新增LED設(shè)備--從上層到底層理解安卓架構(gòu)之JNI篇
[導(dǎo)讀]? ? ? ? ? ? 在上一篇中，我們已經(jīng)完成了HAL層的開發(fā)，那么framework層要如何調(diào)用它呢？答案是JNI(Java Native Interface)。JNI簡(jiǎn)單來(lái)說(shuō)就是java程序可以調(diào)用C/C++寫的動(dòng)態(tài)鏈接庫(kù)。JNI的存在使得底層可以以C代碼的形式實(shí)現(xiàn)，保持了高效率，上層又以java代碼的
JNI的實(shí)現(xiàn)
1.frameworks/base/services/core/jni/com_android_server_TestLedService.cpp
#define LOG_TAG "TestLedServiceJni"#include "jni.h"#include "JNIHelp.h"#include "android_runtime/AndroidRuntime.h"#include#include#include#include#includenamespace android{struct testled_device_t* testled_device = NULL;static void testled_setLed1(JNIEnv* env, jobject clazz, jint value) {int val = value;ALOGI("TestLed JNI: set value %d to led1.", val);if(!testled_device) {ALOGI("TestLed JNI: device is not open.");return;}if(val > 0){testled_device->control(0);//on}else{testled_device->control(1);//off}}static void testled_setLed2(JNIEnv* env, jobject clazz, jint value){int val = value;ALOGI("TestLed JNI: set value %d to led2.", val);if(!testled_device) {ALOGI("TestLed JNI: device is not open.");return;}if(val > 0){testled_device->control(2);//on}else{testled_device->control(3);//off}}static inline int testled_device_open(const hw_module_t* module, struct testled_device_t** device) {return module->methods->open(module, LED_HAL_MODULE_ID, (struct hw_device_t**)device);}static jboolean testled_init(JNIEnv* env, jclass clazz) {testled_module_t* module;ALOGI("TestLed JNI: initializing......");if(hw_get_module(LED_HAL_MODULE_ID, (const struct hw_module_t**)&module) == 0) {ALOGI("TestLed JNI: testled Stub found.");if(testled_device_open(&(module->common), &testled_device) == 0) {ALOGI("TestLed JNI: testled device is open.");//testled_device->open();return 0;}ALOGE("TestLed JNI: failed to open testled device.");return -1;}ALOGE("TestLed JNI: failed to get testled stub module.");return -1;}static const JNINativeMethod method_table[] = {{"testledinit_native", "()Z", (void*)testled_init},{"setled1_native", "(I)V", (void*)testled_setLed1},{"setled2_native", "(I)V", (void*)testled_setLed2},};int register_android_server_TestLedService(JNIEnv *env) {return jniRegisterNativeMethods(env, "com/android/server/TestLedService", method_table, NELEM(method_table));}};
2.frameworks/base/services/core/jni/onload.cpp
namespace中增加函數(shù)聲明
namespace android {……int register_android_server_TestLedService(JNIEnv *env);};JNI_OnLoad增加register_android_server_TestLedService的函數(shù)調(diào)用extern "C" jint JNI_OnLoad(JavaVM* vm, void* /* reserved */){…register_com_android_server_rkdisplay_RkDisplayModes(env);register_android_server_TestLedService(env);return JNI_VERSION_1_4;}
LOCAL_SRC_FILES += \……$(LOCAL_REL_DIR)/com_android_server_TestLedService.cpp \$(LOCAL_REL_DIR)/onload.cpp
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