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！