C++文件中打印log
从android studio3.0开始，使用cmake文件编译生成so文件，首先需要在打开的项目中，从菜单栏选择 Tools > Android > SDK Manager。
点击 SDK Tools 标签。
选中 LLDB、CMake 和 NDK 旁的复选框
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我们在创建工程初始，需要勾选，选中 Include C++ Support 复选框，创建完成以后，目录结构如下：
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CMAKEList配置
在CMAKEList配置ndk生成的so文件名称，以及打印log的配置，AS已经默认帮我们配置好了，内容如下：
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} )
配置log打印
c++中添加log打印，内容固定，添加下面代码即可：
#include <android/log.h>
#define LOG_TAG "native-dev"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
LOGE("liuhang test");
完整代码如下：
#include <jni.h>
#include <string>
#include <android/log.h>
#define LOG_TAG "native-dev"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
extern "C"
JNIEXPORT jstring JNICALL
Java_com_jni_test_MainActivity_stringFromJNI(
JNIEnv* env,
jobject /* this */) {
std::string hello = "Hello from C++";
LOGE("liuhang test");
return env->NewStringUTF(hello.c_str());
}
打印如下：
image.png
使用cmake生成多个so文件
我们可以针对多个cpp文件生成同一个so，同样的，也可以生成多个so文件，如下步骤：
- 针对不同so文件，建立不同的目录，每个目录下由单独的CMakeLists.txt文件
- 在外层的CMakeLists.txt中，通过ADD_SUBDIRECTORY添加不同的目录配置
AS会首先通过ADD_SUBDIRECTORY找到对应的目录，在在对应目录的CMakeLists.txt文件内容，生成对应的so文件，对应的目录结构如下：
image.png
建立DataProvider类
package com.jni.test;
/**
* Created by liuhang on 18-7-15.
*/
public class DataProvider {
/**
* 把java中的int传递给c语言，c语言处理完毕后，把结果相加返回给java
* @param x
* @param y
* @return
*/
public static native int add(int x, int y);
static {
System.loadLibrary("test-lib");
}
}
first目录下对应的CMakeLists.txt
cmake_minimum_required(VERSION 3.4.1)
#生成so动态库
ADD_LIBRARY(native-lib SHARED native-lib.cpp)
target_link_libraries(native-lib log)
second目录下对应的CMakeLists.txt
cmake_minimum_required(VERSION 3.4.1)
#生成so动态库
ADD_LIBRARY(test-lib SHARED test-lib.cpp)
target_link_libraries(test-lib log)
对应的test-lib.cpp
#include <jni.h>
#include <string>
#include <android/log.h>
#define LOG_TAG "liuhang"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
extern "C"
/*
* Class: com_jni_test_DataProvider
* Method: add
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_com_jni_test_DataProvider_add
(JNIEnv * env, jobject obj, jint x, jint y) {
LOGI("x is : %d", x);
LOGI("y is : %d", y);
return x + y;
}
外层CMakeLists.txt
cmake_minimum_required(VERSION 3.4.1)
#添加子目录,将会调用子目录中的CMakeLists.txt
ADD_SUBDIRECTORY(first)
ADD_SUBDIRECTORY(second)
在app/build.gradle配置外层CMakeLists.txt
apply plugin: 'com.android.application'
android {
compileSdkVersion 25
buildToolsVersion "27.0.3"
defaultConfig {
applicationId "com.jni.test"
minSdkVersion 21
targetSdkVersion 27
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags "-frtti -fexceptions"
abiFilters "armeabi", "armeabi-v7a", "x86"
}
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "src/main/cpp/CMakeLists.txt" #配置外层CMakeLists.txt路径
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:25.3.1'
testCompile 'junit:junit:4.12'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
}
上述externalNativeBuild标签为ndk相关配置
上述配置已经完成，(别忘了使用的使用，通过native声明本地方法，以及通过loadlibrary来加载so文件)，现在编译该模块，菜单键选择如下：build --> make project,,默认生成的so文件路径在build目录下，如下：
image.png
