Cocos2d-x first school (16)-> C ++ through JNI and Java data mutual

Reprinted! Please indicate the source when reprint: http://write.blog.csdn.net/postedit/8182856

I haven't updated my blog for more than a week. It is estimated that many people are asking me what the bloggers are doing recently! I have not published any new blog posts. Since I went out of my unemployment status last week, and then introduced myself to the group, some friends gave me a job recommendation, I would like to thank him and so many friends for their affirmation... thank you very much!

JNI estimates that most of my friends will be afraid of hearing this ~ If you have never touched on it, it's a big task.

First, let's take a look at some knowledge points:

1. Relationship table for basic data type pairs:

In fact, a closer look shows that the corresponding Java type is pulled by the first letter. boolean is special,
Corresponding to Z, long
Corresponding to J

2. the Java method maps to the signature in C :(Describes the signatures corresponding to the four methods)

Public void test () {} () V

Public void test1 (int I) {} (I) V

Public int Test2 () {return 1;} () I

Public int test3 (int I) {return I;} (I) I

3. Reference Data Type: It is troublesome. It starts with "L" and ends with ";" and corresponds to this type of path in the middle.

For example, string: ljava/lang/string;

Object: ljava/lang/object;

The custom cat class corresponds to package com. duicky;

Cat: lcom/duicky/CAT;

4. array representation:"[" Is used as the flag when the array is represented, and a "[" is used as the one-dimensional array.

For example, int []: [I

Long [] []: [J

Object [] [] []: [[ljava/lang/object;

5,View the JDK SignatureWrite a test class using the following methods:

public void test(){}public void test1(int i){}public int test2(){ return 1;}public int test3(int i) { return i;}public Cat test4(Cat c){ return new Cat();}public Object test5(int [] a){ return null;}public int[][] test5(long [][] b){ return null;}public void test6(Object[][][] b){}

Open cmd command line, CD to generate test class open cmd command line, CD to generate test class directory:

 

CD to the corresponding folder

Enter the command javap-s and the class name of the method signature you want to view.

For example, the javap-s test result shows the desired signature.

 

6. Java calls the C method:

Step 1: Compile the native method:

Private native int fromC ();

Step 2: Compile JNI: (I directly use the main. cpp method in cocos2dx, and then write it to woo ~ in extern "C ~ For ease of viewing, other code is omitted)

using namespace cocos2d;using namespace cocos2d::extension;using namespace std;extern "C"{jint Java_potter_back_MyHelloWorld_fromC(){return 222;}

Step 3: Call the NATIVE METHOD

package potter.back;public class Main {public static void main(String[] args) {System.out.println("fromC++"+new Main().fromC());}private native int fromC();}

7. c calls the Java method: Let's look at it later. Use this method to typeset it later ~

 

Call the JNI Method

package potter.back;public class Main {public static void main(String[] args) {new Main().fromJava();}private native int fromJava();}class Potter {public void fromJava(String msg){System.out.println("From Android");}}

Compile the JNI Method

Void java_potter_back_myhelloworld_fromjava (jnienv * jnienv, jobject thiz) {// ing Class jclass Potter = jnienv-> findclass ("Potter/back/Potter "); // ing construc_id = jnienv-> getmethodid (Potter, "<init>", "() V "); // create the object jobject mpotter = jnienv-> newobject (obj_class, construction_id); // map the object method jmethodid fromjava = jnienv-> getmethodid (Potter, "fromjava ", "(ljava/lang/string;) V"); // call the fromjava method jnienv-> callvoidmethod (mpotter, fromjava, jstrmsg) of the Java object mpotter );}

 8. Passing Java objects through JNI:

Step 1:

Public class main {public static void main (string [] ARGs) {New Main (). javaobjecttoc ();} public void javaobjecttoc () {// call the method in Java through C ++, and then pass the person object person P = new person (24); ccalljava (P ); system. out. println ("P's age =" + P. age);} public native void ccalljava (person P);} class person {public int age; Public Person (INT age) {This. age = age;} public void walk () {system. out. println ("person can walk ");}}

Step 2:

Void java_potter_back_myhelloworld_fromjava (jnienv * jnienv, jobject thiz, jobject OBJ) {// get the person class: Get the handle of the object jclass CLS = jnienv-> getobjectclass (OBJ ); jfieldid FID = jnienv-> getfieldid (CLS, "Age", "I"); jmethodid mid = jnienv-> getmethodid (CLS, "walk", "() V "); int value = jnienv-> getintfield (OBJ, FID); jnienv-> setintfield (OBJ, FID, 6); jnienv-> callvoidmethod (OBJ, mid );}

Step 3: Run

Person can walk

P's age = 6 // This value has been modified ~ The accident was 24, and then JNI was set to 6.

 

9. Java transmits the C ++ object through JNI: (In this method, I have searched for n more materials, but I have not found any corresponding materials. However, using the 7 subtitles, this method can be used for data transmission)
If you know more direct solutions, please let me know... thank you very much ~

Thank you for reading my blog and hope you can see your footprints!
If something is wrong or incorrect,I also hope you can point it out!

References: http://www.cnblogs.com/luxiaofeng54/archive/2011/08/18/2143977.html