Android JNI Programming 3 (Operations on basic type one-dimensional integer arrays) Summary version

Main learning materials: Black Horse Programmer's Ndk method use (Production class library so)

JNI Programming Guide Chinese (uploaded to blog park)

Blogger article (it uses VS and Eclipse co-development): http://www.cnblogs.com/activity-life/p/3643047.html

//0.incoming one-dimensional integer array with no return value (but modified for array) PublicNativevoidArrayencode (int[] arr);//1.Pass in a one-dimensional array, array length (because C is not easy to get and Java is convenient), return integerPrivateNativeintSumarray (int[] AR,intlength);//Pass the length of an array//2.incoming one-dimensional integer array, infinite set length, return integerPrivateNativeintSumarraya (int[] ar);//No transmission length

Declaring a good local method in Mainactivity.java (implemented by C language)

src folder under javah Instruction compilation generated. h (convenient use of function name)

Configure NDK, (Generate class library, Jni,libs folder)

Modify suffix name:. cpp->.c android.mk source file type modified to. c

C Code:

//0. No return value, enter an array, no lengthJniexportvoidjnicall Java_com_swust_array_mainactivity_arrayencode (jnienv*env, Jobject obj, Jintarray jintarr) {    //get the length of the integer array and the address of the No. 0 element//jsize (*getarraylength) (jnienv*, jarray);        intLength = (*env)getarraylength (env, Jintarr); //jint* (*getintarrayelements) (jnienv*, Jintarray, jboolean*);        int* ARRP = (*env)->getintarrayelements (env, Jintarr, 0); inti;  for(i = 0;i < length; i++){            * (ARRP + i) + = 10; }}//1. There is a return value int type, enter an array, have lengthjniexport jint jnicall java_com_swust_array_mainactivity_sumarray (jnienv*env, Jobject obj, Jintarray arr, jint length) {     intI, sum = 0; Jint* Poutbuf =NULL; if(Length > 0) Poutbuf= (jint*) malloc (length *sizeof (jint)); Else            return0; (*ENV)->getintarrayregion (env, arr, 0, length, poutbuf);  for(i = 0; i < length; i++) Sum+=Poutbuf[i];        Free (POUTBUF); Poutbuf=NULL; returnsum;}//2. There is a return value int type, enter an array, no lengthjniexport jint jnicall Java_com_swust_array_mainactivity_sumarraya (jnienv*env, Jobject obj, Jintarray arr) {    inti,j, sum = 0; Jint*buf; J= (*env)getarraylength (Env,arr); //In addition, the value returned here is jint*, not a const jint*, which means that the values therein can be modifiedBUF = (*env)->getintarrayelements (env, arr, NULL);//This sentence also tells the Java memory collector, do not reclaim the memory of ARR array, or do not defragment the memory//If the collector, recycle and defragment the memory, then we in C, access to the address may be wrong          for(i = 0; i < J; i++)//here is the find -and-fitSum + =Buf[i]; //Now let's change the elements in the BUF and see if we can update the values in the BUF to arr in Java after we return .BUF[0] = 100; buf[1] = 200; (*ENV)->releaseintarrayelements (env, arr, buf, 0);//call this method, tell the Java memory collector that I have run out of arr, and can now reclaim Arr's memory         returnsum;}

Import include (easy to find definition, no warning error)

Calling the local method in Java code

int[] arr = {1,2,3,4,5};  Public voidClick1 (View v) {//Type 1: return value is void type, input one-dimensional array no lengthArrayencode (arr);  for(intI:arr)        {System.out.println (i); }        //Type 2: return value is int, input one-dimensional array has lengthInteger val = Sumarray (arr,5); LOG.D ("WSQ", "after passing array length, and as =" +val); //Type 3: return value int, input one-dimensional array no length//passed in a one-dimensional array, accumulated sum, and modified the value of the No. 0 and 1th array elementsInteger value =Sumarraya (arr); Toast.maketext ( This, value.tostring (), 0). Show (); LOG.D ("WSQ", "arr[0" = "+ arr[0]+" arr[1] "+arr[1]); }    

Effect:

Call Type 1:

Type 2:

Type 3:

Did not learn thoroughly, to apply the main, everybody many advice, 2015-10-25 15:39 notes

Android JNI Programming 3 (Operations on basic type one-dimensional integer arrays) Summary version