android jni介绍

2025-01-20 技术教程

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");}@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); //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 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 JNICALLJava_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 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;");//(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 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: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 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调试工具
官网：http://lldb.llvm.org/tutorial.html