c++ - 如何将 "jni/*.c/cpp"文件添加到 CMakeLists.txt 文件？

Question

我创建了一个包含 C++ NDK 的新项目。所以它自动创建了一个CMakeLists.txt文件和一个cpp目录。但是当我创建一个名为 jni 的新目录并尝试放入 test.c、Android.mk 和 Application.mk 文件，当我想同步我的项目时收到此错误消息:

This file is not part of the proejct.please include it to appropriaten build file

安卓.mk:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := ndktest
LOCAL_SRC_FILES := test.c

应用程序.mk:

APP_ABI := all

测试.c:

#include <jni.h>
#include <string.h>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_m_ndktest_MainActivity_testJNI(JNIEnv *env, jobject instance)
{
    return env->NewStringUTF(hello.c_str());

}

JNIEXPORT jstring JNICALL
Java_com_example_m_ndktest_MainActivity_testJNI2(JNIEnv *env, jobject instance)
{
    return (*env)->NewStringUTF(env, "hellooooo");

}

我应该如何将我的 .mk 文件包含在 CMakeLists.txt 中？

CMakeLists.txt:

# 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)

# 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).
             src/main/cpp/native-lib.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

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

***Also I have a question, where can I find the tutorial about the STRANGE syntax that we should write in Android-ndk? (I mean the test.c syntax that I copied from the default native-lib.c)

Answer 1

Android Studio 有外部原生构建的概念。对于这些外部 native 构建，您有 two选项:

• ndk 构建
• CMake

CMake 似乎是更现代的，因此可能更适合 future 。我建议使用那个。

这意味着您编写了一个 CMakeLists.txt 文件(通常在您的 jni/ 目录中。)

您不再需要任何 .mk 文件，它们由 ndk-build 外部原生构建使用，而不是 CMake 构建。

要指示您使用的是哪个外部 native 构建系统，您可以使用应用的 gradle 文件。

android {
    defaultConfig {
        externalNativeBuild {
            cmake {
                cppFlags "..."
                arguments "..."
            }
        }
    }
}

在 CMakeLists.txt 文件中，您描述了如何构建原生 .so 库。这包括列出构建它所需的所有 .c 和 .cpp 源文件。这是通过 CMake 的 add_library() 完成的。宏。

总而言之，您的新项目定义将包含 gradle 文件和一个(或多个)CMakeLists.txt 文件，但您不再需要任何 .mk 文件。