修改android ndk 修改Android id有什么用处

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mob64ca14017c37 2023-12-09 23:10:29

文章标签 修改android ndk #define Android so库 文章分类 Android 移动开发

1、NDK 是一组允许您将 C 或 C++（“原生代码”）嵌入到 Android 应用中的工具。

2、好处：

①在平台之间移植其应用。
②重复使用现有库，或者提供其自己的库供重复使用。
③在某些情况下提高性能，特别是像游戏这种计算密集型应用。

3、怎么使用？

现在要做的是从jni中把数据返回，在java中把数据显示。

开发环境是AndroidStudio,先把NDK的环境配置好。

在项目目录下的gradle.properties文件中，添加NDK支持，

android.useDeprecatedNdk=true

然后在app目录下的build.gradle文件中写入生成so库的名字和输入指定的平台。

ndk{
            moduleName "hello-jni"       //生成的so文件名字，调用C程序的代码中会用到该名字
            abiFilters "armeabi", "armeabi-v7a", "x86" //输出指定三种平台下的so库
        }

具体放在：

defaultConfig {
        applicationId "com.example.hellojni"
        minSdkVersion 15
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        ndk{
            moduleName "hello-jni"       //生成的so文件名字，调用C程序的代码中会用到该名字
            abiFilters "armeabi", "armeabi-v7a", "x86" //输出指定三种平台下的so库
        }
    }

到此为，NDK的环境已经配置好了。

使用：

在main目录下，建一个jni文件夹，把以下三个文件复制进去，Android.mk,Application.mk,hello-jni.c

修改android ndk 修改Android id有什么用处_Android

Android.mk:

# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
LOCAL_PATH := $(call my-dir)#此变量表示源文件在开发树中的位置。在这里，构建系统提供的宏函数 my-dir 将返回当前目录（包含 Android.mk 文件本身的目录）的路径。

include $(CLEAR_VARS)#CLEAR_VARS 变量指向特殊 GNU Makefile，可为您清除许多 LOCAL_XXX 变量，例如 LOCAL_MODULE、LOCAL_SRC_FILES 和 LOCAL_STATIC_LIBRARIES。 请注意，它不会清除 LOCAL_PATH。此变量必须保留其值，因为系统在单一 GNU Make 执行环境（其中所有变量都是全局的）中解析所有构建控制文件。 在描述每个模块之前，必须声明（重新声明）此变量。

LOCAL_MODULE    := hello-jni#LOCAL_MODULE 变量将存储您要构建的模块的名称.生成一个名为 libhello-jni.so 的库。
LOCAL_SRC_FILES := hello-jni.c#LOCAL_SRC_FILES 变量必须包含要构建到模块中的 C 和/或 C++ 源文件列表。

include $(BUILD_SHARED_LIBRARY)#帮助系统将所有内容连接到一起.BUILD_SHARED_LIBRARY 变量指向 GNU Makefile 脚本，用于收集您自最近 include 后在 LOCAL_XXX 变量中定义的所有信息。 此脚本确定要构建的内容及其操作方法。

Application.mk:

APP_ABI := all
#Application.mk 文件实际上是定义要编译的多个变量的微小 GNU Makefile 片段。
#它不会实际进入生成的共享库或最终软件包。APP_ABI := all指的是所有支持的指令集。
#也可以指定多个值，将它们放在同一行上，中间用空格分隔。例如：
#APP_ABI := armeabi armeabi-v7a x86 mips

hello-jni.c:

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
#include <string.h>
#include <jni.h>

/* This is a trivial JNI example where we use a native method
 * to return a new VM String. See the corresponding Java source
 * file located at:
 *
 *   apps/samples/hello-jni/project/src/com/example/hellojni/HelloJni.java
 */
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
                                                  jobject thiz )
{
#if defined(__arm__)
  #if defined(__ARM_ARCH_7A__)
    #if defined(__ARM_NEON__)
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a/NEON (hard-float)"
      #else
        #define ABI "armeabi-v7a/NEON"
      #endif
    #else
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a (hard-float)"
      #else
        #define ABI "armeabi-v7a"
      #endif
    #endif
  #else
   #define ABI "armeabi"
  #endif
#elif defined(__i386__)
   #define ABI "x86"
#elif defined(__x86_64__)
   #define ABI "x86_64"
#elif defined(__mips64)  /* mips64el-* toolchain defines __mips__ too */
   #define ABI "mips64"
#elif defined(__mips__)
   #define ABI "mips"
#elif defined(__aarch64__)
   #define ABI "arm64-v8a"
#else
   #define ABI "unknown"
#endif

    return (*env)->NewStringUTF(env, "Hello from JNI !  Compiled with ABI " ABI ".");
}

新建一个HelloJni的类：

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.hellojni;

import android.app.Activity;
import android.widget.TextView;
import android.os.Bundle;


public class HelloJni extends Activity
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        /* Create a TextView and set its content.
         * the text is retrieved by calling a native
         * function.
         */
        TextView  tv = new TextView(this);
        tv.setText( stringFromJNI() );
        setContentView(tv);
    }

    /* A native method that is implemented by the
     * 'hello-jni' native library, which is packaged
     * with this application.
     */
    public native String  stringFromJNI();

    /* This is another native method declaration that is *not*
     * implemented by 'hello-jni'. This is simply to show that
     * you can declare as many native methods in your Java code
     * as you want, their implementation is searched in the
     * currently loaded native libraries only the first time
     * you call them.
     *
     * Trying to call this function will result in a
     * java.lang.UnsatisfiedLinkError exception !
     */
    public native String  unimplementedStringFromJNI();

    /* this is used to load the 'hello-jni' library on application
     * startup. The library has already been unpacked into
     * /data/data/com.example.hellojni/lib/libhello-jni.so at
     * installation time by the package manager.
     */
    static {
        System.loadLibrary("hello-jni");
    }
}

ps:注意，包名是com.example.hellojni，如果你的包名不是这个的，可以改hello-jni.c文件中的Java_com_example_hellojni_HelloJni_stringFromJNI。要不然会找不到生成的so库。比如说你的包名是com.xxx.xxx。那改成Java_com_xxx.xxx_hellojni_HelloJni_stringFromJNI

System.loadLibrary("hello-jni");//"hello-jni"是so库的名字。

在这里可以看到生成的so库：

修改android ndk 修改Android id有什么用处_Android_02