android基礎鞏固之ndk

摘要： 環境配置 為了工程不出現問題最好是新建專案的時候選擇c++/c專案支援 (android studio建立專案) app/library module gradle 配置 apply plugin: 'com.android.library' an...

環境配置

為了工程不出現問題最好是新建專案的時候選擇c++/c專案支援 (android studio建立專案)

app/library module gradle 配置

apply plugin: 'com.android.library'

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

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

}

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

}

src/main/cpp/CMakeList.txt 專案建立的時候會自動生成，如果沒有從其它地方複製 , main/cpp目錄不存在就自己建立

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 選擇cpp是因為了解這塊,各選語言###

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

using namespace std;

#defineLOG_TAG"zzg-ndk"
#defineLOGI(...)__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.資料傳遞

• java傳遞資料給c(包含物件)
• c傳遞資料給java(包含物件)

java傳遞資料給c,c返回資料給java(包含物件)

java程式碼

static {
System.loadLibrary("native-lib");
}

private Stringtag = "zzg-ndk";

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

// Example of a call to a native method
TextView tv = findViewById(R.id.sample_text);
tv.setText(stringFromJNI());

SimpleDateFormat simpleDateFormat = new SimpleDateFormat
("yyyy-MM-dd HH:mm:ss");
String dateStr = simpleDateFormat.format(new Date());
sayHello(dateStr);

int addV = add(12, 5);
Log.e(tag, "c add result = " + addV);

float f = getFloat(3.1415926f);
Log.e(tag, "c getFloat result = " + f);

double d = getDouble(35.0);
Log.e(tag, "c getDouble result = " + d);

boolean b = getBoolean(true);
Log.e(tag, "c getBoolean result = " + b);

String s = getString("開啟電視");
Log.e(tag, "c getString result = " + s);

long l = getLong(3500l);
Log.e(tag, "c getDouble result = " + l);

String[] n_arr = getStringArray(new String[]{"上海", "天津", "濟南"});
for (String s_t : n_arr) {
Log.e(tag, s_t);
}

/**
* 在c層進行物件的轉換
*/
ResultInfo resultInfo = new ResultInfo("2018-12-22", 39);
Log.e(tag, "resultInfo = " + resultInfo);
WeatherInfo weatherInfo = convertInfo(resultInfo);
if (weatherInfo != null) {
Log.e(tag, "weatherInfo = " + weatherInfo);
}
}

public native String stringFromJNI();
private native void sayHello(String str);
private native int add(int a, int b);
private native float getFloat(float f);
private native double getDouble(double d);

private native boolean getBoolean(boolean b);
private native String getString(String str);
private native long getLong(long l);
private native String[] getStringArray(String[] sa);
/**
 * 物件轉換
 */
private native WeatherInfo convertInfo(ResultInfo info);

cpp程式碼

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

using namespace std;

#defineLOG_TAG"zzg-ndk"
#defineLOGI(...)__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 jstring JNICALL
Java_com_example_hncpp_MainActivity_stringFromJNI(
JNIEnv *env,
jobject /* this */) {
std::string hello = "Hello from C++";
jstring sr = env->NewStringUTF(hello.c_str());
const char *locstr = env->GetStringUTFChars(sr, 0);
LOGE("stringFromJNI locstr = %s", locstr);
env->ReleaseStringUTFChars(sr, locstr);
return sr;
}

extern "C"
JNIEXPORT void JNICALL
Java_com_example_hncpp_MainActivity_sayHello(JNIEnv *env, jobject obj, jstring str_) {
const char *str = env->GetStringUTFChars(str_, 0);
env->ReleaseStringUTFChars(str_, str);
LOGE("sayHello str = %s", str);
}

extern "C"
JNIEXPORT jint JNICALL
Java_com_example_hncpp_MainActivity_add(JNIEnv *env, jobject obj, jint a, jint b) {
int i = a;
int j = b;
LOGE("add 接收到的java 資料：a =%d , b =%d", a, b);
LOGE("add 轉換之後c的資料：i = %d , j = %d", i, j);
return i + j;
}

