Android ndk c code calls java code

Here, I will briefly talk about the method for c calling java in ndk. As for the establishment of the ndk environment, I will not talk about it here. If I have time, I will post it for java to call c. I will post it later, let's talk about c to call back the java code. I won't talk about creating a project first. Let's start with a typical example helloworld. Hahaha, step 1. Create a class in the android project and put a method in it, syso is a helloworld. At the same time, we recommend that you create an activity so that you can put a button and click it to see the effect. Here we will expand a little bit. 1: Write a java method public void helloFromJava () {System. out. println ("helloFromJava");} 2: Write the corresponding native METHOD static {System. loadLibrary ("Hello");} public native void callback1 (); 3: implement the call and put it in the button for calling. 4: here we need to use javah to generate the C header file. Of course we can not do this. In addition, I will not expand the second part to create a C file in ndk. # include <jni. h> # include "com_itheima15_ndk4_DataProvider.h" // This header file is generated by javah in jdk. I believe you don't need to introduce how to use javah. // The Log Module, habitually put a log Module for debugging # include <android/log. h> # define LOG_TAG "System. out "# define LOGD (...) _ android_log_print (ANDROID_LOG_DEBUG, LOG_TAG, _ VA_ARGS _) # define LOGI (...) _ android_log_print (ANDROID_LOG_INFO, LOG_TAG, _ VA_ARGS _) JNIEXPORT void JNICALL encode (JNIEnv * env, jobject obj) {// C call the java empty method/** 1. Find the class in which the method exists (find the class that has the method) * 2. Find this method in this class * 3. Execute this method */char * classname = "com/xuchulong/ndk4/DataProvider "; // This is my class name. Put my helloworld in it according to your own situation. // The first step is to find this class // jclass (* FindClass) (JNIEnv *, const char *); jclass clazz = (* env)-> FindClass (env, classname); // find this method in step 1 of this class // jmethodID (* GetMethodID) (JNIEnv *, jclass, const char *, const char *); // jclass find the method name in the class // const char * Find/const char * method signature jdk javap-s get method signature usage: javap-s package name. class Name jmethodID method = (* env)-> GetMethodID (env, clazz, "helloFromJava", "() V"); // execute this method // void (* CallVoidMethod) (JNIEnv *, jobject, jmethodID ,...); (* env)-> CallVoidMethod (env, obj, method);} C code has completed ndk-build.