错误:对'oboe::AudioStreamBuilder::openStream(oboe::AudioStream**)‘的未定义引用

Question

我正在尝试使用我的Android应用程序中的Google。当我尝试使用来自本地lib.cpp的双簧管：：AudioStreamBuilder时，一切都很好。但是，当我尝试从类中使用双簧管：：AudioStreamBuilder时，我会得到错误消息" error :在重建项目时对'oboe::AudioStreamBuilder::openStream(oboe::AudioStream**)'“的未定义引用”。

这里是本机-lib.cpp，没关系：

#include <jni.h>
#include <string>
#include <android/log.h>
#include "OboeAudioRecorder.h"

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_oboeaudiorecorder_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}


extern "C" JNIEXPORT jboolean JNICALL
Java_com_example_oboeaudiorecorder_MainActivity_recordAudio(
        JNIEnv * env,
        jobject MainActivity
) {
    oboe::AudioStreamBuilder builder;
    builder.setDirection(oboe::Direction::Input);
    builder.setPerformanceMode(oboe::PerformanceMode::LowLatency);
    builder.setDeviceId(0);

    oboe::AudioStream *stream;
    oboe::Result r = builder.openStream(&stream);
    if (r != oboe::Result::OK) {
        return false;
    }

    return true;
}

下面是无法编译的类：

#include <oboe/Oboe.h>
#include <oboe/AudioStreamBuilder.h>
#include "OboeAudioRecorder.h"

OboeAudioRecorder::OboeAudioRecorder() {

    oboe::AudioStreamBuilder builder;
    builder.setDirection(oboe::Direction::Input);
    builder.setPerformanceMode(oboe::PerformanceMode::LowLatency);
    builder.setDeviceId(0);

    oboe::AudioStream *stream;
    oboe::Result r = builder.openStream(&stream);
    if (r != oboe::Result::OK) {
        return;
    }

}

CMakeLists.txt文件：

# 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 3.4.1)

# <Begin> OBOE SPECIFIC
# Set the path to the Oboe directory.
set (OBOE_DIR "../../../../../oboe")

# Add the Oboe library as a subdirectory in your project.
# add_subdirectory tells CMake to look in this directory to
# compile oboe source files using oboe's CMake file.
# ./oboe specifies where the compiled binaries will be stored
add_subdirectory (${OBOE_DIR} ./oboe)

# Specify the path to the Oboe header files.
# This allows targets compiled with this CMake (application code)
# to see public Oboe headers, in order to access its API.
include_directories (${OBOE_DIR}/include)
# <End> OBOE SPECIFIC

# 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.

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 )

add_library(
        OboeAudioRecorder
        SHARED
        OboeAudioRecorder.cpp
)

# 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 )

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

Answer 1

在您的CMakeLists.txt更改：

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 )

至

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
             OboeAudioRecorder.cpp
 )

并删除对OboeAudioRecorder的所有其他引用。

为什么这样做？

使用下面的行，您将尝试构建另一个名为OboeAudioRecorder的库

add_library(
        OboeAudioRecorder
        SHARED
        OboeAudioRecorder.cpp
)

这个库依赖于oboe，但是您没有在任何地方指定该库，您只指定了native-lib库的依赖项：

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

这就是在链接error: undefined reference库时获得OboeAudioRecorder的原因。

您可以添加第二行target_link_libraries(OboeAudioRecorder oboe)，但我猜您不需要两个单独的库，您只需要一个依赖于oboe的库。