Could not find a package configuration file provided by "qt_gui" with any
of the following names:
qt_guiConfig.cmake
qt_gui-config.cmake
不要去github里面下载,因为github提供的qt-gui是要配套ROS2的,要使用到ament_camke 可麻烦
sudo apt-get install ros-melodic-qt-gui
sudo apt-get install ros-melodic-qt-gui-cpp
这两个安装好了之后就ok了