Android Native Apps Development


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Palestra ministrada por Eduardo Carrara no App Lab Android realizado no auditório da Intel no dia 11 de Outubro de 2013.

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  • Reuso de códigolegadoounão.
  •çãofoifeitaparaunificar a forma de fornecercódigonativopara a JVM, desta forma:Vendors de diferentes JVMs e criadores de ferramentasnãoprecisariammais se preocupar com a implementação de diferentes interfaces;Desenvolvedorespoderiamcriarumaversão de seucódigonativo e elefuncionariajunto com diferentes VMsNo final substituipadrões de interfaceamentocomo o Netscape JRI, Microsoft RNI e o COM.O que é possívelfazer com jni:Criar, inspecionar e atualizarobjetos JavaChamarmétodos JavaPegar e lançarexceçõesCarregar classes e obtersuasinformaçõesEfetuarverificação de tiposdurante a execução
  • Default system STL support: cassertcctypecerrnocfloatclimitscmathcsetjmpcsignalcstddefcstdintcstdiocstdlibcstringctimecwchar new stl_pair.htypeinfo utilityAnything else is _not_ supported, including std::string or std::vector.Static linking is only supported if the application has only one native moduleDon’t forget to load the used library before yours (ieSystem.loadLibrary("stlport_shared"); )LOCAL_CPPFLAGS := -frtti –fexceptions also works, but LOCAL_CPP_FEATURES is a cleaner way to declare it.Source:ndk\docs\CPLUSPLUS-SUPPORT.html
  • Com um projeto Android jácriado é possíveladicionarsuporte àumabibliotecanativautilizando o próprio Eclipse*
  • Credit: TodorMinchevSystem.loadLibrary() will automatically translate MyLib to libMyLib.soThat’s better than using System.load() that takes the path to the .so file.IDZ:To use native c/c++ code in our java source file, we first need to declare JNI call and load the native library.This is a very simple case for declaring and using JNI native calls in Android* App Java sources. Next, there is two solutions: use “javah” tool to generate the JNI header stubs for native code, and add or modify native code to comply with JNI native headers, or load C++ library and map native calls during class load.
  • -> Java spacecom_example_hellojni_ -> com.example.hellojni packageHelloJni_ -> HelloJni classstringFromJNI( -> stringFromJNI methodJNIEnv* env, -> JNI environmentjobjectthiz) -> HelloJNIjobject instanceSource: IDZ
  • Proven method: That’s how native code is integrated in AOSP itself : get all the native methods registration issues during the load of the library instead of during further function callsYou get rid of functions with a lengthy name that will break when refactoring other parts of the codeYou can add/remove native functions easily (you don’t need to write error prone names by hand or re-run javah and copy/paste parts of it)There is no more potential issue with symbol table (really useful when you want to mix C/C++ code)It is also the best spot to cache Java class/objects references
  • Javap => Java Class File Disassembler ( it is in C++ as this method is the most useful for C++ code.You’ll see on a following slide the only difference between C and C++ JNI codes.Java VM’s representation of type signatures: output of javap:C:\Users\xhallade\workspace\HelloJni>javap -s -classpath bin\classes -p com.example.hellojni.HelloJniCompiled from ""public class com.example.hellojni.HelloJni extends{static {}; Signature: ()Vpublic com.example.hellojni.HelloJni(); Signature: ()Vpublic void onCreate(android.os.Bundle); Signature: (Landroid/os/Bundle;)Vpublic native java.lang.StringstringFromJNI(); Signature: ()Ljava/lang/String;public native java.lang.StringunimplementedStringFromJNI(); Signature: ()Ljava/lang/String;}
  • Add this function to your library. It will be the entry point called during load of your library and it is doing the mapping previously defined.It’s also a good place to get the reference to the JavaVM and other objects (like the main activity) to cache them.Source: and marakana android NDK series
  • ABI = Android Binary Interfaceadb shell getprop | grepabi
  • Se vocêchegouatéaquiparabéns! Agora sua app estáredonda e vocêpodedistribuir. Será?E quandoos bugs aparecemcomodebugarseusmódulosnativos?
  • You may be limited to 16 local references within your JNI environment, so don’t forget to call DeleteLocalRef() after use.
  • Don’t count on these automatically frees too much
  • Previous call for creating a String may return a null object, then it’s likely that an exception has occured.Here is the way to get that exception.
