Retrieve android.os.Build.... system properties via purely native Android app

Question

I have a purely native Android NDK app, and need to retrieve values such as: android.os.Build.MODEL

Unfortunately I cannot find good examples of how to go about this?

Answer 1

These values are easy to obtain in native code via the interface defined in <sys/system_properties.h>, which has been around since the first NDK release. You just need to know the string identifier used on the Java side. Fortunately, with an open-source OS, we can find these easily. Here is a working example of retrieving the model name.

#include <sys/system_properties.h>

//
// Public codes are defined in http://developer.android.com/reference/java/lang/System.html#getProperty(java.lang.String).
// Codes below are defined in https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/java/android/os/Build.java.
// Items with * are intended for display to the end user.
//

#define ANDROID_OS_BUILD_VERSION_RELEASE     "ro.build.version.release"          // * The user-visible version string. E.g., "1.0" or "3.4b5".
#define ANDROID_OS_BUILD_VERSION_INCREMENTAL "ro.build.version.incremental"      // The internal value used by the underlying source control to represent this build.
#define ANDROID_OS_BUILD_VERSION_CODENAME    "ro.build.version.codename"         // The current development codename, or the string "REL" if this is a release build.
#define ANDROID_OS_BUILD_VERSION_SDK         "ro.build.version.sdk"              // The user-visible SDK version of the framework.

#define ANDROID_OS_BUILD_MODEL               "ro.product.model"                  // * The end-user-visible name for the end product..
#define ANDROID_OS_BUILD_MANUFACTURER        "ro.product.manufacturer"           // The manufacturer of the product/hardware.
#define ANDROID_OS_BUILD_BOARD               "ro.product.board"                  // The name of the underlying board, like "goldfish".
#define ANDROID_OS_BUILD_BRAND               "ro.product.brand"                  // The brand (e.g., carrier) the software is customized for, if any.
#define ANDROID_OS_BUILD_DEVICE              "ro.product.device"                 // The name of the industrial design.
#define ANDROID_OS_BUILD_PRODUCT             "ro.product.name"                   // The name of the overall product.
#define ANDROID_OS_BUILD_HARDWARE            "ro.hardware"                       // The name of the hardware (from the kernel command line or /proc).
#define ANDROID_OS_BUILD_CPU_ABI             "ro.product.cpu.abi"                // The name of the instruction set (CPU type + ABI convention) of native code.
#define ANDROID_OS_BUILD_CPU_ABI2            "ro.product.cpu.abi2"               // The name of the second instruction set (CPU type + ABI convention) of native code.

#define ANDROID_OS_BUILD_DISPLAY             "ro.build.display.id"               // * A build ID string meant for displaying to the user.
#define ANDROID_OS_BUILD_HOST                "ro.build.host"
#define ANDROID_OS_BUILD_USER                "ro.build.user"
#define ANDROID_OS_BUILD_ID                  "ro.build.id"                       // Either a changelist number, or a label like "M4-rc20".
#define ANDROID_OS_BUILD_TYPE                "ro.build.type"                     // The type of build, like "user" or "eng".
#define ANDROID_OS_BUILD_TAGS                "ro.build.tags"                     // Comma-separated tags describing the build, like "unsigned,debug".

#define ANDROID_OS_BUILD_FINGERPRINT         "ro.build.fingerprint"              // A string that uniquely identifies this build. 'BRAND/PRODUCT/DEVICE:RELEASE/ID/VERSION.INCREMENTAL:TYPE/TAGS'.


char model_id[PROP_VALUE_MAX]; // PROP_VALUE_MAX from <sys/system_properties.h>.
int len;
len = __system_property_get(ANDROID_OS_BUILD_MODEL, model_id); // On return, len will equal (int)strlen(model_id).

Answer 2

The NDK isn't meant to replace the Java based API but to supplement it. To get Build you'll have to find its private implementation in C/C++ or provide the information from Java via JNI.

Pseudo Code:

android_main(struct *android_app){
    JNIEnv *env = android_app->activity->env;
    jclass build_class = FindClass(env, "android.os.Build");
    jfieldID brand_id = GetStaticFieldID(env, build_class, "BRAND", "Ljava/lang/String;");
    jstring brand_obj = (jstring)GetStaticObjectField(env, brand_id);
}