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I'm trying to call the function through the environment variableenv, namelyenv->FindClass("android/os/BatteryManager"), but eventually the error

F/libc    (27883): Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 27883 (meerkat.rukkola), pid 27883 (meerkat.rukkola)*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***Build fingerprint: 'google/sdk_gphone64_x86_64/emu64xa:15/AE3A.240806.005/12228598:user/release-keys'Revision: '0'ABI: 'x86_64'Timestamp: 2025-08-08 12:01:41.442403800+0000Process uptime: 11sCmdline: com.nelset.meerkat.rukkolapid: 27883, tid: 27883, name: meerkat.rukkola  >>> com.nelset.meerkat.rukkola <<<uid: 10254signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0000000000000000Cause: null pointer dereference    rax 0000000000000000  rbx 00007e848cb2efa0  rcx 00007e830a51c189  rdx 00007e848cb2efa0    r8  0000000000000400  r9  0000000000400010  r10 00007e848d206f90  r11 0000000000000000    r12 00007e848cdbbbdc  r13 00007e8300008081  r14 00007e855d49b3f0  r15 00007e830a711721    rdi 00007ffe279b2c10  rsi 00007e848cb2e905    rbp 00007ffe279b30e0  rsp 00007ffe279b30c8  rip 00000000000000005 total framesbacktrace:      #00 pc 0000000000000000  <unknown>      #01 pc 0000000000000cf0  /data/app/~~a1Xqb36CA6Sv_f1JdZKm8Q==/com.nelset.meerkat.rukkola-l9SGe0rQMJa1u9lgl8wPFQ==/lib/x86_64/libbattery_info_ffi.so (_JNIEnv::FindClass(char const*)+32) (BuildId: d00d0ba3ecc382809f198710bd41789e3cfc5db1)      #02 pc 0000000000000c2f  /data/app/~~a1Xqb36CA6Sv_f1JdZKm8Q==/com.nelset.meerkat.rukkola-l9SGe0rQMJa1u9lgl8wPFQ==/lib/x86_64/libbattery_info_ffi.so (Java_com_example_battery_info_ffi_BatteryInfoFfiPlugin_getBatteryLevel+31) (BuildId: d00d0ba3ecc382809f198710bd41789e3cfc5db1)      #03 pc 0000000000000fc0  /data/app/~~a1Xqb36CA6Sv_f1JdZKm8Q==/com.nelset.meerkat.rukkola-l9SGe0rQMJa1u9lgl8wPFQ==/lib/x86_64/libbattery_info_ffi.so (get_battery_level+32) (BuildId: d00d0ba3ecc382809f198710bd41789e3cfc5db1)      #04 pc 0000000000006fea  [anon:dart-code]Lost connection to device.

comes out when processing the method.Code frombattery_info_android.cpp:

#include <jni.h>extern "C" JNIEXPORT jint JNICALLJava_com_example_battery_info_ffi_BatteryInfoFfiPlugin_getBatteryLevel(JNIEnv *env, jobject thiz){    // Получаем уровень заряда батареи через Android NDK    jclass batteryManagerClass = env->FindClass("android/os/BatteryManager");    jmethodID getSystemService = env->GetStaticMethodID(batteryManagerClass, "getSystemService", "(Ljava/lang/String;)Ljava/lang/Object;");    jstring serviceName = env->NewStringUTF("batterymanager");    jobject batteryManager = env->CallStaticObjectMethod(batteryManagerClass, getSystemService, serviceName);    jmethodID getIntMethod = env->GetMethodID(batteryManagerClass, "getIntProperty", "(I)I");    jint batteryLevel = env->CallIntMethod(batteryManager, getIntMethod, 4); // 4 = BATTERY_PROPERTY_CAPACITY    return batteryLevel;}extern "C" JNIEXPORT jboolean JNICALLJava_com_example_battery_info_ffi_BatteryInfoFfiPlugin_isCharging(JNIEnv *env, jobject thiz){    // Проверяем, заряжается ли устройство    return JNI_FALSE;}// Функции для Dart FFIextern "C" JNIEXPORT jint JNICALLget_battery_level(JNIEnv *env, jobject thiz, jobject context){    return Java_com_example_battery_info_ffi_BatteryInfoFfiPlugin_getBatteryLevel(env, thiz);}extern "C" JNIEXPORT jboolean JNICALLis_charging(JNIEnv *env, jobject thiz, jobject context){    return Java_com_example_battery_info_ffi_BatteryInfoFfiPlugin_isCharging(env, thiz);}

Code fromBatteryInfoFfiPlugin.java:

package com.example.battery_info_ffi;import androidx.annotation.NonNull;import io.flutter.embedding.engine.plugins.FlutterPlugin;import io.flutter.plugin.common.MethodCall;import io.flutter.plugin.common.MethodChannel;import android.content.Context;import android.os.Looper;public class BatteryInfoFfiPlugin implements FlutterPlugin, MethodChannel.MethodCallHandler {    private MethodChannel channel;    private Context context;    static {        System.loadLibrary("battery_info_ffi");    }    @Override    public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {        context = binding.getApplicationContext();        channel = new MethodChannel(binding.getBinaryMessenger(), "battery_info_ffi");        channel.setMethodCallHandler(this);    }    @Override    public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {        channel.setMethodCallHandler(null);    }    @Override    public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {        if (Looper.myLooper() == null) {            Looper.prepare();        }        try{            if (call.method.equals("getBatteryLevel")) {                result.success(getBatteryLevel());            }            if (call.method.equals("isCharging")) {                result.success(isCharging());            } else {                result.notImplemented();            }        }catch(Exception e){            result.error("NATIVE_ERROR", e.getMessage(), null);        }            }    public native int getBatteryLevel();    public native boolean isCharging();}

Full project:battery_info

I tried to do this throughandroid.content.Context, passing it to native methods, but the result was no different, and similar errors were given. I also tried testing on other devices, with a different one, but the result is the same.

Drew Dormann's user avatar
Drew Dormann
65.5k14 gold badges133 silver badges200 bronze badges
askedAug 9 at 13:04
Dmitry's user avatar
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  • 2
    env is not an environment variable. There are nogetSystemService method inandroid/os/BatteryManager class. ¿Perhaps you meant to useandroid.content.Context? Each JNI call requires appropriate error checking that this code lacks.CommentedAug 9 at 13:31
  • I've been working on this problem for a long time, but it has brought me a comprehensive understanding of how native programming works. If you call native methods via_library.lookupFunction, the java file is bypassed and functions from c++ are called directly, while incorrect parameters are passed. I've redone it so that now the methods are called viaMethodChannel, and then the calls are intercepted in the Java file. With this approach, I pass all the parameters correctly, but I will need to learn how to intercept calls in ios and other platforms. All the changes are on gitgub.CommentedAug 9 at 15:12
  • In addition your code misses error handling. E.g.findClass can returnNULL and I assumeGetStaticMethodID will returnNULL, too if the method does not exist.CommentedAug 9 at 16:40
  • "If you call native methods via _library.lookupFunction, the java file is bypassed and functions from c++ are called directly, while incorrect parameters are passed. " That makes no sense and is not how JNI works. Especially since nothing in the Flutter package exists in JNI, it absolutely can't be how it works. MethodChannel may have something to do with communication with Flutter, but it does not with Java calling C or C++CommentedAug 10 at 2:12
  • I would also suggest, if you're calling this via flutter to Java to C, to post the flutter end as wellCommentedAug 10 at 2:22

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