android jni介绍 _Android

丈夫志四海，万里犹比邻。这篇文章主要讲述android jni介绍相关的知识，希望能为你提供帮助。
【android jni介绍】Jni API:https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/jniTOC.html
JNIEnv、jobject和jclass这三种基本类型
操作API都在JNIEnv中，JNIEnv为java与C/C++通信桥梁
jobject：Java层传递的对象（普通native方法传递）
jclass:Java层对应的Class类（静态native方法传递）
native普通方法与静态方法区别：Jni传递参数是jobject和jclass区别
android studio ndk api自动补齐
安装插件：
Android NDK Support
NDK WorkspaceManager Support
属性，方法，数组例子：
Java层
public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity"; //测试属性 public String strName ="test"; //排序数组 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); //测试属性操作 tv.setText(updateStringFromC()); //测试方法调用 tv.setText(getJavaMethod()); //测试数组操作 this.operateArraySort(array); for (int i = 0; i < array.length; i++){ Log.e(TAG, "onCreate: " + array[i]); }//异常处理 C++的异常 JAVA是无法try catch的，如果jni层出现了异常，那么Java的代码调用中止 try { exception(); }catch (Exception e){ Log.e(TAG, "onCreate: " + e.getMessage()); } Log.e(TAG, "onCreate: " + "end"); } //测试方法 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(); //从C返回字符串 public native String updateStringFromC(); //调用Java方法 public native String getJavaMethod(); //对array数组进行排序操作 public native void operateArraySort(int[] array); //异常处理 public native void exception();

}
Jni层：

#include < jni.h> #include < string> #include "stdlib.h"//C C++混编int compare(const void* lhs, const void* rhs){ return (*(int*)lhs - *(int*)rhs); }//异常处理 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不存在有异常 if(env-> ExceptionCheck()){//检测异常 env-> ExceptionClear(); //清除异常不会使Java层崩溃 //抛异常给Java层 jclass exceptionClass = env-> FindClass("java/lang/IllegalArgumentException"); env-> ThrowNew(exceptionClass,"strName2 不存在"); //抛异常到Java层，Java层进行捕获 } }//对Java数组进行操作 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_); //获取数组长度 //qsort(void* __base, size_t __nmemb, size_t __size, int (*__comparator)(const void* __lhs, const void* __rhs)); qsort(arrays,_len, sizeof(int),compare); //数组排序 env-> ReleaseIntArrayElements(array_, arrays, 0); //释放 }//调用Java层方法 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; "); //(参数类型)Ljava/lang/String返回值类型 jstring result = (jstring) env-> CallObjectMethod(instance, _jmethodID,100); char* str = (char *) env-> GetStringUTFChars(result, NULL); //string 转char return env-> NewStringUTF(str); }//测试Java属性操作 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:属性名sig:属性类型 jfieldID _jfieldID = env-> GetFieldID(_jclass,"strName","Ljava/lang/String; "); jstring _result = (jstring) env-> GetObjectField(instance, _jfieldID); //如何转化成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调试工具
官网：http://lldb.llvm.org/tutorial.html