android基础巩固之ndk

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环境配置

为了工程不出现问题最好是新建项目的时候选择c++/c项目支持 (android studio创建项目)##

app/library module gradle 配置

apply plugin: 'com.android.library'

android {
    defaultConfig {
       externalNativeBuild {
           cmake {
               cppFlags ""
           }
       }

       ndk {
           ldLibs "log"//实现__android_log_print
           abiFilters  'x86', 'armeabi-v7a'
       }

    }

    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
        }
    }

}

src/main/cpp/CMakeList.txt 项目创建的时候会自动生成，如果没有从其它地方复制 , main/cpp目录不存在就自己创建

cmake_minimum_required(VERSION 3.4.1)

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).
             native-lib.cpp
        )

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 )


target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

native-lib.cpp 选择cpp是因为了解这块,各选语言###

#include <jni.h>
#include <stdlib.h>
#include <string>
#include <iostream>
#include <android/log.h>

using namespace std;

#define  LOG_TAG    "zzg-ndk"
#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 LOGD(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)

extern "C"
JNIEXPORT jboolean JNICALL
Java_com_example_zyframework_SDKApi_isExpired(JNIEnv *env, jobject jobj, jlong time) {

    LOGE("native isExpret time = %lld ", time);
    return (jboolean) b;
}

使用示例

1.数据传递

• java传递数据给c(包含对象)
• c传递数据给java(包含对象)

2.c调用java成员变量\方法\创建java层对象

3. static native 使用示例

3. static native 静态的native方法

c代码中调用java中的方法示例

java代码

public class SDKUtils {
    public void setTag(String tag) {
        Log.e("zzg-ndk", "setTag tag = " + tag);
    }

    public static native void updateTag(String key);
}

cpp代码

extern "C"
JNIEXPORT void JNICALL
Java_com_example_sdkjiagu_SDKUtils_updateTag(JNIEnv *env, jclass jcls, jstring key_) {
    const char *key = env->GetStringUTFChars(key_, 0);
    LOGE("native updateTag key = %s ", key);
    env->ReleaseStringUTFChars(key_, key);
    // 得到jobject不会走构造方法
    jobject jobj = (*env).AllocObject(jcls);
    jmethodID _mid = (*env).GetMethodID(jcls, "setTag", "(Ljava/lang/String;)V");

    string t_new = "2019-01-18 23:59:59";
    (*env).CallVoidMethod(jobj,_mid,env->NewStringUTF(t_new.c_str()));
}

辅助资料

ndk编译之后so的路径

F:\zyprojectspace\AsProjects\zzgapps\HelloNdkCpp\ZYFramework\build\intermediates\cmake\debug\obj\x86

方法的方法签名的查看

未完，待续