Install libqgis-customwidgets by entering the following commands in the terminal:
sudo apt update sudo apt install libqgis-customwidgets
Description:
QGIS custom widgets for Qt Designer
QGIS is a Geographic Information System (GIS) which manages, analyzes and display databases of geographic information. . This package contains a library to use specific QGIS widgets in Qt Designer.
Homepage: https://qgis.org/
Version: 2.18.17+dfsg-1
Section: universe/science