Unknown CMake command "kde4_add_ui_files"

If you get this error

Unknown CMake command "kde4_add_ui_files"

while trying to use cmake, it usually means that

find_package(KDE4 REQUIRED)

is missing from the CMakeLists.txt file. Try adding it to the CMakeLists.txt file somewhere before kde4_add_ui_files is first called.

An example
project(plasma-network)

set(network_SRCS
network.cpp)

kde4_add_ui_files(network_SRCS config.ui )

becomes:
project(plasma-network)

set(network_SRCS
network.cpp)

find_package(KDE4 REQUIRED)

kde4_add_ui_files(network_SRCS config.ui )

See here for more information: http://www.vtk.org/Wiki/CMake:How_To_Build_KDE4_Software#Where_to_find_more_information .g

By the way, the same line helps for problems with "macro_optional_find_package" and most other KDE compilation problems.