PN532库与Android应用同步失败：CMake配置报错求助

在Android项目中集成libnfc库（用于PN532读卡器），编写了CMakeLists.txt和native-lib.cpp，但同步Gradle时出现错误：

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.

我的CMakeLists.txt #

# Minimum version of CMake required
cmake_minimum_required(VERSION 3.18.1)

# Project name
project(nfc_app)

# Specify the library to be built as a shared library
add_library(
        # Name of the library to be built (native JNI library)
        nfc_native_lib  # This should be a logical name for the library

        # Build as a shared library
        SHARED

        # Add your native source files here
        src/main/cpp/native-lib.cpp  # Ensure this is the correct path
)

# Set the path to the libnfc header files (should point to headers, not .so)
include_directories(
        ${CMAKE_SOURCE_DIR}/src/main/jniLibs/libnfc.so/libnfc/pn532.h  # Path to libnfc headers (.h files)
)

# Find the libnfc library
find_library(
        libnfc-lib  # Variable to store the result of the find
        nfc         # Name of the library (libnfc.so is what will be searched)
        PATHS ${CMAKE_SOURCE_DIR}/src/main/jniLibs/armeabi-v7a  # Path where .so file is located
)

# Set path to additional libraries if required (for example, if libnfc is in a custom directory)
# You can adjust this path as per your project structure
link_directories(${CMAKE_SOURCE_DIR}/src/main/jniLibs/arm64-v8a)

# Link the native library with libnfc and any other necessary libraries (e.g., log for logging)
target_link_libraries(
        nfc_native_lib       # The JNI library you're building (same name as in add_library)
        ${libnfc-lib}         # Link libnfc (found using find_library)
        log                   # Optional: Android NDK logging library
)

我的native-lib.cpp #

#include <jni.h>
#include <nfc/nfc.h>  // Include libnfc headers

JNIEXPORT jstring  extern "C" JNICALL
Java_com_example_nfc_app_MainActivity_readNFC(JNIEnv *env, jobject thiz) 
    // Use libnfc functions here
    nfc_device *device = NULL;  // Declare the NFC device pointe

    // Initialize libnfc, interact with the NFC reader (PN532), etc.
    nfc_context *context;
    nfc_init(&context);

    if (context == NULL) {
        return env->NewStringUTF("Failed to initialize libnfc");
    }

    // Open the NFC device
    device = nfc_open(context, NULL);  // NULL means using the first available device
    if (device == NULL) {
        nfc_exit(context);
        return env->NewStringUTF("Failed to open NFC device");
   }

CMakeLists.txt的问题与修复 #

1. include_directories路径错误：该指令需要指向包含头文件的目录，而非单个头文件。假设nfc.h、pn532.h等头文件都在src/main/jniLibs/include/libnfc/目录下，修改为：

include_directories(
        ${CMAKE_SOURCE_DIR}/src/main/jniLibs/include/
)

2. 架构路径不一致：find_library指定了armeabi-v7a，但link_directories用了arm64-v8a，导致CMake无法匹配对应架构的库。建议用${ANDROID_ABI}自动适配当前编译架构：

# 统一架构路径
set(LIBNFC_PATH ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI})

# 查找libnfc库
find_library(
        libnfc-lib
        nfc
        PATHS ${LIBNFC_PATH}
        NO_DEFAULT_PATH  # 仅在指定路径查找，避免系统库干扰
)

# 添加链接目录
link_directories(${LIBNFC_PATH})

3. 校验库文件存在性：确认src/main/jniLibs/${ANDROID_ABI}/目录下存在libnfc.so文件（find_library查找的nfc对应文件名libnfc.so）。

修复后的完整CMakeLists.txt：

cmake_minimum_required(VERSION 3.18.1)
project(nfc_app)

add_library(
        nfc_native_lib
        SHARED
        src/main/cpp/native-lib.cpp
)

# 指向libnfc头文件所在目录（根据实际路径调整）
include_directories(
        ${CMAKE_SOURCE_DIR}/src/main/jniLibs/include/
)

# 适配当前编译架构
set(LIBNFC_PATH ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI})

find_library(
        libnfc-lib
        nfc
        PATHS ${LIBNFC_PATH}
        NO_DEFAULT_PATH
)

link_directories(${LIBNFC_PATH})

target_link_libraries(
        nfc_native_lib
        ${libnfc-lib}
        log
)

native-lib.cpp的问题与修复 #

1. 函数体缺少大括号：Java_com_example_nfc_app_MainActivity_readNFC函数未用大包裹代码块，导致语法错误。
2. 变量拼写错误：NFC device pointe应为NFC device pointer。
3. 缺少返回值与资源清理：函数结尾需添加返回语句，以及打开设备成功后的资源释放逻辑。

修复后的native-lib.cpp：

#include <jni.h>
#include <nfc/nfc.h>

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_nfc_app_MainActivity_readNFC(JNIEnv *env, jobject thiz) {
    nfc_device *device = NULL;  // Declare the NFC device pointer
    nfc_context *context;
    nfc_init(&context);

    if (context == NULL) {
        return env->NewStringUTF("Failed to initialize libnfc");
    }

    device = nfc_open(context, NULL);
    if (device == NULL) {
        nfc_exit(context);
        return env->NewStringUTF("Failed to open NFC device");
    }

    // 此处可添加NFC标签读取逻辑

    // 清理资源
    nfc_close(device);
    nfc_exit(context);
    return env->NewStringUTF("NFC device opened successfully");
}

最后检查 #

• 确认libnfc的头文件和.so文件路径与CMakeLists.txt配置一致。
• 在app模块的build.gradle中指定支持的ABIs：

android {
    defaultConfig {
        ndk {
            abiFilters 'armeabi-v7a', 'arm64-v8a'
        }
    }
}

内容的提问来源于stack exchange，提问作者Wan Ammar