extern "C"
JNIEXPORT jfloat JNICALL
Java_com_example_hncpp_MainActivity_getFloat(JNIEnv *env, jobject obj, jfloat f) {
float f_l = f;
LOGE("getFloat 接收到的java 資料：f = %3f ", f);
LOGE("getFloat 轉換之後c的資料：f_l = %3f", f_l);
f_l = f_l * 0.2f;
LOGE("getFloat 計算之後的資料：f_l = %3f", f_l);
return (jfloat) f_l;
}

extern "C"
JNIEXPORT jdouble JNICALL
Java_com_example_hncpp_MainActivity_getDouble(JNIEnv *env, jobject obj, jdouble d) {
double d_1 = d;
LOGE("getDouble 接收到的java 資料：d = %1f ", d);
LOGE("getDouble 轉換之後c的資料：d_l = %1f", d_1);
d_1 = 3 * d_1;
LOGE("getFloat 計算之後的資料：d_1 = %1f", d_1);
return (jdouble) d_1;
}


extern "C"
JNIEXPORT jboolean JNICALL
Java_com_example_hncpp_MainActivity_getBoolean(JNIEnv *env, jobject obj, jboolean b) {
unsigned char b_1 = b;
LOGE("getDouble 接收到的java 資料：d = %lu", b_1);
if (b_1) {
LOGE("true");
} else {
LOGE("false");
}
return !b_1;
}

//
extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_hncpp_MainActivity_getString(JNIEnv *env, jobject obj, jstring str_) {
const char *str = env->GetStringUTFChars(str_, 0);
//LOGE("getDouble 接收到的java 資料：str = %s", str);
//std::string hello = "收到指令，準備進行操作, 操作成功";
//env->ReleaseStringUTFChars(str_, str);
//return env->NewStringUTF(hello.c_str());

//字串拼接
//string str = "Dream a Dream";
//str.insert(str.length()," i have");
//str.insert(0, " i have ");

//字串拼接
string tmp_s_1 = "收到指令 ", tmp_s_2 = " , 準備進行操作, 操作成功";
tmp_s_1.insert(tmp_s_1.length(), str);
tmp_s_1.insert(tmp_s_1.length(), tmp_s_2);
env->ReleaseStringUTFChars(str_, str);
return env->NewStringUTF(tmp_s_1.c_str());
}



extern "C"
JNIEXPORT jlong JNICALL
Java_com_example_hncpp_MainActivity_getLong(JNIEnv *env, jobject obj, jlong l) {
long l_1 = l;
LOGE("getDouble 接收到的java 資料：l = %ld ", l);
LOGE("getDouble 轉換之後c的資料：l_1 = %ld", l_1);
l_1 = 1.5f * l_1;
LOGE("getFloat 計算之後的資料：l_1 = %ld", l_1);
return (jlong) l_1;
}

extern "C"
JNIEXPORT jobjectArray JNICALL
Java_com_example_hncpp_MainActivity_getStringArray(JNIEnv *env, jobject obj, jobjectArray sa) {
int len = (*env).GetArrayLength(sa);
int i = 0;
// 獲取資料型別
jclass objCls = env->FindClass("java/lang/String");
// 生成新的陣列
jobjectArray jarr = (*env).NewObjectArray(len, objCls, 0);
for (i = 0; i < len; i++) {
jobject jobj = (*env).GetObjectArrayElement(sa, i);
jstring str = static_cast<jstring>(jobj);
const char *szStr = (*env).GetStringUTFChars(str, 0);
LOGE("arr[%d] = %s ", i, szStr);
env->ReleaseStringUTFChars(str, szStr);
//拼接資料
string t_new = "new_";
t_new.insert(t_new.length(), szStr);
env->SetObjectArrayElement(jarr, i, env->NewStringUTF(t_new.c_str()));
}
return jarr;
}

