Android模拟器学framework和driver之battery backlight-----2. battery in jni

上篇介绍了模拟器的内核goldfish中的battery模块，也介绍了power_supply是如何工作的，一般我自己写驱动也差不多是这个流程，驱动抄着抄着自己就熟悉了，呵呵，记得之前我问过一个前辈，驱动要怎么学习，她说：抄代码先！！！

废话不多扯，这里介绍android jni层是如何处理battery的信息的。

上一篇中讲到在driver中做的事情对我们user有用的就只有2件事情，一是当battery信息发生变化的时候会给用户层发送一个uevent，二是在在文件系统中生成了battery信息的文件，包括电池电量，电池状态灯信息。

这里介绍中间层jni，主要封装读取battery信息的函数，代码位置：android2.3.3/frameworks/base/services/jni/com_android_server_BatteryService.cpp

这里做的事情比较简单：

1. 找到文件系统中我们生成的battery信息的文件路径

2. 找到我们java文件中用到中battery信息相关的类

3. 得到我们java文件中定义的battery信息的变量的fieldID

4.  读取文件系统中相应的battery 信息的文件，通过fieldID给java中的变量赋值，进行battery状态的更新。

1. 找到文件系统中我们生成的battery信息的文件路径

DIR* dir = opendir(POWER_SUPPLY_PATH); if (dir == NULL) { LOGE("Could not open %s\n", POWER_SUPPLY_PATH); return -1; } while ((entry = readdir(dir))) { const char* name = entry->d_name; // ignore "." and ".." if (name[0] == '.' && (name[1] == 0 || (name[1] == '.' && name[2] == 0))) { continue; } char buf[20]; // Look for "type" file in each subdirectory snprintf(path, sizeof(path), "%s/%s/type", POWER_SUPPLY_PATH, name); int length = readFromFile(path, buf, sizeof(buf)); if (length > 0) { if (buf[length - 1] == '\n') buf[length - 1] = 0; if (strcmp(buf, "Mains") == 0) { snprintf(path, sizeof(path), "%s/%s/online", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.acOnlinePath = strdup(path); } else if (strcmp(buf, "USB") == 0) { snprintf(path, sizeof(path), "%s/%s/online", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.usbOnlinePath = strdup(path); } else if (strcmp(buf, "Battery") == 0) { snprintf(path, sizeof(path), "%s/%s/status", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryStatusPath = strdup(path); snprintf(path, sizeof(path), "%s/%s/health", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryHealthPath = strdup(path); snprintf(path, sizeof(path), "%s/%s/present", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryPresentPath = strdup(path); snprintf(path, sizeof(path), "%s/%s/capacity", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryCapacityPath = strdup(path); snprintf(path, sizeof(path), "%s/%s/voltage_now", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) { gPaths.batteryVoltagePath = strdup(path); // voltage_now is in microvolts, not millivolts gVoltageDivisor = 1000; } else { snprintf(path, sizeof(path), "%s/%s/batt_vol", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryVoltagePath = strdup(path); } snprintf(path, sizeof(path), "%s/%s/temp", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) { gPaths.batteryTemperaturePath = strdup(path); } else { snprintf(path, sizeof(path), "%s/%s/batt_temp", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryTemperaturePath = strdup(path); } snprintf(path, sizeof(path), "%s/%s/technology", POWER_SUPPLY_PATH, name); if (access(path, R_OK) == 0) gPaths.batteryTechnologyPath = strdup(path); } } } closedir(dir); if (!gPaths.acOnlinePath) LOGE("acOnlinePath not found"); if (!gPaths.usbOnlinePath) LOGE("usbOnlinePath not found"); if (!gPaths.batteryStatusPath) LOGE("batteryStatusPath not found"); if (!gPaths.batteryHealthPath) LOGE("batteryHealthPath not found"); if (!gPaths.batteryPresentPath) LOGE("batteryPresentPath not found"); if (!gPaths.batteryCapacityPath) LOGE("batteryCapacityPath not found"); if (!gPaths.batteryVoltagePath) LOGE("batteryVoltagePath not found"); if (!gPaths.batteryTemperaturePath) LOGE("batteryTemperaturePath not found"); if (!gPaths.batteryTechnologyPath) LOGE("batteryTechnologyPath not found");
2. 找到我们java文件中用到中battery信息相关的类

jclass clazz = env->FindClass("com/android/server/BatteryService"); if (clazz == NULL) { LOGE("Can't find com/android/server/BatteryService"); return -1; }
3. 得到我们java文件中定义的battery信息的变量的fieldID

gFieldIds.mAcOnline = env->GetFieldID(clazz, "mAcOnline", "Z"); gFieldIds.mUsbOnline = env->GetFieldID(clazz, "mUsbOnline", "Z"); gFieldIds.mBatteryStatus = env->GetFieldID(clazz, "mBatteryStatus", "I"); gFieldIds.mBatteryHealth = env->GetFieldID(clazz, "mBatteryHealth", "I"); gFieldIds.mBatteryPresent = env->GetFieldID(clazz, "mBatteryPresent", "Z"); gFieldIds.mBatteryLevel = env->GetFieldID(clazz, "mBatteryLevel", "I"); gFieldIds.mBatteryTechnology = env->GetFieldID(clazz, "mBatteryTechnology", "Ljava/lang/String;"); gFieldIds.mBatteryVoltage = env->GetFieldID(clazz, "mBatteryVoltage", "I"); gFieldIds.mBatteryTemperature = env->GetFieldID(clazz, "mBatteryTemperature", "I");

4.  读取文件系统中相应的battery 信息的文件，通过fieldID给java中的变量赋值，进行battery状态的更新。

static void android_server_BatteryService_update(JNIEnv* env, jobject obj) { setBooleanField(env, obj, gPaths.acOnlinePath, gFieldIds.mAcOnline); setBooleanField(env, obj, gPaths.usbOnlinePath, gFieldIds.mUsbOnline); setBooleanField(env, obj, gPaths.batteryPresentPath, gFieldIds.mBatteryPresent); setIntField(env, obj, gPaths.batteryCapacityPath, gFieldIds.mBatteryLevel); setVoltageField(env, obj, gPaths.batteryVoltagePath, gFieldIds.mBatteryVoltage); setIntField(env, obj, gPaths.batteryTemperaturePath, gFieldIds.mBatteryTemperature); const int SIZE = 128; char buf[SIZE]; if (readFromFile(gPaths.batteryStatusPath, buf, SIZE) > 0) env->SetIntField(obj, gFieldIds.mBatteryStatus, getBatteryStatus(buf)); else env->SetIntField(obj, gFieldIds.mBatteryStatus, gConstants.statusUnknown); if (readFromFile(gPaths.batteryHealthPath, buf, SIZE) > 0) env->SetIntField(obj, gFieldIds.mBatteryHealth, getBatteryHealth(buf)); if (readFromFile(gPaths.batteryTechnologyPath, buf, SIZE) > 0) env->SetObjectField(obj, gFieldIds.mBatteryTechnology, env->NewStringUTF(buf)); }
具体代码自行分析，这边我推荐我的一个关于JNI的专栏，那里我写的比较详细，在jni是如何调用java中的成员变量和成员函数的。

http://blog.csdn.net/column/details/jnijni.html

jni层介绍到这边，比较简单。