constraintlayout Placeholder :The previous view is always visible.

[qhyuan]

 public void setContentId(int id) {
    if (mContentId == id) {
      return;
    }
    if (mContent != null) {
      mContent.setVisibility(VISIBLE); // ???----------------> Why VISIBLE???<-----------------------------
      ConstraintLayout.LayoutParams layoutParamsContent = (ConstraintLayout.LayoutParams) mContent
          .getLayoutParams();
      layoutParamsContent.isInPlaceholder = false;
      mContent = null;
    }
    mContentId = id;
    if (id != ConstraintLayout.LayoutParams.UNSET) {
      View v = ((View) getParent()).findViewById(id);
      if (v != null) {
        v.setVisibility(GONE);
      }
    }
  }

How about add a function：
fun setContentId(id: Int, @Visibility preViewVisibility: Int = View.GONE)
Thanks~!