在应用程序完成获取并将获取的数据传递给它之后，我应该如何启动一个新的 Activity？

Question

在我的应用程序中，我使用联系人数据库并使用 RecyclerView 显示这些联系人。当我点击一个联系人时，我想从数据库中的表中获取它的数据，并将它们加载到一个新的 Activity、ContactCard 中。我有一个 AsyncTask()，它获取与所选 contactId 匹配的 PhoneNumber 对象，但我还需要从其他表中检索 Address 和 Email 对象。

我希望能够在获取所有相关数据后启动 activity，我尝试在 activity 中使用联系人 RecyclerView 执行此操作，但是由于尚未获取数据，应用程序崩溃。

我可以使用意图调用新的 activity，但是如何确保在启动新的 activity（有效显示此数据）之前首先从不同的表中获取数据？

我的一些代码：

public class PhoneNumberRepository {

    private WorksideDatabase worksideDatabase;
    private List<PhoneNumber> returnedNumbers;
    private Context mContext;

    public PhoneNumberRepository(Context context) {
        String DB_NAME = "workside_database";
        worksideDatabase = Room.databaseBuilder(context, WorksideDatabase.class, DB_NAME).build();
        mContext = context;
    }

    public List<PhoneNumber> fetchPhoneNumbers(final int id) {

        new AsyncTask<Integer, Void, List<PhoneNumber>>() {
            @Override
            protected List<PhoneNumber> doInBackground(Integer... ids) {

                returnedNumbers = worksideDatabase.phoneNumberDao().getPhoneNumbersById(id);

                System.out.println(returnedNumbers);

                for (PhoneNumber pn : returnedNumbers) {
                    System.out.println("Number: " + pn.getPhoneNumber());
                }

                return returnedNumbers;
            }

            // This runs in UI when background thread finishes
            @Override
            protected void onPostExecute(List<PhoneNumber> result) {
                super.onPostExecute(result);

                System.out.println("Entered onPostExecute of fetchPhoneNumbers");

                //                for (PhoneNumber pn : result) {
                //                    Toast.makeText(mContext, pn + "", Toast.LENGTH_SHORT).show();
                //                }
            }
        }.execute();

        return returnedNumbers;
    }

    public List<PhoneNumber> getPhoneNumbers(int id) {
        return fetchPhoneNumbers(id);
    }
}

联系人片段：

     adapter.setOnItemClickListener(
                contact -> {
     Intent viewContact = new Intent(getActivity(), WorksideContactCard.class);
     viewContact.putExtra(WORKSIDE_CONTACT, contact);

     PhoneNumberRepository phoneNumberRepository =
         new PhoneNumberRepository(getActivity().getApplicationContext());

     List<PhoneNumber> phoneNumberList;

     phoneNumberList = phoneNumberRepository.getPhoneNumbers(contact.getId());

     ArrayList<PhoneNumber> arrlistPhoneNumbers =
                                new ArrayList<>(phoneNumberList);
                        viewContact.putParcelableArrayListExtra(
                                WORKSIDE_CONTACT_PHONE_NO, arrlistPhoneNumbers);

      startActivity(viewContact);
}

Answer 1

在 doInBackground() 方法中将联系人存储在一个列表中，并在 activity 中启动新的意图onPostExecute() 方法并以此意图将联系人列表作为 intent.extra() 变量传递，检索并在称为 activity.

