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?
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3 Answers
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).
1 Comment
Christian.D
Thanks. That's exactly the information which was missing and which is not obvious or visible anywhere in the public android ndk documentation. Here is a link to the sources if you're interested in the method signatures and contracts: android.googlesource.com/platform/bionic/+/android-1.6_r1/libc/…
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);
}
9 Comments
lost_bits1110
thank-you. I am unable to find its C/C++ implementation, however I can try and retrieve this info from Java via JNI. I see examples for this where 'JNIEnv*` is a function paramater, later used to call methods such as
GetMethodID and CallVoidMethod, however I'm not sure where or how in my native method I could call this from? Where would I get this JNIEnv* parameter from?lost_bits1110
(ie my purely native app has 'android_main` as my entry point into my purely native app, hence i'm not sure how to call a function that takes JNIEnv* as a parameter)
Dan S
Ahh, this is going to be a problem, what kind of information are you looking for from Build?
lost_bits1110
Basically I need the device information, such as Build.MODEL, Build.BRAND, Build.DEVICE and Build.VERSION.RELEASE
Dan S
Are you using "android_native_app_glue.h" or just "native_activity.h" to make your app? From there I can give you some pseudo code.
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I don't think you can do this unfortunately. You could always start in VM and jump down via JNI to native after retrieving the values you want to access.
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