Include DLL in `flutter build`

[Chris Norman]

Hi all,

I'm currently playing with Flutter for desktop, and I'd like to include a DLL with a release.

I know I need the dll alongside the eventual EXE, which is fine, but is there a way to make cmake put it there for me without me having to make a build script?

I've been googling to try and statically link the C++ code I'm using, but that doesn't seem to work, so now I'm trying a seemingly more simple step of having the DLL shipped with the application.

Thanks in advance,

Take care,

Chris Norman

[Daco Harkes]

Hey Chris,

This use case is supported by creating a plugin with flutter create -t plugin <name> and using the <name>_bundled_libraries field in the generated <name>\windows\CMakeLists.txt

# List of absolute paths to libraries that should be bundled with the plugin

set(<name>_bundled_libraries

"${CMAKE_CURRENT_SOURCE_DIR}/../native/lib/windows_x64/mylib_dylib.dll;${CMAKE_CURRENT_SOURCE_DIR}/../native/lib/windows_x64/mylib_dylib_dependency.dll"

PARENT_SCOPE

)

Note that I've put the precompiled libraries in <name>/native/lib/windows_x64 here.

If you're building from source, and you're willing to have the source code in a plugin project with it's own CMake build. Then you can invoke that build, and trigger the copy by copying it from the built plugin folder

# Invoke the build of mylib_source.

#

# Note that Flutter uses the Visual Studio compiler so the output dll will

# be in the Debug/ folder of the plugin.

include(${CMAKE_CURRENT_SOURCE_DIR}/../src/CMakeLists.txt)

# List of absolute paths to libraries that should be bundled with the plugin

set(mylib_source_bundled_libraries

"plugins/mylib_source/Debug/mylib_source.dll"

PARENT_SCOPE

)

A plugin project with a precompiled static library also works, but requires modification of the generated Flutter CMake file: flutter_app\linux\CMakeLists.txt

# Generated plugin build rules, which manage building the plugins and adding

# them to the application.

include(flutter/generated_plugins.cmake)

# Link static libraries from plugins into main executable with support for

# looking up symbols with dlsym. (Prefer using dynamic libraries over

# static libraries!)

foreach(plugin ${FLUTTER_PLUGIN_LIST})

if(${plugin}_linked_static_libraries)

# TODO(dacoharkes): Make it work for multiple static libraries.

target_link_libraries(

${BINARY_NAME}

PUBLIC

"${${plugin}_linked_static_libraries}"

)

set_target_properties(

${BINARY_NAME}

PROPERTIES

LINK_FLAGS

"/WHOLEARCHIVE:${plugin}"

)

endif()

endforeach(plugin)

And then you populate that variable in the plugin project again:

set(mylib_staticlib_linked_static_libraries

"${CMAKE_CURRENT_SOURCE_DIR}/../native/lib/windows_x64/mylib_staticlib.lib"

PARENT_SCOPE

)

This is slightly messy because it exposes all symbols. Without exposing all symbols the linker strips them away because no other C/C++ refers to them. So, you're better of using a dynamic library.

I'm in the process of adding these workflows to a new flutter create template. (Something "ffi plugin".)

I have not designed a workflow yet for directly embedding native code in an app without a plugin project. However, you should be able to achieve it by copying and modifying

if(PLUGIN_BUNDLED_LIBRARIES)

install(FILES "${PLUGIN_BUNDLED_LIBRARIES}"

DESTINATION "${INSTALL_BUNDLE_LIB_DIR}"

COMPONENT Runtime)

endif()

from flutter_app\windows\CMakeLists.txt and pointing it directly to your dynamic library.

Kind regards,

 •  Daco Harkes
 •  Software Engineer
 •  dacoh...@google.com 
 •  🔵 Blue Dot Ally

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