android dev

android.md

Basic

• Tutorials about development for Android.

Tips

• HashMap<int,xxx>，HashMap<long,xxx> are both invalid, because HashMap only accept key type that implements Comparable interface What's the Fuck!!! we must use HashMap<Interger,xxx> and HashMap<Long,xxx>. Java also provide another generic collection to solve this problem: LongSparseArray.

NDK

• meta(important!!)

  • keep ndk version is the same as android os version, which will avoid lots exceptions
  • any assert code will lead to segment fault error when call java System.loadlibary() and excute jni functions

• tools

  • os-windows: cygwin
  • androik-ndk
  • android-ndk-googlegroup
  • ndk-build

  'ndk-build' itself is a tiny wrapper around GNU Make, its purpose is simply to invoke the right NDK build script, it is equivalent to; $GNUMAKE -f $NDK/build/core/build-local.mk [parameters] Where '$GNUMAKE' points to GNU Make 3.81 or later, and $NDK points to your NDK installation directory.

  • adb/push/pull location at sdk\platform-tools
    • push multifiles to android in windows:for %i in (*.so) do adb push %i /system/lib/

• jni

  • jni-tutorial
  • jni-tips
  • introduce-to-android-jni-1
  • introduce-to-android-jni-2
  • jni-functions
  • Java Native Interface Programming
  • Debugging Android native shared libraries
  • build
    1. create a new android project in eclipse
    2. add jni directory
    3. add Application.mk
    • add APP_PROJECT_PATH := $(call my-dir) line
    4. add Android.mk
    • addLOCAL_PATH := $(call my-dir)
    • addJNI_PATH := $(APP_PROJECT_PATH)/jni because sometimes ndk has bug that LOCAL_PATH is incorrect, we use custome JNI_PATH

Build Android JNI with Eclipse in windows, Step by Step.

• Download

  • adt-bundle-windows which include
    • eclispe
    • sdk
    • SDK Mangaer.exe
  • android-ndk-rxy(where xy is version number)
  • Java SDK
  • after this step, the tools directory is:

  d:\android
    elipse
    sdk
    ndk
      ndk-build.cmd
    SDK Manager.exe
  

• Create Project, name as hellojni

  • Create New Android Project in Eclispe
  • Create package to declare native methods like

  package com.xxx.yyy
  class ZZZ{
    static{
      System.loadLibrary("hello")
    }
    public native int echo(String msg);
  }
  
  

  • Create jni subdirectory in the project:

  hellojni
    jni
      inc 
      lib
      src    
  

  then, add c/c++ header file in inc directory, add native so files in lib directory

  • Use the following command to generate jni header files:

  javah -d jni/src -classpath src com.xxx.yyy.ZZZ which will gen

  hellojni
    jni
      inc 
      lib
      src    
        com_xxx_yyy_ZZZ.h
  

  • Create com_xx_yyy_ZZZ.cpp file in jni/src, implement the jni functions
  • Create an Application.mk file in hellojni directory, and add text:

  APP_ABI := armeabi
  APP_PLATFORM := android-7
  APP_PROJECT_PATH := $(call my-dir)
  

  • Create an Android.mk file in hellojni/jni/ directory, and add text:

  JNI_PATH := ${local} #this variable is define in elipse builder Environment tab
  
  # include native so
  include $(CLEAR_VARS)
  LOCAL_MODULE := somenative
  LOCAL_SRC_FILES := $(JNI_PATH)/lib/somenative.so
  include $(PREBUILT_SHARED_LIBRARY)
  
  include $(CLEAR_VARS)
  LOCAL_MODULE := hello
  LOCAL_C_INCLUDES := $(JNI_PATH)/inc 
  LOCAL_SRC_FILES := $(JNI_PATH)/src/com_xxx_yyy_ZZZ.cpp
  
  LOCAL_SHARED_LIBRARIES += somenative
  LOCAL_LDLIBS += -lz -llog
  LOCAL_CFLAGS += -O2 -MD -DLINUX -D_ANDROID_LINUX -DMOBILE_PHONE -DDOWNLOAD_PLATFORM_PROJ_BT_EMULE
  include $(BUILD_SHARED_LIBRARY)
  
  

