安卓 ndk(cmake) : 'undefined reference to ` __android_log_write' when using log api in the second jni library

Question

我使用 Android Studio 2.2 和 cmake 构建 jni 文件。

我想在 jni 文件中显示日志，但收到错误消息“对 `__android_log_write 的 undefined reference ”。

我的 CMakeLists.txt 文件是:

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).
         # Associated headers in the same location as their source
         # file are automatically included.
         src/main/cpp/native-lib.cpp )

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

         # Sets the library as a shared library.
         SHARED

         # Provides a relative path to your source file(s).
         # Associated headers in the same location as their source
         # file are automatically included.
         src/main/cpp/test-lib.cpp )

include_directories( src/main/jni/ )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because system libraries are included 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 )

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

target_link_libraries( # Specifies the target library.
                   test-lib
                   native-lib
                   # Links the target library to the log library
                   # included in the NDK.
                   ${log-lib} )

而我的两个jni文件都是一样的，没有函数名

JNIEXPORT jstring JNICALL Java_com_cyweemotion_www_jnitest_MainActivity_stringFromJNI
    (JNIEnv *env, jobject){
    __android_log_write(ANDROID_LOG_ERROR, "Tag", "Error here");
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
};

我的 build.gradle(Module:app) 是

    android {
    compileSdkVersion 23
    buildToolsVersion "24.0.3"
    defaultConfig {
        minSdkVersion 19
        targetSdkVersion 24
        versionCode 2
        versionName '1.02'
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ""
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            signingConfig signingConfigs.config
        }
        debug {
            jniDebuggable false
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    productFlavors {
    }
}

根据android document:Add C and C++ Code to Your Project .我想我可以使用日志 api。

我的代码或我的设置有什么问题？

---

更新:

我发现在我的第一个 jni 库中没有问题(更新代码)。

它只在第二个库中发生错误。

ex: target_link_libraries(test-lib, native-lib, ...), native-lib 是第二个要加载的库。

所以 native-lib 不能使用 log api。

现在我唯一能做的就是移除 native-lib。但是我真的很想知道为什么？

Answer 1

我终于发现我应该分开做链接。

target_link_libraries( # Specifies the target library.
                   test-lib
                   native-lib
                   # Links the target library to the log library
                   # included in the NDK.
                   ${log-lib} )

target_link_libraries( # Specifies the target library.
                   native-lib
                   # Links the target library to the log library
                   # included in the NDK.
                   ${log-lib} )