Answer 2

将您的存储库 class 更改为类似这样的内容

public class PhoneNumberRepository {

    private WorksideDatabase worksideDatabase;
    private List<PhoneNumber> returnedNumbers;
    private Context mContext;
    private boolean dataDownloaded;

    public PhoneNumberRepository(Context context) {
        String DB_NAME = "workside_database";
        worksideDatabase = Room.databaseBuilder(context, WorksideDatabase.class, DB_NAME).build();
        mContext = context;
    }

    public List<PhoneNumber> fetchPhoneNumbers(final int id) {

        new AsyncTask<Integer, Void, List<PhoneNumber>>() {
            @Override
            protected List<PhoneNumber> doInBackground(Integer... ids) {

                returnedNumbers = worksideDatabase.phoneNumberDao().getPhoneNumbersById(id);

                System.out.println(returnedNumbers);

                for (PhoneNumber pn : returnedNumbers) {
                    System.out.println("Number: " + pn.getPhoneNumber());
                }

                return returnedNumbers;
            }

            // This runs in UI when background thread finishes
            @Override
            protected void onPreExecute(List<PhoneNumber> result) {
                //set flag to false when download starts
               dataDownloaded = false;
            } 

            // This runs in UI when background thread finishes
            @Override
            protected void onPostExecute(Object obj) {
                super.onPostExecute(result);

                //set flag to true once download completes, you can also check if response is null and update it accordingly 
                dataDownloaded = true;

                System.out.println("Entered onPostExecute of fetchPhoneNumbers");

                //                for (PhoneNumber pn : result) {
                //                    Toast.makeText(mContext, pn + "", Toast.LENGTH_SHORT).show();
                //                }
            }
        }.execute();

        return returnedNumbers;
    }

    public List<PhoneNumber> getPhoneNumbers(int id) {
        return fetchPhoneNumbers(id);
    }

    public boolean isDataDownloaded(int id) {
        return dataDownloaded;
    }
}

无论您的数据是否下载

，都请在onItemClick()中使用此功能

if(phoneNumberRepository.isDataDownloaded()) {
   //code to fetch data from phonenumberrepo and start activity
}

Answer 3

您可以在单击某个项目时执行此操作，像这样启动异步任务

 adapter.setOnItemClickListener(
                contact -> {
     PhoneNumberRepository phoneNumberRepository =
     new PhoneNumberRepository(getActivity().getApplicationContext());

 List<PhoneNumber> phoneNumberList;

 phoneNumberRepository.getPhoneNumbers(contact.getId());

}

并将您的电话号码存储库更改为此class

public class PhoneNumberRepository {

        private WorksideDatabase worksideDatabase;
        private List<PhoneNumber> returnedNumbers;
        private Context mContext;

        public PhoneNumberRepository(Context context) {
            String DB_NAME = "workside_database";
            worksideDatabase = Room.databaseBuilder(context, WorksideDatabase.class, DB_NAME).build();
            mContext = context;
        }

        public void fetchPhoneNumbers(final int id) {

            new AsyncTask<Integer, Void, List<PhoneNumber>>() {
                @Override
                protected List<PhoneNumber> doInBackground(Integer... ids) {

                    returnedNumbers = worksideDatabase.phoneNumberDao().getPhoneNumbersById(id);

                    System.out.println(returnedNumbers);

                    for (PhoneNumber pn : returnedNumbers) {
                        System.out.println("Number: " + pn.getPhoneNumber());
                    }

                    return returnedNumbers;
                }

                // This runs in UI when background thread finishes
                @Override
                protected void onPostExecute(List<PhoneNumber> result) {
                    super.onPostExecute(result);
 Intent viewContact = new Intent(context, WorksideContactCard.class);
    ArrayList<PhoneNumber> arrlistPhoneNumbers =
                                new ArrayList<>(result);
                        viewContact.putParcelableArrayListExtra(
                                WORKSIDE_CONTACT_PHONE_NO, arrlistPhoneNumbers);

      context.startActivity(viewContact);
                    System.out.println("Entered onPostExecute of fetchPhoneNumbers");


                }
            }.execute();

        }

        public void getPhoneNumbers(int id) {
            return fetchPhoneNumbers(id);
        }
    }

在应用程序完成获取并将获取的数据传递给它之后，我应该如何启动一个新的 Activity？

How should I start a new Activity, after the application is done fetching and passing the fetched data to it?

java

android

database

android-intent

android-asynctask