gradle3.0以上进行jni调用的时候和之前的版本会略有不同
首先第一步:
首先新建一个工程, 我的工程目录如下:
我本地使用的gradle版本:
app的build.gradle内容如下所示:
android {
apply plugin: 'com.android.application'
android {
compileSdkVersion 27
defaultConfig {
applicationId "com.jni.jnidemo5"
minSdkVersion 26
targetSdkVersion 27
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:27.0.2'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}
以上就是新建的工程的基本设置, 接下来就是正式开始:
首先在包下新建一个JNINative.java的类用于写native方法
package com.jni.jnidemo5;
public class JNINative {
public native String getString();
}
很简单只有一个获取字符串的方法.
使用javah生成对应的.h文件
具体方法如下:
打开Android Studio的Terminal(控制台)
输入: cd app/src/main/java
输入: javah com.jni.jnidemo5.JNINative
会在工程的 app/src/main/java/下生成对应的.h文件
生成的.h文件内容如下:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_jni_jnidemo5_JNINative */
#ifndef _Included_com_jni_jnidemo5_JNINative
#define _Included_com_jni_jnidemo5_JNINative
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_jni_jnidemo5_JNINative
* Method: getString
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_jni_jnidemo5_JNINative_getString
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
编写对应的C文件
在src上右键新建一个jni目录, 目录结构如下
在jni目录下右键 新建一个hellotest.c文件
文件的内容如下(根据生成的.h文件修改而成):
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_jni_jnidemo5_JNINative */
#ifndef _Included_com_jni_jnidemo5_JNINative
#define _Included_com_jni_jnidemo5_JNINative
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_jni_jnidemo5_JNINative
* Method: getString
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_jni_jnidemo5_JNINative_getString
(JNIEnv *env, jclass jobject){
return (*env)->NewStringUTF(env,"hello world from c!!!");
}
#ifdef __cplusplus
}
#endif
#endif
注意这里修改的内容:
配置NDK环境
点击project structure 设置工程的ndk目录
接下来是和低版本的gradle不一致的地方了, 因为gradle3.0以上useDeprecatedNdk这个东西不推荐使用了, 也就是我们不需要在gradle.properties里添加android.useDeprecatedNdk=true这句话了
如果我们还使用这个东东, studio就会提示我们:
Error:Execution failed for task ':app:compileDebugNdk'. > Error: Flag android.useDeprecatedNdk is no longer supported and will be removed in the next version of Android Studio. Please switch to a supported build system.Consider using CMake or ndk-build integration.
推荐我们使用CMake, 这里我就选择CMake方式
CMake方式实现编译so文件
- 打开SDK Manager
勾选箭头指向的两个插件, 安装
2.在app的build.gradle里的deaultConfig节点里添加如下代码:
externalNativeBuild {
cmake {
cppFlags ""
//生成多个版本的so文件
abiFilters 'arm64-v8a','armeabi-v7a','x86','x86_64'
}
}
如下图所示:
3.在android节点里添加如下代码
externalNativeBuild {
cmake {
path "CMakeLists.txt" // 该文件配置了c源码位置,以及编译后so文件的名字
}
}
如下图所示
4.在和app里的build.gradle的同级目录里新建一个名为CMakeLists.txt的文件, 并copy如下代码
# 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.
#CMakeLists.txt
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.
# 设置so文件名称.
hello
# Sets the library as a shared library.
SHARED
# 设置这个so文件为共享.
# Provides a relative path to your source file(s).
# 设置我们的c/c++文件路径, 注意文件名要和我们的c文件相同
src/main/jni/hellotest.c)
# 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.
# 制定目标库.注意要和上面的so文件名称一致
hello
# Links the target library to the log library
# included in the NDK.
${log-lib} )
注意自己要修改里面带注释的地方, 主要是c文件名和编译后的so的文件名
5.然后Build工程我们就能看到编译成功的so库文件了, 如下所是:
6.Copy生成的so文件到lib目录下:
7.修改MainActivity里的代码让我们的程序跑起来
package com.jni.jnidemo5;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private TextView tv;
static {
System.loadLibrary("hello");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = findViewById(R.id.tv);
tv.setText(new JNINative().getString());
}
}
点击run运行结果如下:
demo下载地址: