【Android Training - 15】云同步的实现 [Lesson 1 - 使用App Engine进行同步]

Syncing with App Engine [使用App Engine进行同步]

Prepare Your Environment [准备你的开发环境]

Create Your Projects [创建你的项目]

Create the Data Layer [创建数据层]

package com.cloudtasks.server;

import javax.persistence.*;

@Entity
public class Task {

    private String emailAddress;
    private String name;
    private String userId;
    private String note;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    public Task() {
    }

    public String getEmailAddress() {
        return this.emailAddress;
    }

    public Long getId() {
        return this.id;
    }
    ...
}

Entity

Id

GeneratedValue

Entity

Id

GeneratedValue分别表明了寻找这个类的id与这个id是如何形成的(在上面的示例中，

GenerationType.IDENTITY意味这是由DB生成的

@Entity的方法来实现的

Create the Persistence Layer [创建持久层]

/**
* Remove this object from the data store.
*/
public void delete(Long id) {
    PersistenceManager pm = PMF.get().getPersistenceManager();
    try {
        Task item = pm.getObjectById(Task.class, id);
        pm.deletePersistent(item);
    } finally {
        pm.close();
    }
}

public Task find(Long id) {
    if (id == null) {
        return null;
    }

    PersistenceManager pm = PMF.get().getPersistenceManager();
    try {
        Query query = pm.newQuery("select from " + Task.class.getName()
        + " where id==" + id.toString() + " && emailAddress=='" + getUserEmail() + "'");
        List list = (List) query.execute();
        return list.size() == 0 ? null : list.get(0);
    } catch (RuntimeException e) {
        System.out.println(e);
        throw e;
    } finally {
        pm.close();
    }
}

Query and Update from the Android App [从Android App查询与更新]

AsyncTask中来完成的，这样不会因为网络操作而卡到

public void fetchTasks (Long id) {
  // Request is wrapped in an AsyncTask to avoid making a network request
  // on the UI thread.
    new AsyncTask>() {
        @Override
        protected List doInBackground(Long... arguments) {
            final List list = new ArrayList();
            MyRequestFactory factory = Util.getRequestFactory(mContext,
            MyRequestFactory.class);
            TaskRequest taskRequest = factory.taskNinjaRequest();

            if (arguments.length == 0 || arguments[0] == -1) {
                factory.taskRequest().queryTasks().fire(new Receiver>() {
                    @Override
                    public void onSuccess(List arg0) {
                      list.addAll(arg0);
                    }
                });
            } else {
                newTask = true;
                factory.taskRequest().readTask(arguments[0]).fire(new Receiver() {
                    @Override
                    public void onSuccess(TaskProxy arg0) {
                      list.add(arg0);
                    }
                });
            }
        return list;
    }

    @Override
    protected void onPostExecute(List result) {
        TaskNinjaActivity.this.dump(result);
    }

    }.execute(id);
}
...

public void dump (List tasks) {
    for (TaskProxy task : tasks) {
        Log.i("Task output", task.getName() + "\n" + task.getNote());
    }
}

new AsyncTask() {
    @Override
    protected Void doInBackground(Void... arg0) {
        MyRequestFactory factory = (MyRequestFactory)
                Util.getRequestFactory(TasksActivity.this,
                MyRequestFactory.class);
        TaskRequest request = factory.taskRequest();

        // Create your local proxy object, populate it
        TaskProxy task = request.create(TaskProxy.class);
        task.setName(taskName);
        task.setNote(taskDetails);
        task.setDueDate(dueDate);

        // To the cloud!
        request.updateTask(task).fire();
        return null;
    }
}.execute();

Configure the C2DM Server-Side [确认C2DM服务器端]

public static Task updateTask(Task task) {
    task.setEmailAddress(DataStore.getUserEmail());
    task = db.update(task);
    DataStore.sendC2DMUpdate(TaskChange.UPDATE + TaskChange.SEPARATOR + task.getId());
    return task;
}

// Helper method.  Given a String, send it to the current user's device via C2DM.
public static void sendC2DMUpdate(String message) {
    UserService userService = UserServiceFactory.getUserService();
    User user = userService.getCurrentUser();
    ServletContext context = RequestFactoryServlet.getThreadLocalRequest().getSession().getServletContext();
    SendMessage.sendMessage(context, user.getEmail(), message);
}

TaskChange，创建了一些常量

public class TaskChange {
    public static String UPDATE = "Update";
    public static String DELETE = "Delete";
    public static String SEPARATOR = ":";
}

Configure the C2DM Client-Side [确认C2DM的客户端]

C2DMReceiver类

onMessage()

//In your C2DMReceiver class

public void notifyListener(Intent intent) {
    if (listener != null) {
        Bundle extras = intent.getExtras();
        if (extras != null) {
            String message = (String) extras.get("message");
            String[] messages = message.split(Pattern.quote(TaskChange.SEPARATOR));
            listener.onTaskUpdated(messages[0], Long.parseLong(messages[1]));
        }
    }
}

// Elsewhere in your code, wherever it makes sense to perform local updates
public void onTasksUpdated(String messageType, Long id) {
    if (messageType.equals(TaskChange.DELETE)) {
        // Delete this task from your local data store
        ...
    } else {
        // Call that monstrous Asynctask defined earlier.
        fetchTasks(id);
    }
}