  • Create Eclispe NDK_Builder

    • Open Project Properties dialog in eclipse
    • Goto Builder menu
    • Create a new Builder, Name as 'NDK_Bulder'
    • Edit NDK_Builder
    • Select [Main] Tab
      • Set Location as 'd:\android\ndk\ndk-build.cmd'
      • Set Working Directory as '${workspace_loc:/hellojni}'
    • Select [Refresh] Tab
      • Check "Refresh resource upon completion"
      • Check "The entire workspace"
      • Check "Recuresively include sub-foulders"
    • Select [Build options] Tab
      • Check "After a 'Clean'"
      • Check "During manual builds"
      • Check "During auto builds"
      • Check "Specify working set of relevant resources"
    • Select [Environment] Tab
      • Add a new variable, Name:local Value:${workspace_loc:/hellojni/jni}

  • Back to Eclipse, Build Project.

JNI Signatures

• Type System

Java Type	JNI Type	JNI ArrayType	C Type	C99 Type	JNI Signatures	JNI Array Signatures
boolean	jboolean	jbooleanArray	unsigned char	uint8_t	Z	[I
byte	jbyte	jbyteArray	signed char	int8_t	B	[B
char	jchar	jcharArray	unsigned short	uint16_t	C	[C
short	jshort	jshortArray	short	int16_t	S	[S
int	jint	jintArray	int	int32_t	I	[I
long	jlong	jlongArray	long	int64_t	J	[J
float	jfloat	jfloatArray	float	float	F	[F
double	jdouble	jdoubleArray	double	double	D	[D
void	void	x	void	void	V

• Example
  1. boolean isLenOn(void) -> ()Z
  2. void setLedOn(int lenNo) -> (I)
  3. String substr(String str,int idx,int count) -> (Ljava/lang/String;II)Ljava/lang/String

Reference Types

• jobject (all java objects)
  • jclass (java.lang.Class objects)
  • jstring (java.lang.String objects)
  • jarray (arrays)
    • jobjectArray (object arrays)
    • jbooleanArray (boolean arrays)
    • jbyteArray (byte arrays)
    • jcharArray (char arrays)
    • jshortArray (short arrays)
    • jintArray (int arrays)
    • jlongArray (long arrays)
    • jfloatArray (float arrays)
    • jdoubleArray (double arrays)
  • jthrowable (java.lang.Throwable objects)

Native Built in Type

• jobject/jclass

  • in c program language:

  typedef jobject jclass;
  

  • in c++ program language

  class _jobject{};
  class _jclass : public _jobject{};
  ...
  typedef _jobject* jobject;
  typedef _jclass* jclass;
  

• field/method ids

struct _jfieldID;
typedef struct _jfieldID* jfieldID;
struct _jmethodID;
typedef struct _jmethodID* jmethodID;

• Value Type

typedef union jvalue {
  jboolean z;
  jbyte b;
  jchar c;
  jshort s;
  jint i;
  jlong j;
  jfloat f;
  jdouble d;
  jobject l;
}

• jni 注册实例
  • com.android.server.connectivity.Vpn

Use gdb and gdbserver to debug your native program in android

1. connect your android to your computer
   • assum that the android ip is: 192.168.91.100
   • assum that the computer ip is: 192.168.91.101
2. push gdbserver into android adb push $ANDROID_NDK_ROOT/prebuilt/android-arm/gdbserver/gdbserver /data
3. push all native program into android
   adb push ./app/bin/debug/xxx /data/tmp where ./app/bin/debug/xxx is your program file where /data/tmp is directory in android
4. pull android lib to local, which will be used in gdbserver adb pull /system/lib ./debugging/lib adb pull /system/bin/linker ./debugging/lib
5. run app in android adb shell gdbserver :12345 /data/tmp/app
6. run ndk's gdb in your computer by the following command

   $ANDROID_NDK/toolchains/arm-linux-androideabi-4.4.3/prebuild/darwin-x86/bin/arm-linux-androideabi- gdb
   

   then you will enter the gdb interact enviroment, go to next step
7. tell gdb where to find your so lib (gdb) set solid-serarh-path ./debugging/lib
8. tell gdb the native program you'd like to debug (gdb) file ./app/bin/debug/xxx then gdb will load the symbols from so files
9. connect to gdbserver which is running on the android (gdb) target remote 192.168.91.100:12345
10. begin to debug your program with gdb, for example (gdb) b main (gdb) c where command b is used to set break point where command c is tell gdb to continue
11. that's all, maybe you should learn more gdb command from manual, and gdbserver is just a spy in android to communication with gdb in your computer.