android service 添加

一步：实现driver。Driver也就是service最终需要去控制的对象，这一步就不详细去说了，不管是写成字符型设备文件还块设备，或者是伪文件系统/proc的普通文件，只要能满足这种交互的目的就行。笔者那个字符型设备文件跟/proc普通文件的交互方法都做过，现在还是以字符型设备驱动为例吧。

 

        第二步：android用户空间调用drvier。在android架构中，这个大任当然是hal层当仁不让的。在hal层就要按照hw_module_t的架构去写。代码如下：

static int open_my_driver_device (const struct hw_module_t * module, char const * name, struct hw_device_t ** device){struct mydriver_context_t * dev = (struct mydriver_context_t *)malloc(sizeof(struct mydriver_context_t));memset(dev, 0, sizeof(struct mydriver_context_t));int fd = open("/dev/my_driver", O_RDONLY);if (fd < 0) {LOGE("failed to open my driver device!");return -1;}dev->fd = fd;dev->device.common.tag = HARDWARE_DEVICE_TAG;dev->device.common.version = 0;dev->device.common.module = (struct hw_module *)module;dev->device.common.close = (int (*)(struct hw_device_t*))close_my_driver_device;dev->device.get_acc_state = (int (*)(struct mydriver_device_t *, int *))get_ my_driver _state;*device = (struct hw_device_t *)dev;return 0;}static struct hw_module_methods_t my_driver_module_methods = {.open = open_my_driver_device,};const struct hw_module_t HAL_MODULE_INFO_SYM = {.tag = HARDWARE_MODULE_TAG,.version_major = 1,.version_minor = 0,.id = MY_DRIVER_HARDWARE_MODULE_ID,.name = "edsam my driver Module",.author = "edsam.",.methods = &my_driver_module_methods,};

第三步：可以直接去写JNI了。当然如果不是第二步也能合在这里一起写，但是这样代码架构就没那么完整。 JNI怎么写就去查一下相关文档。JNI代码放置/frameworks/base/services/jni/下：

static jint init_native(JNIEnv * env, jobject clazz)      {          int err;          hw_module_t * module;          struct my_driver_device_t * device;            device = NULL;            err = hw_get_module(MY_DRIVER_HARDWARE_MODULE_ID (hw_module_t const **)&module);            if (err == 0) {              hw_device_t * hw_device;              err = module->methods->open(module, NULL, &hw_device);                if (err != 0) {                  LOGE("module open fail!");                  return 0;              } else {                  device = (struct my_driver_device_t *)hw_device;              }          }            return (jint)device;      }        static jint get_my_driver_status_native (JNIEnv * env, jobject clazz, int ptr)      {          struct my_driver_device_t * device = (struct my_driver_device_t *)ptr;          int state = 0;          if (device) {              device->get_my_driver_status(device, &state);          }          return state;      }        static JNINativeMethod method_table[] = {          {"init_native", "()I", (void *)init_native },          {"finalize_native", "(I)V", (void *)finalize_native },          {"get_earphones_status_native", "(I)I", (void *)get_my_driver_status_native },      };        int register_android_server_MyDriverService(JNIEnv * env) {          return jniRegisterNativeMethods(env,              "com/android/server/MyDriverService",              method_table,              NELEM(method_table)              );      } 

第四步：注册service。在/frameworks/base/services/jni/目录下有个onload.cpp的文件添加register_android_server_MyDriverService (env);调用。

 

         第五步：java层添加service代码。在/frameworks/base/services/java/com/android/server/目录下添加。

package com.android.server;    import android.os.RemoteException;    import com.android.internal.os.IMyDriverService;    public class MyDriverService extends IMyDriverService.Stub {      private static final String TAG = "MyDriverService";      private static final boolean DEBUG = false;            @Override      public int getMyDriverState() throws RemoteException {                    return get_my_driver_status_native (mNativePointer);      }            public MyDriverService() {          mNativePointer = init_native();                }               protected void finalize() throws Throwable {          finalize_native(mNativePointer);          super.finalize();      }                  private static native int init_native();      private static native void finalize_native(int ptr);      private static native int getMyDriverState_native(int ptr);        private int mNativePointer;  }  

第六步：增加AIDL定义。文件放置/frameworks/base/core/java/com/android/internal/os/下，增加IMydriverService.aldl内容如下：

package com.android.internal.os;      interface IMyDriverService {          int getMyDriverState ();  }  

上面的aidl文件编译添加到/frameworks/base/Android.mk中定义的LOCAL_SRC_FILES中。

 

        第七步：在systemserver里注册。frameworks/base/services/java/com/android/server/SystemServer.java中的run方法里增加：

            mydriverService = newMyDriverService();

            ServiceManager.addService(Context.MY_DRIVER_SERVICE, mydriverService);

 

        第八步：产生Manager对象。在/frameworks/base/core/java/android/app/下添加有个MyDriverManager.java，

package android.app;    import android.content.Context;  import android.os.RemoteException;  import android.os.ServiceManager;  import android.util.Slog;    import com.android.internal.os.IMyDriverService;      public class MyDriverManager {      private static final String TAG = "MyDriverManager";      private static final boolean DEBUG = false;                private IMyDriverService mService = null;            public MyDriverManager() {                }            private synchronized IMyDriverService getService() {          if (mService == null) {              mService = IMyDriverService.Stub.asInterface(                      ServiceManager.getService(Context.MY_DRIVER_SERVICE));              if (mService == null) {                  Slog.w(TAG, "warning : no MyDriverService ");              }          }          return mService;      }            public int getMyDriverStatus() {          try {              final IMyDriverService svc = getService();              if (svc != null) {                  return svc. getMyDriverState();              } else {                  Slog.e(TAG, "error : IMyDriverService not exist!");                  throw new RuntimeException("IMyDriverService not exist!");              }          } catch (RemoteException e) {              Slog.e(TAG, "error : getEarPhonesStatus remote error!");              throw new RuntimeException(e);          }                }        }  } 

在/frameworks/base/core/java/android/content/Context中定义MY_DRIVER_SERVICE字符串，在/frameworks/base/core/java/android/app/ContextImpl.java中：

registerService(MY_DRIVER_SERVICE, new ServiceFetcher() {              public Object getService(ContextImpl ctx) {                  return new MY_DRIVER_Manager();              }          });  

第九步：在编译的时候执行make update-api。就会把新的api加入到api/current.txt文件中去。

        最后一步：当然是在需要的地方调用了。

MY_DRIVER_Manager mydriverService = (MY_DRIVER_Manager)getSystemService(Context. MY_DRIVER_Manager);                              if (mydriverService!= null) {                                  mydriverService. getMyDriverStatus ();                              }                          } 

通过以上步骤，完整编译一下系统，应该service能正常工作起来了。加一个service还是挺麻烦的，上层的互联关系比较多。

        没有高深的理论介绍，只有简单的实践步骤，比较详细的介绍了一个service的来龙去脉，有兴趣就自己动手实践一下，相信会有收获的。Service在开发中用得非常广泛，号称四大组件之一，真的是名不虚传！征服它，驾驭它，为我所用，为做出好的android产品服务！