  • You CANNOT do everything in C/C++, only a restricted amount of libraries are exposed in C.Calling Java methods from C/C++ is something you may have to do extensively.Java VM’s representation of type signatures:
  • Android Native Apps Development

    1. 1. Desenvolvendo Apps Nativas com NDK Eduardo Carrara de Araujo Software Analyst – Intel Software
    2. 2. Agenda • • • • • • Entendendo o mundo Android* Nativo Conhecendo suas ferramentas Preparando-se para a batalha Mãos à obra! Quebrou! E agora? Q&A 2
    3. 3. Entendendo o mundo Android* Nativo INTEL CONFIDENTIAL
    4. 4. Apps Home Application Framework User Experience Apps As Engrenagens do Robô Contacts Phone Browser Activity Manager Windows* Manager Content Providers View System Package Manager Telephony Manager Resource Manager Location Manager Libraries … Notification Manager Android* Runtime Surface Manager Media Framework SQLite OpenGL* ES FreeType WebKit SGL Middleware … SSL libc Core Libraries Dalvik Virtual Machine … Operating System Linux* Kernel 4 Display Driver Camera Driver Flash Memory Driver Binder (IPC) Driver Keypad Driver WiFi Driver Audio Drivers Power Management
    5. 5. Nativo VS. Dalvik* • O que é uma aplicação Android* nativa? • O que a Intel já faz por você? Android Runtime Dalvik Virtual Machine Core Libraries 5
    6. 6. Por quê utilizar código nativo? Performance Jogos Processamento Gráfico Criptografia Algoritmos de baixo nível Acesso direto à CPU, GPU e outros recursos de HW • Reuso de código • E por que não utilizar? • • • • • • • Performance • Complexidade 6
    7. 7. Conhecendo suas ferramentas 7 INTEL CONFIDENTIAL
    8. 8. Android* Native Development Kit (NDK) • O que é? • Conjunto de ferramentas que permitem a implementação de partes da aplicação Android utilizando código nativo em linguagens como C ou C++. • A interação entre o código nativo e a app Android é feita utilizando Java Native Interface (JNI).
    9. 9. Java Native Interface (JNI) • O que é? • Interface padrão de programação para interoperabilidade entre bibliotecas nativas de uma plataforma e a máquina virtual Java. • Quando usar? • Acessar funcionalidades dependentes de plataforma não providas pela API padrão do Java. • Re-uso de código. • Porções de código que precisam de tuning de performance. 9
    10. 10. Fluxo de Desenvolvimento com NDK C/C++ Code ndkbuild Makefile Java* calls GDB debug JNI APP_ABI := all or APP_ABI := x86 Android* ApplicationsJava Application SDK APIs Java Framework JNI Native Libs Bionic C Library 10 NDK APIs
    11. 11. Conheça os limites: A Bionic C • Biblioteca C otimizada para a plataforma Android. • Mais leve que a GNU C. • Não segue o padrão POSIX. • Suporte limitado à pthreads. • Acesso às propriedades do Android 12
    12. 12. Preparando-se para a batalha 14 INTEL CONFIDENTIAL
    13. 13. Instalando o Android* NDK • Baixe o SDK: ls/sdk/ndk • Baixe o Intel Beacon Mountain: n • Integre com o ADT e o CDT no Eclipse*
    14. 14. Adicionando Suporte Nativo (Eclipse*) 16
    15. 15. Sem o piloto automático Standard Android* Project Structure 1. Create JNI folder for native sources Native Sources - JNI Folder 2. Reuse or create native c/c++ sources 3. Create Makefile NDK-BUILD will automatically create ABI libs folders. 4. Build Native libraries using NDKBUILD script. 17
    16. 16. Mãos à obra! INTEL CONFIDENTIAL
    17. 17. Hello NDK! • Agora que temos um projeto pronto para utilizar código nativo. Qual o próximo passo? • Como integrar o código Java com o C++? 19
    18. 18. Integrando Funções Nativas com Java • Declarar métodos nativos em Java: • public native String getHelloMessage(); • A aplicação Java deve carregar a biblioteca antes de utilizá-la: • System.loadLibrary("HelloNDK"); • Implementar em sua biblioteca nativa os métodos a serem utilizados pela aplicação • Os pontos de entrada da biblioteca podem ser criados de duas formas: com a ferramenta Javah ou as registrando na função JNI_onLoad na biblioteca. 20
    19. 19. Javah • Gera os “header stubs” apropriados para JNI à partir das classes Java já compiladas. • Example: > javah –d jni –classpath bin/classes com.example.hellojni.HelloJni • Gera o arquivo: com_example_hellojni_HelloJni.h • Com a definição: JNIEXPORT jstring JNICALL Java_com_example_hellojni_HelloJni_stringFromJNI(JN IEnv *, jobject); 21
    20. 20. Javah ... { ... tv.setText( stringFromJNI() ); ... } public native String stringFromJNI(); static { System.loadLibrary("hello-jni"); } jstring Java_com_example_hellojni_HelloJni_stringFromJNI(JNIEnv* env, jobject thiz ) { return (*env)->NewStringUTF(env, "Hello from JNI !"); }
    21. 21. JNI_onLoad • Registro das funções JNI no carregamento da biblioteca. • Utilizado nos módulos nativos do AOSP. • Sujeito a menos erros durante refatoração. • Melhor local para lidar com o caching de referências à objetos Java. 23
