Here are the coding tips that I think are worth sharing:
I added an LZ4 XCFramework into my Xcode project for an iOS app. Here is how:
. Download LZ4 source code
% git clone https://github.com/lz4/lz4.git
% cd lz4
. Compile for iOS device (arm64)
% make clean
% make liblz4.a TARGET_OS=iOS
% mv liblz4.a liblz4-ios-device.a
. Compile for iOS simulator (arm64 for Apple Silicon CPU, x86_64 for Intel CPU)
% make clean
% make liblz4.a TARGET_OS=iOSSimulator TARGET_ARCHS="arm64 x86_64"
% mv liblz4.a liblz4-ios-simulator.a
. Create XCFramework
% xcodebuild -create-xcframework -library liblz4-ios-device -headers /path/to/lz4/include -library liblz4-ios-simulator -headers /path/to/lz4/include -output liblz4-ios.xcframework
Here I got an error from xcodebuild -create-xcframework: A library with the identifier 'macos-arm64' already exists. Then I ran lipo -info to check architectures. lipo -info liblz4-ios-device.a output 'Non-fat file liblz4-ios-device.a is architecture: arm64'. This is expected. lipo -info liblz4-ios-simulator.a output 'Non-fat file liblz4-ios-simulator.a is architecture: arm64'. This is unexpected. The make command had ignored x86_64. So I had to build the library file for simulator manually:
% rm -v liblz4-ios-simulator.a
% make clean
#Build for x86_64
% clang -arch x86_64 -isysroot $(xcrun --sdk iphonesimulator --show-sdk-path) -c lib/lz4.c -o liblz4-ios-simulator-x86_64.o
#Build for arm64
% clang -arch arm64 -isysroot $(xcrun --sdk iphonesimulator --show-sdk-path) -c lib/lz4.c -o liblz4-ios-simulator-arm64.o
#Create static libraries
% ar rcs liblz4-ios-simulator-x86_64.a liblz4-ios-simulator-x86_64.o
% ar rcs liblz4-ios-simulator-arm64.a liblz4-ios-simulator-arm64.o
#Merge into a fat library
% lipo -create -output liblz4-ios-simulator.a liblz4-ios-simulator-x86_64.a liblz4-ios-simulator-arm64.a
Then I ran lipo -info liblz4-ios-simulator.a, it output 'Architectures in the fat file: liblz4-ios-simulator.a are: arm64 x86_64'. I ran the xcodebuild -create-xcframework, I got the liblz4-ios.xcframework. I ls liblz4-ios.xcframework, I found it had subdirectories: ios-arm64_x86_64-simulator/, macos-arm64/. The ios-arm64_x86_64-simulator/ one is expected, but the macos-arm64/ is not expected, it should be ios-arm64/.
Then I cleaned the previously made liblz4-ios-device.a, remade the library with
% clang -arch arm64 -isysroot $(xcrun --sdk iphoneos --show-sdk-path) -miphoneos-version-min=12.0 -c lib/lz4.c -o liblz4-ios-device.o
% ar rcs liblz4-ios-device.a liblz4-ios-device.o
The -miphoneos-version-min option explicitly makes the object file for iOS, not macOS. I reran the xcodebuild -create-xcframework, in the resultant liblz4-ios.xcframework, the expected ios-arm64/ appeared; it has the library liblz4-ios-device.a.
. Drag and drop the liblz4-ios.xcframework into Xcode's Frameworks and Libraries section.
. Done.
