我开始学习 Android NDK。我对 C/C++ 编码了解不多,想开始。我导入了简单的 HelloJni 示例,并一直在弄乱这个来学习和文档。我被卡住了,觉得这可能是我使用 Android.mk 的方式。看起来是正确的,但是构建在我正在测试的第二个模块上不起作用。这是我在
<project folder>/jni/
HelloJni.cpp
Android.mk
Application.mk
mytools/
simplemath.h
simplemath.cpp
我想用我的 java 调用 HelloJni.cpp 中的一个方法,该方法又调用 simplemath.cpp 中的一个方法并返回一个值。简单的测试只是结转从 simplemath 添加的数字。
下面是我所有的来源
--------------------Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := HelloJni
LOCAL_SRC_FILES := HelloJni.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
TOOLS_DIR := $(LOCAL_PATH)/mytools
LOCAL_C_INCLUDES := $(TOOLS_DIR)
LOCAL_MODULE := simplemath
LOCAL_SRC_FILES := $(TOOLS_DIR)/simplemath.cpp
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog
include $(BUILD_SHARED_LIBRARY)
--------------------HelloJni.cpp
#include <stl/_istream.h>
#include <stl/_string.h>
#include <stl/_string_fwd.h>
#define DEBUG_TAG "JNI Native Code..."
using namespace std;
extern "C" {
JNIEXPORT jstring JNICALL Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env, jobject thiz, jstring str){
simplemath mathTools;
mathTools.add(4, 5);
.....
return env->NewStringUTF(str);
}
};
--------------------simplemath.h
#ifdef __cplusplus
extern "C" {
#endif
#define SIMPLEMATH_H
namespace std {
class simplemath{
public:
simplemath();
int add(int, int);
~simplemath();
};
}
#ifdef __cplusplus
}
#endif
----------------simplemath.cpp
#include <simplemath.h>
namespace std {
simplemath::simplemath(){
}
int simplemath::add(int a, int b){
return a + b;
}
simplemath::~simplemath(){
}
}
当我对项目进行清理时,没有出现任何错误。构建后,我得到以下信息:
"Compile++ thumb : HelloJni <= HelloJni.cpp
Prebuilt : libstlport_static.a <= <NDK>/sources/cxx-stl/stlport/libs/armeabi/
SharedLibrary : libHelloJni.so
C:/Users/Geek/android-ndk-r8d/toolchains/arm-linux-androideabi-4.6/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/4.6/../../../../arm-linux-androideabi/bin/ld.exe: ./obj/local/armeabi/objs/HelloJni/HelloJni.o: in function Java_com_example_hellojni_HelloJni_stringFromJNI:jni/HelloJni.cpp:88: error: undefined reference to 'std::simplemath::simplemath()'
C:/Users/Geek/android-ndk-r8d/toolchains/arm-linux-androideabi-4.6/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/4.6/../../../../arm-linux-androideabi/bin/ld.exe: ./obj/local/armeabi/objs/HelloJni/HelloJni.o: in function Java_com_example_hellojni_HelloJni_stringFromJNI:jni/HelloJni.cpp:89: error: undefined reference to 'std::simplemath::add(int, int)'
C:/Users/Geek/android-ndk-r8d/toolchains/arm-linux-androideabi-4.6/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/4.6/../../../../arm-linux-androideabi/bin/ld.exe: ./obj/local/armeabi/objs/HelloJni/HelloJni.o: in function Java_com_example_hellojni_HelloJni_stringFromJNI:jni/HelloJni.cpp:92: error: undefined reference to 'std::simplemath::~simplemath()'
collect2: ld returned 1 exit status
make: *** [obj/local/armeabi/libHelloJni.so] Error 1
最佳答案
您还没有声明模块之间的任何依赖关系,请使用 LOCAL_SHARED_LIBRARIES
来声明:
LOCAL_PATH := $(call my-dir)
TOOLS_DIR := $(LOCAL_PATH)/mytools
include $(CLEAR_VARS)
LOCAL_C_INCLUDES := $(TOOLS_DIR)
LOCAL_EXPORT_C_INCLUDES := $(TOOLS_DIR)
LOCAL_MODULE := simplemath
LOCAL_SRC_FILES := $(TOOLS_DIR)/simplemath.cpp
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := HelloJni
LOCAL_SRC_FILES := HelloJni.cpp
LOCAL_SHARED_LIBRARIES := simplemath
LOCAL_LDLIBS := -llog
include $(PREBUILT_SHARED_LIBRARY)
关于Android NDK JNI 未定义对 C++ 源方法的引用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32187660/