) exoPlayer.getDuration();
                      currentAudioHolder.seekBarAudio.setMax(duration);
                      currentAudioHolder.seekBarAudio.setSecondaryProgress((int) exoPlayer.getBufferedPosition());
                      final int currPosition = (int) exoPlayer.getCurrentPosition();
                      Log.d("Buffer", "secondary progress bar position is: " + (int) exoPlayer.getBufferedPosition() + ", and the current position is: " + currPosition);
                      currentAudioHolder.seekBarAudio.setProgress(currPosition);
                      ((ChatActivity) context).runOnUiThread(new Runnable() {
                          @Override
                          public void run() {
                              currentAudioHolder.audioLength.setText(convertTime(currPosition));
                          }
                      });
                      Thread.sleep(sleep);
                  }
              } catch (InterruptedException i) {
                  currentlyPlaying = false;
              }
          }
      });
      SeekBar.start();
  </code></pre>
  
  <p>Please help :(</p>