where and how to enable CONFIG_DFU_TARGET_MCUBOOT


  I created my own application and want to enable CONFIG_DFU_TARGET_MCUBOOT.

But like the picture shows, this marco is still grey in the dfu_target_img_type() function. I already put CONFIG_DFU_TARGET_MCUBOOT=y in prj.conf fil, but after re-imported my project, this marco is still not enabled, and dfu_target_img_type() still returns "No supported image type found". i just want the red rectangle part of codes to run..