在应用程序获取并将获取的数据传递给它之后，我应该如何启动新的"活动"

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DB中的表中获取其数据，并将它们加载到一个新的活动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该活动，并尝试在使用ContactsRecyclerView的活动中这样做，但由于数据尚未获取，应用程序崩溃。

我可以使用意向调用新活动，但在开始新活动(有效地显示这些数据(之前，如何确保首先从不同表中提取数据？

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：

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

当你点击一个项目时，你可以这样做，启动像这样的

adapter.setOnItemClickListener(
contact -> {
PhoneNumberRepository phoneNumberRepository =
new PhoneNumberRepository(getActivity().getApplicationContext());
List<PhoneNumber> phoneNumberList;
phoneNumberRepository.getPhoneNumbers(contact.getId());
}

并将您的PhoneNumberRepository更改为此类

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);
}
}

Answer 2

将联系人存储在doInBackground((方法中的列表中，并在onPostExecute((

Answer 3

将存储库类更改为类似的类

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;
}
}

在onItemClick()中使用此功能，无论您的数据是否已下载

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