1.在xml布局文件中添加SeekBar：

2.在Activity中设置SeekBar.OnSeekBarChangeListener监听器，实现透明圆点的效果：

public class MainActivity extends AppCompatActivity implements SeekBar.OnSeekBarChangeListener {

private SeekBar seekBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    seekBar = findViewById(R.id.seekBar);
    seekBar.setOnSeekBarChangeListener(this);
}

@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
    //在SeekBar上添加透明圆点
    LayerDrawable layerDrawable = (LayerDrawable) seekBar.getProgressDrawable();
    Drawable circleDrawable = getResources().getDrawable(R.drawable.circle);
    layerDrawable.setDrawableByLayerId(android.R.id.secondaryProgress, circleDrawable);
}

@Override
public void onStartTrackingTouch(SeekBar seekBar) {
    //当开始拖动SeekBar时，将透明圆点设为不可见
    LayerDrawable layerDrawable = (LayerDrawable) seekBar.getProgressDrawable();
    Drawable circleDrawable = layerDrawable.findDrawableByLayerId(android.R.id.secondaryProgress);
    circleDrawable.setAlpha(0);
}

@Override
public void onStopTrackingTouch(SeekBar seekBar) {
    //当停止拖动SeekBar时，将透明圆点设为可见
    LayerDrawable layerDrawable = (LayerDrawable) seekBar.getProgressDrawable();
    Drawable circleDrawable = layerDrawable.findDrawableByLayerId(android.R.id.secondaryProgress);
    circleDrawable.setAlpha(255);
}

}

3.添加透明圆点的drawable资源文件，circle.xml：

这样，在拖动SeekBar时就会出现一个透明圆点跟随滑动。