Android基础6--NDK编程1

Android项目中创建Library模块

步骤：项目名称右键->New->Moudle->Android Library

编译：

编译单独模块：选中模块->Build->Make Moudle

旧版本产出位置：模块\build\intermediates\packaged-classed\debug\

新版本产出位置：模块\build\intermediates\arr_main_jar\debug\

使用Android SDK中的dx工具生成

dx位置：AndroidSDK根目录\build-tools\28.0.3\dx.bat

用法：dx.bat–dex–output=xx srcDir

set filename=test2.jar
set srcDir=D:\__job\study20230717-pkgJar\pkgJarForLoad\mylibrary1\build\intermediates\aar_main_jar\debug\
set dx="D:\Android SDK\build-tools\34.0.0\d8.bat"
del  out\%filename%
call %dx% --dex --output=out\%filename%  %srcDir%
pause

使用gradlew生成

模块内build.gradle添加：

task makeJar(type:Copy)

{

//删除旧的jar

delete 'build/libs/test.jar'

//设置源.jar目录

from('build/intermediates/arr_main_jar/release')

//设置产出目录

into('build/libs/')

//设置源目录内文件过滤

include('classes.jar')

//重命名

rename('classes.jar','test.jar)

}

项目根目录执行Ctrl+Enter:

gradlew makeJar

NDK编程

创建NDK项目及JNI函数

创建NDK项目：

1、下载ndk

2、创建so项目

NDK（Native Development Kit）是Android提供的一个工具集，允许开发者使用C或C++等本地语言编写部分Android应用的代码，并通过JNI（Java Native Interface）与Java代码进行交互。NDK主要用于提高应用程序的性能、复用现有的本地代码库以及访问设备硬件等功能

创建JNI函数

1、函数命名规则

2、参数

JNI（Java Native Interface）是Java提供的一种机制，用于实现Java代码与本地（Native）代码（如C、C++等）之间的交互和通信。它允许Java应用程序调用本地方法（Native Method），也允许本地方法调用Java代码。

函数签名

作用：函数的身份证

方法：javap -s a.b.cjavareflection.Student获取签名

例子( descriptor: (Ljava/lang/String;DJ)I)

读写SD卡文件

权限：静态申请权限、动态申请权限、检查自己权限

读取文件：fopen、fgets、fput、fclose

MainActivity

package a.b.c.ndk01;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import androidx.core.content.PackageManagerCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import a.b.c.ndk01.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity
{

    private final static int MY_PERMISSIONS_REQUEST_WRITE_CODE = 11;
    // Used to load the 'ndk01' library on application startup.
    static {
        System.loadLibrary("ndk01");
    }
    public int testFun(String a,Double b,long c)
    {
        return 1;
    }


    private ActivityMainBinding binding;

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults)
    {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch(requestCode)
        {
            case MY_PERMISSIONS_REQUEST_WRITE_CODE:
            {
                if(grantResults.length>0 && grantResults[0]!=-1)
                {
                    Log.i("qqqqqq","写SDCard权限申请成功");
                }
                else
                {
                    Log.i("qqqqqq","写SDCard权限申请失败");
                }
                break;
            }
            case 33:
            {
                Log.i("qqqqqq","这里是申请其他权限的结果");
                break;
            }
        }


    }

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());
        testFun("aa",4.5,5);

        // Example of a call to a native method
        TextView tv = binding.sampleText;
        tv.setText(stringFromJNI());
        tv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view)
            {
                int ret = ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE);// ContextCompat这里选Android
                if(ret == PackageManager.PERMISSION_GRANTED)
                {
                    Log.i("qqqqqq","已经有写SDCar的权限");
                    String fp1 = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();
                    String fc = readSDcardFile(fp1+"b.txt");
                    Log.i("qqqqqq","文件内容" + fc);
                }
                else
                {
                    Log.i("qqqqqq","还没有写SDCar的权限");
                    ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},MY_PERMISSIONS_REQUEST_WRITE_CODE);
                }
            }
        });
    }