//物件轉換
extern "C"
JNIEXPORT jobject JNICALL
Java_com_example_hncpp_MainActivity_convertInfo(JNIEnv *env, jobject jobj, jobject rInfo) {
// 獲取傳入的物件的值
jclass r_info_jcls = (*env).GetObjectClass(rInfo);
// 這裡通過反射的方式取欄位的值
jfieldID r_info_date_jfid = (*env).GetFieldID(r_info_jcls, "date", "Ljava/lang/String;");
// 取date值
jobject r_info_date_jobj = (*env).GetObjectField(rInfo, r_info_date_jfid);
// 這裡是java字串
jstring r_info_date_jstr = static_cast<jstring>(r_info_date_jobj);
const char *r_info_date_cstr = (*env).GetStringUTFChars(r_info_date_jstr, 0);
// 釋放資源
(*env).ReleaseStringUTFChars(r_info_date_jstr, r_info_date_cstr);
LOGE("ndk ->ndk -> date = %s", r_info_date_cstr);

// 這裡通過呼叫方法取到tmp值
jmethodID jmid_rinfo_get_tmp = (*env).GetMethodID(r_info_jcls, "getTmp", "()I");
jint val_rinfo_tmp = (*env).CallIntMethod(rInfo, jmid_rinfo_get_tmp);
LOGE("ndk ->ndk -> val_rinfo_tmp = %d", val_rinfo_tmp);


// 在c層中構建WeatherInfo物件，設定資料,可以通過呼叫方法也可以通過設定成員變數來實現
jclass w_info_jcls = (*env).FindClass("com/example/hncpp/WeatherInfo");
// 找到構造方法id,無參構造
jmethodID jmid_const_w_info = (*env).GetMethodID(w_info_jcls, "<init>", "()V");
// 構建java物件
jobject jobj_w_info = (*env).NewObject(w_info_jcls, jmid_const_w_info);
// 設定屬性可以通過呼叫GetFieldID->SetFileID來設定，也可以通過GetMethodId->CallMethodId,總之，哪個方便用哪個
// 我們這裡用簡單的操作
jmethodID jmid_winfo_setid = (*env).GetMethodID(w_info_jcls, "set_id", "(I)V");
(*env).CallVoidMethod(jobj_w_info, jmid_winfo_setid, 35);

jmethodID jmid_winfo_setdate = (*env).GetMethodID(w_info_jcls, "setDate",
"(Ljava/lang/String;)V");
(*env).CallVoidMethod(jobj_w_info, jmid_winfo_setdate, r_info_date_jstr);

jmethodID jmid_winfo_settmp = (*env).GetMethodID(w_info_jcls, "setTmp", "(I)V");
(*env).CallVoidMethod(jobj_w_info, jmid_winfo_settmp, val_rinfo_tmp);
return jobj_w_info;
}

2.c呼叫java成員變數\方法\建立java層物件

Utils類程式碼

public class Utils {
public static String TEST_LOG_TAG = "zzg_log";
private static String TEST_LOG_TAG2 = "zzg_log_2";
private static int build_num = 35;
public String app_old_version = "v0.0.3";
public long person_id = 430644198806230032l;
private String app_version = "v1.3.0";
private int test_num = 50;
private long phone_num = 13244105539l;

private Utils() {
Log.e(TEST_LOG_TAG, "私有構造觸發了");
}

public Utils(int t) {
Log.e(TEST_LOG_TAG, "公有構造觸發了,param = " + t);
}

public static void logE(String str) {
Log.e(TEST_LOG_TAG, str);
}

public static void logE(String logTag, String str) {
Log.e(logTag, str);
}

private static long getAppRunTimer() {
return 3500l;
}

private boolean isAppRunning() {
return true;
}

public native void test();
}

java方法

cpp程式碼

公有靜態成員變數呼叫

//公開的靜態方法和成員變數
jclass jcls = env->GetObjectClass(jobj);

//呼叫java的靜態成員變數
jfieldID jfid = (*env).GetStaticFieldID(jcls, "TEST_LOG_TAG", "Ljava/lang/String;");
jstring jlog_tag = static_cast<jstring>((*env).GetStaticObjectField(jcls, jfid));
const char *jlogtag_str = (*env).GetStringUTFChars(jlog_tag, 0);
(*env).ReleaseStringUTFChars(jlog_tag, jlogtag_str);
LOGE("獲取到的屬性 log_tag value = %s", jlogtag_str);

