为什么 CMake 没有与我的自定义库（add_library/set_property）链接？

Question

我已经看到this question 的答案对我来说太宽泛了。显然这是一个仅与 Cmakelists.txt 相关的问题。

我正在尝试将动态 (.so) 本机库与支持 JNI 的现有 Android 应用程序集成。

所以基本上，这个项目已经包含了一个共享本机库，该库将使用其他共享本机库。在我的例子中，它被称为 libcardios，它将被 native-lib.cpp 调用。

我想我这里有一个 CMakeLists.txt 问题，因为链接器命令根本不包含对我的共享库的引用：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.10.2)

# Declares and names the project.

project("myhelloworldapplication")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

# the file list must be regenerated each time the repo is updated from bitbucket
# You can use a shell command like this one:
# find . -name '*.cpp' > source_code_list.txt
# then remove the portion of the path you do not want

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             native-lib.cpp
             )

# The folder list may have changed /!\
# Make sure to have it in sync with the repo

target_include_directories(native-lib PUBLIC
        libcardios/includes
        )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

find_library( # Sets the name of the path variable.
        android-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        android )

add_library(libcardios_lib SHARED IMPORTED)
set_property(TARGET libcardios_lib PROPERTY IMPORTED_LOCATION "libcardios/${CMAKE_ANDROID_ARCH_ABI}/libcardios.so")

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib}
                        ${android-lib}
                        ${libcardios_lib}
                        )

这里是 build.gradle 文件的相关部分：

plugins {
    id 'com.android.application'
}

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.2"

    defaultConfig {
        applicationId "com.example.myhelloworldapplication"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                    cppFlags "-v -std=c++11 -fexceptions"
                }
        }
        ndk {
            abiFilters "armeabi-v7a"
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'com.google.android.material:material:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

最后是链接器命令的详细输出，它没有任何 libcardios 库的踪迹。

 "/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/bin/ld" --sysroot=/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot -z noexecstack -EL --warn-shared-textrel -z now -z relro -X --hash-style=both --enable-new-dtags --eh-frame-hdr -m armelf_linux_eabi -shared -o /Users/omatrot/Documents/sensoria_analyics/simpleandroidappwithlibcardios/app/build/intermediates/cmake/debug/obj/armeabi-v7a/libnative-lib.so /Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi/16/crtbegin_so.o -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/9.0.8/lib/linux/arm -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/armv7-a/thumb -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/lib/../lib/armv7-a/thumb -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi/16 -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/../lib -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi/../../lib -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/lib/armv7-a/thumb -L/Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib --exclude-libs libgcc.a --exclude-libs libgcc_real.a --exclude-libs libatomic.a --build-id --fatal-warnings --exclude-libs libunwind.a --no-undefined -soname libnative-lib.so CMakeFiles/native-lib.dir/native-lib.cpp.o -llog -landroid -latomic -lm -Bstatic -lc++ -Bdynamic -lm -lgcc -ldl -lc -lgcc -ldl /Users/omatrot/Library/Developer/Xamarin/android-sdk-macosx/ndk/21.1.6352462/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi/16/crtend_so.o
  /Users/omatrot/Documents/sensoria_analyics/simpleandroidappwithlibcardios/app/src/main/cpp/native-lib.cpp:16: error: undefined reference to 'CardioS::init()'
  clang++: error: linker command failed with exit code 1 (use -v to see invocation)

问题可能出在哪里？这是 CMakeLists.txt 中指令的错误顺序吗？在我看来，${libcardios_lib} 只是空的......

任何帮助表示赞赏。

Answer 1

与使用 add_library 创建的任何其他库一样，与 IMPORTED 库的链接是使用其名称执行的，无需取消引用它。

取消引用 (${...}) 应用于变量，但add_library 创建的是目标，而不是变量。 p>

add_library(libcardios_lib SHARED IMPORTED)
...
# Correct usage of the library:
target_link_libraries(native-lib PUBLIC libcardios_lib)
# Incorrect:
target_link_libraries(native-lib PUBLIC ${libcardios_lib})