    /**
     * A native method that is implemented by the 'ndk01' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();
    public native int getlength(String param);
    public native String readSDcardFile(String filepath);
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>
    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.Ndk01"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

jni.h

extern "C"
JNIEXPORT jstring JNICALL
Java_a_b_c_ndk01_MainActivity_readSDcardFile(JNIEnv *env, jobject thiz, jstring filepath) ;
    // TODO: implement readSDcardFile()

native-lib.cpp

extern "C"
JNIEXPORT jstring JNICALL
Java_a_b_c_ndk01_MainActivity_readSDcardFile(JNIEnv *env, jobject thiz, jstring filepath)
{
    char* filePath = (char*)env->GetStringUTFChars(filepath,0);
    FILE *fp;
    jstring jstring_ret = env->NewStringUTF("null");
    char *tmp = (char*)env->GetStringUTFChars(jstring_ret,0);
    fp = fopen(filePath,"r");//"r"：只读模式，文件必须存在。
    if(fp == NULL)
    {
        LOGE("fp == NULL, %s",filePath);
        return jstring_ret;
    }
    char buff[1024];
    while(fgets(buff,1024,fp)!=NULL)
    {
        LOGI("fgets :%s",buff)
    }
    env->ReleaseStringChars(jstring_ret,reinterpret_cast<const jchar*>(tmp));
    jstring_ret = env->NewStringUTF(buff);
}

JNI 签名规则

在JNI中，方法签名采用一种特定的格式，用于描述Java方法的参数类型和返回值类型。格式为：

• 参数类型：
  • Z：boolean
  • B：byte
  • C：char
  • S：short
  • I：int
  • J：long
  • F：float
  • D：double
  • Lfully/qualified/ClassName;：对象类型，如 Ljava/lang/String;
  • [Type：数组类型，如 [I 表示 int[]
  • ( 和 )：分别用于标识方法的开始和结束

Java反射

作用：获取和操作已经装载的类。

函数：

1、获取类：

1.1Class.forName(“类名全路径”) 1.2类名.class c 1.3实例.getClass()

2、获取方法和属性：

2.1 类.getDeclareMethods() 2.2类.getDeclaredConstructors() 2.3类.getMethod() 2.4类.getDeclaredFields()

public void fun2()
{
    Class clz = Student.class;

    try
    {
        Method method_study = clz.getMethod("study",new Class[]{int.class});
        Constructor constructor_Student = clz.getConstructor(new Class[]{String.class,int.class});
        Student student = (Student) constructor_Student.newInstance(new Object[]{"lisi",25});
        Object obj_ret = method_study.invoke(student,new Object[]{77});
        Log.i("qqqqqqqq","study ret:" + (String) obj_ret);
    }catch (Exception ee)
    {
        ee.printStackTrace();

3、调用方法:

3.1方法.invoke()

public void fun3()
{
    Class clz = one.getClass();
    try
    {
        Method method_getAge0 = clz.getDeclaredMethod("getAge");
        method_getAge0.setAccessible(true);
        Method method_getAge = clz.getMethod("getAge",new Class[]{});
        Object obj_ret = method_getAge.invoke(one,new Object[]{});
        Log.i("qqqqqqq","getAge ret"+(int)obj_ret);
    }catch (Exception ee)
    {
        ee.printStackTrace();
    }
}

NDK反射Java层

作用：NDK层代码可以获取、调用java层方法和变量

函数：

1、获取类：

1.1jclass GetObjectClass(对象) 1.2jclass FindClass(“类名”)

2、获取方法ID:(javap -s a.b.c.javareflectiontest.Student获取签名)

2.1jmetthodID GetMethodID(jclass,const char*name,const char(sig))

2.2jmethodID GetstaticMethodID(jclass clazz,const char*name,const char(sig))

3、调用方法：

3.1void CallVoidMethod(jobject obj,jmethodID,methodID,…)

3.2void CallStaticVoidMethod(jclass clazz,jmethodID,methodID,….)

3.3jobject CallObjectMethod(JNEnv*,jobject,jmethodID,….)

4、获取和设置成员变量

4.1GetFieldID

4.2GetObjectField

4.3SetObjectField

extern "C"
JNIEXPORT jstring JNICALL
Java_a_b_c_ndk01_MainActivity_callStaticJavaFunJNI(JNIEnv *env, jobject thiz)
{
    jclass jclass_student2 = env->FindClass("a/b/c/ndk01/Student");
    jmethodID jmethodId_calcLength = env->GetStaticMethodID(jclass_student2,"calcLength", "(Ljava/lang/String;)I");
    jstring jstring_param = env->NewStringUTF("hahahaha");
    jint jint_ret = env->CallStaticIntMethod(jclass_student2,jmethodId_calcLength,jstring_param);
    LOGI("ndk call calcLength ret: %d",jint_ret);
    return jstring_param;
}