NDK，在JNI层使用AssetManager读取文件

NDK，二进制文件数据读取，在JNI层，通过AAssetManager读取asset内部的资源：

　　需要头文件的支持
　　#include <android/asset_manager_jni.h>
　　#include <android/asset_manager.h>

1，首先传个AssetManager到JNI层；
    AssetManager assetManager = getAssets();
2，将你的数据放到assets文件夹中，然后和对应的文件名字一起，通过JNI Native函数传递到JNI:
    readFromAssets(assetManager, "yourdata.bin");
3，然后在JNI的Native实现函数中读取：(也可直接在对应的C函数调用，调用方法类似fopen，fread)

JNIEXPORT  jstring JNICALL Java_com_lib_MyLib_readFromAssets(JNIEnv* env, jclass clazz,
        jobject assetManager, jstring dataFileName) {
        
    AAssetManager* mManeger = AAssetManager_fromJava(env, assetManager);
    jboolean iscopy;
    const char *dataFile = env->GetStringUTFChars(dataFileName, &iscopy);
    
    int c = dataRead(mManeger, dataFile);  //call the C function

    env->ReleaseStringUTFChars(dataFileName, dataFile);
    
    jstring resultStr;
    resultStr = env->NewStringUTF("success");
    return resultStr;
}
int dataRead(AAssetManager* mManeger, const char *dataFile){

    AAsset* dataAsset = AAssetManager_open(mManeger, dataFile, AASSET_MODE_UNKNOWN);//get file read AAsset
    off_t dataBufferSize = AAsset_getLength(dataAsset);
    
    int num = dataBufferSize/sizeof(float);  
    
    //float *data = (float*) malloc(num * sizeof(float));  //allocate the data, the same with the later line
    float *data = (float*) malloc(dataBufferSize);
    
    int numBytesRead = AAsset_read(dataAsset, data, dataBufferSize);  //begin to read data once time
　　//note: numBytesRead is the total bytes, then num = dataBufferSize/sizeof(float) = numBytesRead/sizeof(float)

    if (numBytesRead<0) {
        LOGI("read data failed");
    }
    else{
        LOGI("numBytesRead: %d", numBytesRead);
    }
    
    //int numBytesRead;
    //for (int i = 0; i < num; i++) {
    //    numBytesRead = AAsset_read(dataAsset, (char*) (&data[i]), sizeof(float));   //or read the data one by one
    //    if (numBytesRead<0) {
    //        LOGI("read data failed");
    //    }
    //    else{
    //        LOGI("numBytesRead: %d", numBytesRead);
    //    }
    //}
    
    AAsset_close(dataAsset);
    free(data);
    
    return 0;
}