android jni介紹

標籤：eof   方法調用   參數類型   main   exce   bundle   array   gets   ppc   

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++通訊橋樑
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native方法傳遞）

native普通方法與靜態方法區別：Jni傳遞參數是jobject和jclass區別

android studio ndk api自動補齊
安裝外掛程式：
Android NDK Support
NDK WorkspaceManager Support

屬性，方法，數組例子：
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");}@Overrideprotected 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());    //測試方法調用    tv.setText(getJavaMethod());    //測試數組操作    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層出現了異常，那麼Java的代碼調用中止    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返回字串public native String updateStringFromC();//調用Java方法public native String getJavaMethod();//對array數組進行排序操作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 JNICALLJava_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數組進行操作extern "C"JNIEXPORT void JNICALLJava_com_home_adproj_androidndktest_MainActivity_operateArraySort(JNIEnv *env, jobject instance,                                                                  jintArray array_) {    jint *arrays = env->GetIntArrayElements(array_, NULL);    int _len = env->GetArrayLength(array_);//擷取數組長度    //qsort(void* __base, size_t __nmemb, size_t __size, int (*__comparator)(const void* __lhs, const void* __rhs));    qsort(arrays,_len, sizeof(int),compare);//數組排序    env->ReleaseIntArrayElements(array_, arrays, 0);//釋放}//調用Java層方法extern "C"JNIEXPORT jstring JNICALLJava_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;");//(參數類型)Ljava/lang/String傳回值類型    jstring result = (jstring) env->CallObjectMethod(instance, _jmethodID,100);    char* str = (char *) env->GetStringUTFChars(result, NULL);//string 轉char    return env->NewStringUTF(str);}//測試Java屬性操作extern "C"JNIEXPORT jstring JNICALLJava_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:屬性名稱  sig:屬性類型    jfieldID _jfieldID = env->GetFieldID(_jclass,"strName","Ljava/lang/String;");    jstring _result = (jstring) env->GetObjectField(instance, _jfieldID);    //如何轉化成java string    char* str = (char *) env->GetStringUTFChars(_result, NULL);    char text[20] = "success";    return env->NewStringUTF(strcat(str,text));}extern "C"JNIEXPORT jstring JNICALLJava_com_home_adproj_androidndktest_MainActivity_stringFromJNI(        JNIEnv* env,        jobject /* this */) {    std::string hello = "Hello from C++";    return env->NewStringUTF(hello.c_str());}

lldb：jni調試工具
官網：http://lldb.llvm.org/tutorial.html

android jni介紹