build error

[lijain]

Gradel is OK when I compile the app, but the whole project will compile with an error.Baidu has been less than the problem, so send a post to ask you.Trouble you.
error description -----:
Build command failed.
Error while executing process D:\AndroidStudiosdk\cmake\3.10.2.4988404\bin\ninja.exe with arguments {-C D:\project_android\ncnn-android-nanodet-master\app.cxx\cmake\debug\armeabi-v7a nanodetncnn}
ninja: Entering directory `D:\project_android\ncnn-android-nanodet-master\app.cxx\cmake\debug\armeabi-v7a'
[1/4] Building CXX object CMakeFiles/nanodetncnn.dir/ndkcamera.cpp.o
FAILED: CMakeFiles/nanodetncnn.dir/ndkcamera.cpp.o
D:\AndroidStudiondk\android-ndk-r16b-windows-x86_64\android-ndk-r16b\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe --target=armv7-none-linux-androideabi --gcc-toolchain=D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64 --sysroot=D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/sysroot -Dnanodetncnn_EXPORTS -isystem D:/project_android/ncnn-android-nanodet-master/app/src/main/jni/ncnn-20201218-android-vulkan/armeabi-v7a/include/ncnn -isystem D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/sources/cxx-stl/gnu-libstdc++/4.9/include -isystem D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi-v7a/include -isystem D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/sources/cxx-stl/gnu-libstdc++/4.9/include/backward -isystem D:/AndroidStudiondk/android-ndk-r16b-windows-x86_64/android-ndk-r16b/sysroot/usr/include/arm-linux-androideabi -D__ANDROID_API__=24 -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -fno-integrated-as -mthumb -Wa,--noexecstack -Wformat -Werror=format-security -fopenmp=libomp -O0 -fno-limit-debug-info -fPIC -fno-rtti -fno-exceptions -MD -MT CMakeFiles/nanodetncnn.dir/ndkcamera.cpp.o -MF CMakeFiles\nanodetncnn.dir\ndkcamera.cpp.o.d -o CMakeFiles/nanodetncnn.dir/ndkcamera.cpp.o -c D:/project_android/ncnn-android-nanodet-master/app/src/main/jni/ndkcamera.cpp
In file included from D:/project_android/ncnn-android-nanodet-master/app/src/main/jni/ndkcamera.cpp:15:
D:/project_android/ncnn-android-nanodet-master/app/src/main/jni/ndkcamera.h:26:10: fatal error: 'opencv2/core/core.hpp' file not found
#include <opencv2/core/core.hpp>
^~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

private opinions:
Although looks like OpenCV problem, but I have changed the version to try several times also can't.NDK I have also changed it.So I want you to see what the problem is