android - 处理异步任务返回的数据 (Firebase)

Question

我想弄清楚如何处理从 AsyncTask 返回的数据。

我有一个 Activity ，我正在调用异步 Firebase get 操作(不同类中存在的操作)，我想用检索到的 ArrayList 的大小更新 Activity 中存在的 TextView .这是在 Activity onCreate 中调用的我的 Firebase 调用:

public void getAttendants() {

   ArrayList<AttendModel> attendees = new ArrayList<AttendModel>();
    FirebaseConnection.getInstance().getAllAttendeesFor(uuid, attendees);

    Log.d("attendees", String.valueOf(attendees.size()));
}

这是我的 Firebase 操作:

 public void getAllAttendeesFor(String UUID, final ArrayList<AttendModel> attendArray) {
    final DatabaseReference attendObjects = getDatabaseTableWith(Constants.tableAttendObject);

    Query queryRef = attendObjects.orderByChild(Constants.taAttendObjectUUID).equalTo(UUID);

    queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                HashMap<String, Object> attend = (HashMap<String, Object>) postSnapshot.getValue();
                String UUID = (String) attend.get(Constants.taAttendObjectUUID);
                String userUsername = (String) attend.get(Constants.AttendObjectUserUsername);

                AttendModel attendModel = new AttendModel(userUsername, UUID);
                attendArray.add(attendModel);

 //here would like to notify or somehow return the attendArray
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}

在 Android 中最好的方法是什么？是否有可能实现某种适配器或完成处理程序？

Answer 1

您正在寻找的是回调接口(interface)，至于您的需求，您需要使用单个参数实现单个方法的简单接口(interface)，因为 Java 6(Android Java 版本)没有开箱即用的约定，您可以轻松创建它自己:

interface Callback {

void act(List<AttendModel> models);
}

将其作为参数传递给 firebase 包装方法，并使用结果调用它。

public void getAllAttendeesFor(String UUID, final ArrayList<AttendModel> attendArray, final Callback callback) {
    final DatabaseReference attendObjects = getDatabaseTableWith(Constants.tableAttendObject);

    Query queryRef = attendObjects.orderByChild(Constants.taAttendObjectUUID).equalTo(UUID);

    queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                HashMap<String, Object> attend = (HashMap<String, Object>) postSnapshot.getValue();
                String UUID = (String) attend.get(Constants.AttendObjectUUID);
                String userUsername = (String) attend.get(Constants.AttendObjectUserUsername);

                AttendModel attendModel = new AttendModel(userUsername, UUID);
                attendArray.add(attendModel);

                callback.act(attendArray)
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}

然后在你的上层方法中:

public void getAttendants() {

   ArrayList<AttendModel> attendees = new ArrayList<AttendModel>();
    FirebaseConnection.getInstance().getAllAttendeesFor(uuid, attendees, 
        new Callable<List<AttendModel) {
          void act(List<AttendModel> attendees){
            //here you can update the UI
            Log.d("attendees", String.valueOf(attendees.size()));
          }
        };


}

请注意，只有在主线程上调用 firebase 查询的 onDataChange 方法时，您才能更新 UI。