NDK动态库的调用分两种情况。第一种是：so库和调用程序在同一个目录和源程序 通过同一个mk文件来编译；另外一种情况是so是外部已经编译好了的，调用程序加载调用。下面我们就来分析下面2种so的调用情况：
第一部分： 内部so调用
A. 先看下工程的目录：
test01.java :Java文件
test01.c 主so，生成libtest.so，在libtest.so中调用libtutorial.so中的方法
tutorial01.c tutorial02.c tutorial02.h ：生成libtutorial.so
B. 然后看下具体的mk文件的写法以及java中的文件内容
test01.java/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.test;
import android.R.integer;
import android.app.Activity;
import android.widget.TextView;
import android.os.Bundle;
public class test01 extends Activity
{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
/* Create a TextView and set its content.
* the text is retrieved by calling a native
* function.
*/
TextView tv = new TextView(this);
int a = getinformation();
String lls = a +"";
tv.setText(lls);
setContentView(tv);
}
/* A native method that is implemented by the
* 'hello-jni' native library, which is packaged
* with this application.
*/
public native int getinformation();
/* this is used to load the 'hello-jni' library on application
* startup. The library has already been unpacked into
* /data/data/com.example.HelloJni/lib/libhello-jni.so at
* installation time by the package manager.
*/
static {
System.loadLibrary("test");
}
}
Android.mk LOCAL_PATH := $(call my-dir)
#获取当前目录
include $(CLEAR_VARS)
#清除一些变量
LOCAL_MODULE := tutorial
#要生成的库名
LOCAL_SRC_FILES := tutorial01.c tutorial02.c
#库对应的源文件
include $(BUILD_SHARED_LIBRARY)
#生成动态库libtutorial.so
include $(CLEAR_VARS)
#清除一些变量
LOCAL_MODULE := test
#定义另外一个库的名
LOCAL_SRC_FILES := test01.c
#定义库对应的源文件
LOCAL_LDLIBS := -ldl -llog
#libtest.so需要引用的库libdl.so:加载动态函数需要，liblog.so 日志打印需要，默认是system/lib目录下
include $(BUILD_SHARED_LIBRARY)
#生成共享库
test01.c
#include <string.h>
#include <jni.h>
#include <dlfcn.h>
#include <android/log.h>
#include <stdlib.h>
#define LOG_TAG "libgl2jni"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
//extern int getinformation();
jint Java_com_example_test_test01_getinformation(JNIEnv* env,jobject thiz)
{
//getinformation(); ??thr .so file will load to the sdcard with the folder data/data/com.example.test/lib/
void* filehandle = dlopen("/data/data/com.example.test/lib/libtutorial.so", RTLD_LAZY );
int ll = -1;
if(filehandle)
{
LOGI("open so success!");
int( * getinformation ) ();
getinformation = dlsym(filehandle, "getinformation");
if( getinformation )
{
LOGI("call function getinformation OK!");
ll = getinformation();
}
else
{
ll = -3;
LOGE("call function getinformation! ERROR!");
}
LOGI("return value=%d",ll);
dlclose(filehandle);
filehandle=0;
}
else
{
ll = -2;
LOGE("open so ERROR!");
}
return ll;
}
tutorial01.c
#include <stdio.h>
#include "tutorial02.h"
int getinformation()
{
int c = getinformation2(191,81);
return c;
}
tutorial02.c
#include <stdio.h>
#include "tutorial02.h"
int getinformation2(int i,int j)
{
return (i+j);
}
tutorial02.h
int getinformation2(int,int);
C: 编译：
进入工程目录，执行 $NDK/ndk-build
输出结果：
$NDK/ndk-build
/cygdrive/e/cygwin/android-ndk-r4
Compile thumb : test <= /cygdrive/e/cygwin/android-ndk-r4/samples/testappso/jni/test01.c
SharedLibrary : libtest.so
Install : libtest.so => /cygdrive/e/cygwin/android-ndk-r4/samples/testappso/libs/armeabi
Compile thumb : tutorial <= /cygdrive/e/cygwin/android-ndk-r4/samples/testappso/jni/tutorial01.c
Compile thumb : tutorial <= /cygdrive/e/cygwin/android-ndk-r4/samples/testappso/jni/tutorial02.c
SharedLibrary : libtutorial.so
Install : libtutorial.so => /cygdrive/e/cygwin/android-ndk-r4/samples/testappso/libs/armeabi
D：在重新刷新工程，你就可以在lib下面看到生成的so了，点击加载运行
第二部分：调用通过自己编写make方式生成的so
我们还是引用上面的工程，不过把libtutorial.so 拿出来，通过自己写makefile来编译成so，这里请大家注意了，调用外部的so时候，不能够直接用在linux下生产的so来调用，必须通过ndk提供的gcc来编译，否则会因为平台的不同无法调用。
