A HorizontalScrollView is a
FrameLayout, meaning you should place one child in it containing the entire contents to scroll; this child may itself be a layout manager with a complex hierarchy of objects. A child that is often used is a
LinearLayout in a horizontal orientation, presenting a horizontal array of top-level items that the user can scroll through.
TextView class also takes care of its own scrolling, so does not require a HorizontalScrollView, but using the two together is possible to achieve the effect of a text view within a larger container.
Right click on the project folder > Android tools > Clear Link Markers
“Run Android Lint” makes some markers and the markers cause this error.