. Download CFITSIO source with
% curl -O https://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/cfitsio_latest.tar.gz
% tar -xvf cfitsio_latest.tar
% cd cfitsio
. Compile CFITSIO for iOS device with
% make distclean
% ./configure --host=arm-apple-darwin --with-bzip2 --with-zlib CC="$(xcrun --sdk iphoneos --find clang)" CFLAGS="-arch arm64 -isysroot $(xcrun --sdk iphoneos --show-sdk-path) -miphoneos-version-min=12.0" --prefix="/path/to/install/into"
% make
% make install
% cp -v /path/to/install/into/lib/libcfitsio.a /my/lib/libcfitsio-ios-device.a
In here, I ran into an error at make install: cfileio.c:14:12: fatal error: curl/curl.h file not found. Then I added --disable-curl option for configure, cause I don't need remote file access via HTTP/FTP. Then I ran make, the curl problem seemed okay, but I saw error: utilities/fpackutil.c:926:17: error: 'system' is unavaliable: not available on iOS. The system() function is not available on iOS for security reasons. So I found the line system(command) in fpackutil.c and commented it out. Then I successfully built the library file for ios device.
. Compile for iOS simulator (arm64) with
% make distclean
% ./configure --host=arm-apple-darwin --with-bzip2 --with-zlib --disable-curl CC="$(xcrun --sdk iphonesimulator --find clang)" CFLAGS="-arch arm64 -isysroot $(xcrun --sdk iphonesimulator --show-sdk-path) -mios-simulator-version-min=12.0" --prefix="/path/to/install/into"
% make
% make install
% cp -v /path/to/install/into/lib/libcfitsio.a /my/lib/libcfitsio-iossimulator-arm64.a
. Compile for iOS simulator (x86_64) with
% make distclean
% ./configure --host=arm-apple-darwin --with-bzip2 --with-zlib --disable-curl CC="$(xcrun --sdk iphonesimulator --find clang)" CFLAGS="-arch x86_64 -isysroot $(xcrun --sdk iphonesimulator --show-sdk-path) -mios-simulator-version-min=12.0" --prefix="/path/to/install/into"
% make
% make install
% cp -v /path/to/install/into/lib/libcfitsio.a /my/lib/libcfitsio-iossimulator-x86_64.a
. Create universal simulator library with
% cd /my/lib
% lipo -create libcfitsio-iossimulator-arm64.a libcfitsio-iossimulator-x86_64.a -output libcfitsio-ios-simulator.a
. Create XCFramework with
% xcodebuild -create-xcframework -library libcfitsio-ios-device.a -headers /path/to/install/into/include -library libcfitsio-ios-simulator.a -headers /path/to/install/into/include -output libcfitsio-ios.xcframework
. Drag and drop the libcfitsio-ios.xcframework into Xcode's Frameworks and Libraries section.
. Done.
. When I built my Xcode project, I got a warning and an error.
The warning is duplicate output file '/Users/<usrname>/Library/Developer/Xcode/DerivedData/<app>-<hash code>/Build/Products/Debug-iphoneos/include/lz4.h' on task: ProcessXCFramework /path/to/app/liblz4-ios.xcframework /Users/<usrname>/Library/Developer/Xcode/DerivedData/<app>-<hash code>/Build/Products/Debug-iphoneos/liblz4-ios-device.a ios.
The error is Multiple commands produce '/Users/<usrname>/Library/Developer/Xcode/DerivedData/<app>-<hash code>/Build/Products/Debug-iphoneos/include/lz4.h'; Command: ProcessXCFramework /path/to/app/libcfitsio-ios.xcframework /Users/<usrname>/Library/Developer/Xcode/DerivedData/<app>-<hash code>/Build/Products/Debug-iphoneos/libcfitsio-ios-device.a ios; Command: ProcessXCFramework /path/to/app/liblz4-ios.xcframework /Users/<usrname>/Library/Developer/Xcode/DerivedData/<app>-<hash code>/Build/Products/Debug-iphoneos/liblz4-ios-device.a ios.
As I had also added an LZ4 framework into the project, this error happened because both libcfitsio-ios.xcframework and liblz4-ios.xcframework include the same header file lz4.h. To fix this issue, I rebuilt libcfitsio-ios.xcframework with exluding LZ4 headers by adding -I/path/to/lz4/include to CFLAGS and adding -L/path/to/lz4/lib -llz4-ios-device/-llz4-iossimulator-arm64/-llz4-iossimulator-x86_64 to LDFLAGS for configure.
. Really done.