A. 废话不多说，看makefile怎么写！我的ndk是1.6版本的.
新建一个文件夹，把 tutorial01.c tutorial02.c tutorial02.h 文件拷贝过去，然后编写makefile文件
libtutorial.so Makefile
CC = /cygdrive/e/cygwin/android-ndk-r4/build/prebuilt/windows/arm-eabi-4.4.0/bin/arm-eabi-gcc-4.4.0
CFLAGS = -g -O2 -fPIC -I/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/include
SDFLAGS = -nostdlib -Wl,-T,armelf.xsc -Wl,-shared,-Bsymbolic -Wl,-soname,$@ -lc
CRT_OBJS= -L/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/lib -lz -lm -ldl
# source files:
SRCS= tutorial01.c tutorial02.c tutorial02.h
all: libtutorial.so
libtutorial.so: tutorial01.o tutorial02.o
$(CC) $(SDFLAGS) -o $@ tutorial01.o tutorial02.o $(CRT_OBJS)
tutorial01.o: tutorial02.h
tutorial02.o: tutorial02.h
clean:
rm -f libtutorial.so *.o
在执行make的时候需要注意一下几点：
1. 指定程序需要的头文件目录 通过-I指定/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/include NDK提供的一些基本c语言库的头文件
2. 指定库路径-L/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/lib 里面有libz.so,libm.so,libdl.so等库的路径
3. 拷贝交叉编译文件armelf.xsc到android-ndk-r4/build/prebuilt/windows/arm-eabi-4.4.0/lib/gcc/arm-eabi/4.4.0下，armelf.xsc在目录./build/prebuilt/linux-x86/arm-eabi-4.4.0/arm-eabi/lib/ldscripts下
4. 拷贝libc.so到./build/prebuilt/linux-x86/arm-eabi-4.4.0/lib/gcc/arm-eabi/4.4.0目录下，libc.so位于./build/platforms/android-5/arch-arm/usr/lib库
完成上面的工作你就可以放心make了，成功后生成libtutorial.so文件
libtest.so Makefile
CC = /cygdrive/e/cygwin/android-ndk-r4/build/prebuilt/windows/arm-eabi-4.4.0/bin/arm-eabi-gcc-4.4.0
CFLAGS = -g -O2 -fPIC -I/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/include
SDFLAGS = -nostdlib -Wl,-T,armelf.xsc -Wl,-shared,-Bsymbolic -Wl,-soname,$@ -lc
CRT_OBJS= -L/cygdrive/e/cygwin/android-ndk-r4/build/platforms/android-5/arch-arm/usr/lib -lz -lm -ldl
# source files:
SRCS= test01.c
all: libtest.so
libtest.so: test01.o
$(CC) $(SDFLAGS) -o $@ test01.o $(CRT_OBJS)
test01.o: test01.c
clean:
rm -f libtest.so *.o
B. 生成so文件后，在工程目录下建立目录libs/armeabi,然后把so拷贝进去，在打开工程，刷新加载，一切搞定
C. 一些小技巧：
a. 查看so是不是编译成ARM模式下的so
$ file libtest.so
libtest.so: ELF 32-bit LSB shared object, ARM, version 1 (SYSV), dynamically linked, not stripped
b. 如果别人提供了你一个so，查看提供了那些方法，更详细的用法，查看nm命令
$ nm libtutorial.so |grep T
00001344 a _GLOBAL_OFFSET_TABLE_
000002a8 T getinformation
000002b4 T getinformation2
D. 下面提供一个大工程的编译的makefile，吧opencore --omx下的testapp独立编译成so，编译通过，未加载库，给大家参考。
testapp Makefile
cc=/home/zhangweia/android/android-ndk-r4b/build/prebuilt/linux-x86/arm-eabi-4.4.0/bin/arm-eabi-gcc-4.4.0
CFLAGS = -g -O2 -fPIC -DANDROID -I./include -I/home/zhangweia/android/android-ndk-r4b/build/platforms/android-5/arch-arm/usr/include
CFLAGS += -I$(SDK)/out/target/product/generic/obj/include/libpv \
-I$(opencore)/codecs_v2/common/include \
-I$(opencore)/pvmi/pvmf/include \
-I$(opencore)/nodes/common/include \
-I$(opencore)/extern_libs_v2/khronos/openmax/include \
-I$(opencore)/build_config/opencore_dynamic \
-I$(opencore)/android/drm/oma1/src \
-I$(opencore)/engines/author/include \
-I$(opencore)/oscl/oscl/config/shared \
-I$(opencore)/oscl/oscl/config/android \
-I$(opencore)/engines/common/include \
-I$(opencore)/extern_libs_v2/khronos/openmax/include \
-I$(opencore)/android \
#SDFLAGS = -nostdlib -Wl,-T,armelf.xsc -Wl,-shared,-Bsymbolic -Wl,-soname,$@ -lc
SDFLAGS = -nostdlib -Wl,-T,armelf.xsc -Wl,-Bsymbolic -Wl,-soname,$@ -lc
CRT_OBJS=-L/home/zhangweia/android/android-ndk-r4b/build/platforms/android-5/arch-arm/usr/lib -lz -lm -ldl
#all : libomxde.so
OBJECT= omx_threadsafe_callbacks.o \
omxdectest.o \
