android jni介紹

Jni API:https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/jniTOC.html
JNIEnv、jobject和jclass這三種基本類型

操作API都在JNIEnv中，JNIEnv為Java與C/C++通信橋梁
jobject：Java層傳遞的對象（普通native方法傳遞）
jclass:Java層對應的Class類（靜態(tài)native方法傳遞）

native普通方法與靜態(tài)方法區(qū)別：Jni傳遞參數(shù)是jobject和jclass區(qū)別

android studio ndk api自動補齊
安裝插件：
Android NDK Support
NDK WorkspaceManager Support

屬性，方法，數(shù)組例子：
Java層
public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";
//測試屬性
public String strName ="test";

//排序數(shù)組
private int[] array = {89,2,4,34,88,100,1};
// Used to load the 'native-lib' library on application startup.
static {
    System.loadLibrary("native-lib");
}

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

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

    //測試屬性操作
    tv.setText(updateStringFromC());
    //測試方法調(diào)用
    tv.setText(getJavaMethod());

    //測試數(shù)組操作
    this.operateArraySort(array);
    for (int i = 0; i < array.length; i++){
        Log.e(TAG, "onCreate: " + array[i]);
    }

    //異常處理 C++的異常 JAVA是無法try catch的，如果jni層出現(xiàn)了異常，那么Java的代碼調(diào)用中止
    try {
        exception();
    }catch (Exception e){
        Log.e(TAG, "onCreate: " + e.getMessage());
    }
    Log.e(TAG, "onCreate: " + "end");

}
//測試方法
public String getMethod(int a){
    return "method" + a;
}

/**
 * A native method that is implemented by the 'native-lib' native library,
 * which is packaged with this application.
 */
public native String stringFromJNI();
//從C返回字符串
public native String updateStringFromC();
//調(diào)用Java方法
public native String getJavaMethod();
//對array數(shù)組進行排序操作
public native void operateArraySort(int[] array);
//異常處理
public native void exception();

}

Jni層：

#include <jni.h>
#include <string>
#include "stdlib.h"

//C C++混編

int compare(const void* lhs, const void* rhs){
    return (*(int*)lhs - *(int*)rhs);
}

//異常處理
extern "C"
JNIEXPORT void JNICALL
Java_com_home_adproj_androidndktest_MainActivity_exception(JNIEnv *env, jobject instance) {
    jclass  _jclass = env->GetObjectClass(instance);
    jfieldID _jfieldID = env->GetFieldID(_jclass,"strName2","Ljava/lang/String;");//strName2不存在有異常
    if(env->ExceptionCheck()){//檢測異常
        env->ExceptionClear();//清除異常 不會使Java層崩潰
        //拋異常給Java層
        jclass exceptionClass = env->FindClass("java/lang/IllegalArgumentException");
        env->ThrowNew(exceptionClass,"strName2 不存在");//拋異常到Java層，Java層進行捕獲
    }
}

//對Java數(shù)組進行操作
extern "C"
JNIEXPORT void JNICALL
Java_com_home_adproj_androidndktest_MainActivity_operateArraySort(JNIEnv *env, jobject instance,
                                                                  jintArray array_) {
    jint *arrays = env->GetIntArrayElements(array_, NULL);
    int _len = env->GetArrayLength(array_);//獲取數(shù)組長度
    //qsort(void* __base, size_t __nmemb, size_t __size, int (*__comparator)(const void* __lhs, const void* __rhs));
    qsort(arrays,_len, sizeof(int),compare);//數(shù)組排序
    env->ReleaseIntArrayElements(array_, arrays, 0);//釋放
}

//調(diào)用Java層方法
extern "C"
JNIEXPORT jstring JNICALL
Java_com_home_adproj_androidndktest_MainActivity_getJavaMethod(JNIEnv *env, jobject instance) {
    jclass _jclass =env->GetObjectClass(instance);
    //(jclass clazz, const char* name, const char* sig)
    jmethodID _jmethodID = env->GetMethodID(_jclass,"getMethod","(I)Ljava/lang/String;");//(參數(shù)類型)Ljava/lang/String返回值類型
    jstring result = (jstring) env->CallObjectMethod(instance, _jmethodID,100);
    char* str = (char *) env->GetStringUTFChars(result, NULL);//string 轉(zhuǎn)char
    return env->NewStringUTF(str);
}

//測試Java屬性操作
extern "C"
JNIEXPORT jstring JNICALL
Java_com_home_adproj_androidndktest_MainActivity_updateStringFromC(JNIEnv *env, jobject instance) {
    // TODO
    jclass _jclass = env->GetObjectClass(instance);
    //(jclass clazz, const char* name, const char* sig)
    //name:屬性名  sig:屬性類型
    jfieldID _jfieldID = env->GetFieldID(_jclass,"strName","Ljava/lang/String;");
    jstring _result = (jstring) env->GetObjectField(instance, _jfieldID);

    //如何轉(zhuǎn)化成java string
    char* str = (char *) env->GetStringUTFChars(_result, NULL);

    char text[20] = "success";
    return env->NewStringUTF(strcat(str,text));
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_home_adproj_androidndktest_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

lldb：jni調(diào)試工具
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