©2020-2024 ioDraw All rights reserved,
Privacy Policy
本博客只是搭建了jni编程所需要的环境，通过一个简单的例子展示了其流程，用于以后参考查阅，不涉及jni的复杂内容。
<>一、环境搭建
除了Android开发所需要的环境外还需要cmake、ndk。
1、现在sdk manager中安装cmake、ndk
2、在local.propertites中设置ndk路径ndk.dir=E\:\\DevTools\\Sdk\\ndk\\24.0.8215888
，其路径会自动同步到project structure中。
<>二、jni示例
1、在MainActivity同级目录下创建Java类
package com.example.myapplication1; public class JniHello{ static { System.
loadLibrary("JniHello"); } public static native String welcomeJniStudy(); }
2、创建javah和ndk通用工具
首先选择File->Settings->Tools->External Tools创建javah工具，其具体设置如下：
Program: E:\DevTools\Java\jdk1.8.0_162\bin\javah.exe
Arguments: -classpath . -jni -d
E:\TestProjects\MyApplication1\app\src\main\jni $FileClass$
Working directory: E:\TestProjects\MyApplication1\app\src\main\java
然后创建ndk-build工具，具体设置如下：
Program:E:\DevTools\Sdk\ndk\24.0.8215888\build\ndk-build.cmd //安装ndk的路径
Arguments:
Working directory:E:\TestProjects\MyApplication1\app\src\main
3、通过通用工具javah生成C头文件
就会在jni文件夹下生成相应的c头文件
4、创建Android.mk和Application.mk
//Android.mk LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_LDLIBS
+= -llog LOCAL_LDLIBS +=-lm LOCAL_MODULE := JniHello LOCAL_SRC_FILES =:
JniHello.cpp # 实现c代码文件的名字 include $(BUILD_SHARED_LIBRARY) //Application.mk
APP_MODULES := JniHello APP_ABI := all
5、实现c头文件中的方法，文件命名为JniHello.cpp
文件内容为：
#include "com_example_myapplication1_JniHello.h" JNIEXPORT jstring JNICALL
Java_com_example_myapplication1_JniHello_welcomeJniStudy(JNIEnv *env, jclass
jclass){ return env->NewStringUTF("welcome to study jni"); }
6、修改app下的build.gradle，在defaultConfig中添加如下内容
ndk{ moduleName "JniHello" //abiFilters \"armeabi-v7a", "x86" //输出指定abi下的so库 }
sourceSets.main { jni.srcDirs = [] jniLibs.srcDir "src/main/libs" }
7、生成so文件
就会在libs文件夹下生成相应的so文件
8、在MainActivity.java中调用测试
public class MainActivity extends AppCompatActivity { @Override protected void
onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); String str=new JniHello().
welcomeJniStudy(); System.out.println("============="+str); } }
输出结果
05/06 18:33:35: Launching 'app' on Nexus 5 API 29. Install successfully
finished in 979 ms. $ adb shell am start -n
"com.example.myapplication1/com.example.myapplication1.MainActivity" -a
android.intent.action.MAIN -c android.intent.category.LAUNCHER Connected to
process 16900 on device 'Nexus_5_API_29 [emulator-5554]'. Capturing and
displaying logcat messages from application. This behavior can be disabled in
the "Logcat output" section of the "Debugger" settings page. D/libEGL: Emulator
has host GPU support, qemu.gles is set to 1. W/libc: Unable to set property
"qemu.gles" to "1": connection failed; errno=13 (Permission denied)
W/RenderThread: type=1400 audit(0.0:35): avc: denied { write } for
name="property_service" dev="tmpfs" ino=7421
scontext=u:r:untrusted_app:s0:c134,c256,c512,c768
tcontext=u:object_r:property_socket:s0 tclass=sock_file permissive=0 D/libEGL:
loaded /vendor/lib/egl/libEGL_emulation.so D/libEGL: loaded
/vendor/lib/egl/libGLESv1_CM_emulation.so D/libEGL: loaded
/vendor/lib/egl/libGLESv2_emulation.so W/.myapplication: Accessing hidden
method
Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z
(greylist, reflection, allowed) Accessing hidden method
Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist,
reflection, allowed) I/System.out: =============welcome to study jni
D/HostConnection: HostConnection::get() New Host Connection established
0xd89bac30, tid 16931 D/HostConnection: HostComposition ext
ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2