    22. 22. JNI_onLoad • Declare a função C++ em sua lib: jstring stringFromJNI(JNIEnv* env, jobject thiz) { return env->NewStringUTF("Hello from JNI !"); } • Crie o mapeamento de funções expostas: static JNINativeMethod exposedMethods[] = { {"stringFromJNI","()Ljava/lang/String;",(void*)stringFromJNI},} • Utilize a ferramenta javap para obter a assinatura dos métodos nativos: javap -s -classpath binclasses -p com.example.hellojni.HelloJni -> Signature: ()Ljava/lang/String; 24
    23. 23. JNI_onLoad extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved) { JNIEnv* env; if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) return JNI_ERR; jclass clazz = env>FindClass("com/intel/applab/nativesample/NativeSample"); if(clazz==NULL) return JNI_ERR; env->RegisterNatives(clazz, exposedMethods, sizeof(exposedMethods)/sizeof(JNINativeMethod)); env->DeleteLocalRef(clazz); return JNI_VERSION_1_6; } 25
    24. 24. Estamos prontos? Não! • Utilizar o arquivo para descrever sua app: • • • • Diretório: jni Descrever os módulos necessários Arquiteturas suportadas: ABI Arquivo opcional mas importante para garantir que seus módulos nativos sejam compilados para diversas plataformas. APP_ABI := armeabi armeabi-v7a x86 Ou APP_ABI := all 26
    25. 25. Build it! • Utilizando Eclipse* • Com a integração ADT e NDK no Eclipse* basta compilar a app para gerar as bibliotecas e empacotar seu apk. • Hardcore Mode • Utilizar o script ndk_build para gerar os módulos. • No diretório raíz de sua app execute: • $NDK/ndk_build 27
    26. 26. Quebrou! E agora? INTEL CONFIDENTIAL
    27. 27. LogCat • Mecanismo básico de logs do Android. No NDK pode ser acessado pela API: <android/log.h> • int __android_log_print(int prio, const char *tag, const char *fmt, ...) • Normalmente utilizado com a macro: • #define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "APPTAG", __VA_ARGS__)) • Exemplo • LOGI("accelerometer: x=%f y=%f z=%f", x, y, z); 29
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    33. 33. Backup
    34. 34. Handling JVM and Java objects from native code
    35. 35. Memory handling of Java objects • Memory handling of Java objects is done by the JVM: • You only deal with references to these objects. • Each time you get a reference, you must not forget to delete it after use so the JVM can free it later • local references are automatically freed when the native call returns to Java • Global references are only created by NewGlobalRef()
    36. 36. Creating a Java string C: jstring string = (*env)->NewStringUTF(env, "new Java String"); C++: jstring string = env->NewStringUTF("new Java String"); Main difference with compiling JNI code in C and in C++ is the nature of env as you can see it here. Remember that otherwise, the API is the same.
    37. 37. Getting a C/C++ string from Java string const char *nativeString = (*env)>GetStringUTFChars(javaString, null); … (*env)->ReleaseStringUTFChars(env, javaString, nativeString); //more secure and efficient: int tmpjstrlen = env->GetStringUTFLength(tmpjstr); char* fname = new char[tmpjstrlen + 1]; env->GetStringUTFRegion(tmpjstr, 0, tmpjstrlen, fname); fname[tmpjstrlen] = 0; … delete fname;
    38. 38. Handling Java exceptions // call to java methods may throw Java exceptions jthrowable ex = (*env)->ExceptionOccurred(env); if (ex!=NULL) { (*env)->ExceptionClear(env); // deal with exception } (*env)->DeleteLocalRef(env, ex);
    39. 39. Calling Java methods On an object instance: jclass clazz = (*env)->GetObjectClass(env, obj); jmethodID mid = (*env)->GetMethodID(env, clazz, "methodName", "(…)…"); if (mid != NULL) (*env)->Call<Type>Method(env, obj, mid, parameters…); Static call: jclass clazz = (*env)->FindClass(env, "java/lang/String"); jmethodID mid = (*env)->GetStaticMethodID(env, clazz, "methodName", "(…)…"); if (mid != NULL) (*env)->CallStatic<Type>Method(env, clazz, mid, parameters…); • (…)…: method signature • parameters: list of parameters expected by the Java method • <Type>: Java method return type
    40. 40. Throwing Java exceptions jclass clazz = (*env->FindClass(env, "java/lang/Exception"); if (clazz!=NULL) (*env)->ThrowNew(env, clazz, "Message"); The exception will be thrown only when the JNI call returns to Java, it will not break the current native code execution.
    41. 41. Usando GDB 45 INTEL CONFIDENTIAL
    42. 42. Debugging with GDB and Eclipse • Native support must be added to your project • Pass NDK_DEBUG=1 to the ndk-build command, from the project properties: NDK_DEBUG flag is supposed to be automatically set for a debug build, but this is not currently the case.
    43. 43. Debugging with GDB and Eclipse* • When NDK_DEBUG=1 is specified, a “gdbserver” file is added to your libraries
    44. 44. Debugging with GDB and Eclipse* • Debug your project as a native Android* application:
    45. 45. Debugging with GDB and Eclipse • From Eclipse “Debug” perspective, you can manipulate breakpoints and debug your project • Your application will run before the debugger is attached, hence breakpoints you set near application launch will be ignored