omxdectestbase.o \
omxtest_buffer_busy.o \
omxtest_corrupt_nal.o \
omxtest_dynamic_reconfig.o \
omxtest_eos_missing.o \
omxtest_extra_partialframes.o \
omxtest_flush_eos.o \
omxtest_flush_port.o \
omxtest_get_role.o \
omxtest_incomplete_nal.o \
omxtest_missing_nal.o \
omxtest_multiple_instance.o \
omxtest_param_negotiation.o \
omxtest_partialframes.o \
omxtest_pause_resume.o \
omxtest_portreconfig_transit_1.o \
omxtest_portreconfig_transit_2.o \
omxtest_portreconfig_transit_3.o \
omxtest_reposition.o \
omxtest_usebuffer.o \
omxtest_without_marker.o
#libomxde.so : $(OBJECT)
omxde : $(OBJECT)
$(cc) $(SDFLAGS) -o $@ $(CRT_OBJS)
omx_threadsafe_callbacks.o:src/omx_threadsafe_callbacks.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omx_threadsafe_callbacks.cpp
omxdectest.o:src/omxdectest.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxdectest.cpp
omxdectestbase.o:src/omxdectestbase.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxdectestbase.cpp
omxtest_corrupt_nal.o:src/omxtest_corrupt_nal.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_corrupt_nal.cpp
omxtest_buffer_busy.o:src/omxtest_buffer_busy.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_buffer_busy.cpp
omxtest_dynamic_reconfig.o:src/omxtest_dynamic_reconfig.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_dynamic_reconfig.cpp
omxtest_eos_missing.o:src/omxtest_eos_missing.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_eos_missing.cpp
omxtest_extra_partialframes.o:src/omxtest_extra_partialframes.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_extra_partialframes.cpp
omxtest_flush_eos.o:src/omxtest_flush_eos.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_flush_eos.cpp
omxtest_flush_port.o:src/omxtest_flush_port.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_flush_port.cpp
omxtest_get_role.o:src/omxtest_get_role.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_get_role.cpp
omxtest_incomplete_nal.o:src/omxtest_incomplete_nal.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_incomplete_nal.cpp
omxtest_missing_nal.o:src/omxtest_missing_nal.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_missing_nal.cpp
omxtest_multiple_instance.o:src/omxtest_multiple_instance.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_multiple_instance.cpp
omxtest_param_negotiation.o:src/omxtest_param_negotiation.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_param_negotiation.cpp
omxtest_partialframes.o:src/omxtest_partialframes.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_partialframes.cpp
omxtest_pause_resume.o:src/omxtest_pause_resume.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_pause_resume.cpp
omxtest_portreconfig_transit_1.o:src/omxtest_portreconfig_transit_1.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_portreconfig_transit_1.cpp
omxtest_portreconfig_transit_2.o:src/omxtest_portreconfig_transit_2.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_portreconfig_transit_1.cpp
omxtest_portreconfig_transit_3.o:src/omxtest_portreconfig_transit_3.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_portreconfig_transit_1.cpp
omxtest_reposition.o:src/omxtest_reposition.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_reposition.cpp
omxtest_usebuffer.o:src/omxtest_usebuffer.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_usebuffer.cpp
omxtest_without_marker.o:src/omxtest_without_marker.cpp
$(cc) $(CFLAGS) $(SDFLAGS) -c src/omxtest_without_marker.cpp
clean:
rm -rf *.o