呼叫私有java的靜態成員變數

jfieldID log2_jfid = (*env).GetStaticFieldID(jcls, "TEST_LOG_TAG2", "Ljava/lang/String;");
jstring jlog2_tag = static_cast<jstring>((*env).GetStaticObjectField(jcls, log2_jfid));
const char *jlog2tag_str = (*env).GetStringUTFChars(jlog2_tag, 0);
(*env).ReleaseStringUTFChars(jlog2_tag, jlog2tag_str);
LOGE("獲取到的屬性 log_tag jlog2_tag = %s", jlog2tag_str);

呼叫java的公有靜態方法

jmethodID loge_m = (*env).GetStaticMethodID(jcls, "logE", "(Ljava/lang/String;)V");
jstring log_c = (*env).NewStringUTF("從c呼叫的方法,請重新整理介面");
(*env).CallStaticVoidMethod(jcls, loge_m,log_c);

呼叫java的公有非靜態成員變數

jfieldID jfid = (*env).GetFieldID(jcls, "app_old_version", "Ljava/lang/String;");
jstring jlog_tag = static_cast<jstring>((*env).GetObjectField(jobj, jfid));
const char *jlogtag_str = (*env).GetStringUTFChars(jlog_tag, 0);
(*env).ReleaseStringUTFChars(jlog_tag, jlogtag_str);
LOGE("獲取到的屬性 log_tag value = %s", jlogtag_str);

呼叫私有非靜態的成員變數

//GetFieldID預設獲取的就是私有的
jfieldID jfid = (*env).GetFieldID(jcls, "test_num", "I");
jint test_n = (*env).GetIntField(jobj, jfid);
LOGE("獲取到的屬性 test_num value = %d", test_n);

呼叫私有非靜態的成員String變數

jfieldID app_vers_fid = (*env).GetFieldID(jcls, "app_version", "Ljava/lang/String;");
// 這裡容易傳錯GetObjectField(jobj, app_vers_fid)可千萬要注意
jobject app_vers_obj = (*env).GetObjectField(jobj, app_vers_fid);
jstring app_ver_str = static_cast<jstring>(app_vers_obj);
if (app_ver_str != NULL) {
const char *app_ver_cstr = (*env).GetStringUTFChars(app_ver_str, 0);
(*env).ReleaseStringUTFChars(app_ver_str, app_ver_cstr);
LOGE("獲取到的屬性 log_tag app_version = %s", app_ver_cstr);
}

呼叫公私有非靜態的成員long變數

person_id公有

jfieldID person_id_fid = (*env).GetFieldID(jcls, "person_id", "J");
// 這裡容易傳錯GetObjectField(jobj, app_vers_fid)可千萬要注意
jlong person_id = (*env).GetLongField(jobj, person_id_fid);
LOGE("獲取到的屬性 log_tag person_id = %lld", person_id);

phone_num私有

jfieldID phone_num_fid = (*env).GetFieldID(jcls, "phone_num", "J");
// 這裡容易傳錯GetObjectField(jobj, app_vers_fid)可千萬要注意
jlong phone_num = (*env).GetLongField(jobj, phone_num_fid);
LOGE("獲取到的屬性 log_tag phone_num = %lld", phone_num);

3. static native 使用示例

3. static native 靜態的native方法

c程式碼中呼叫java中的方法示例

java程式碼

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

public static native void updateTag(String key);
}

cpp程式碼

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不會走構造方法
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()));
}

輔助資料

ndk編譯之後so的路徑

\HelloNdkCpp\ZYFramework\build\intermediates\cmake\debug\obj\x86

方法的方法簽名的檢視

as 3.1.2

app/build/intermediates/classes/debug/com/example/hncpp

as 3.3.0

cmd -> javap -s Utils

public class com.example.hncpp.Utils {
public java.lang.String app_old_version;
descriptor: Ljava/lang/String;
public static java.lang.String TEST_LOG_TAG;
descriptor: Ljava/lang/String;
public com.example.hncpp.Utils(int);
descriptor: (I)V

public static void logE(java.lang.String);
descriptor: (Ljava/lang/String;)V

public static void logE(java.lang.String, java.lang.String);
descriptor: (Ljava/lang/String;Ljava/lang/String;)V

public native void test();
descriptor: ()V

static {};
descriptor: ()V
}