本文介紹了如何在Java for Android中修改新創(chuàng)建的監(jiān)聽(tīng)器中的外部布爾值的處理方法，對(duì)大家解決問(wèn)題具有一定的參考價(jià)值，需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)吧！
問(wèn)題描述
我有一個(gè)Android片段類，它有一個(gè)在單擊按鈕后在外部Firebase數(shù)據(jù)庫(kù)上寫入內(nèi)容的方法。
public class FR_Fragment extends Fragment implements View.OnClickListener {
public void onClick(View view) {
boolean writingSuccessfull = false;
boolean writingNotSuccessfull = false;
firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
writingSuccessfull = true;
writingNotSuccessfull = false;
Log.e("dbTAG", "Data successfully written.");
}
else {
writingSuccessfull = false;
writingNotSuccessfull = true;
Log.e("dbTAG", task.getException().getMessage());
}
}
});
}
}
但是，我不知何故無(wú)法訪問(wèn)我在OnCompleteListener的onClick方法中定義的布爾變量writingSuccessfull和writingNotSuccessfull。在顯示的代碼中，我得到了一個(gè)錯(cuò)誤&變量‘WritingSuccessFull’是從內(nèi)部類內(nèi)部訪問(wèn)的，需要是最終的或有效的最終的
當(dāng)我讓Android Studio解決此問(wèn)題時(shí)，代碼如下所示：
public class FR_Fragment extends Fragment implements View.OnClickListener {
public void onClick(View view) {
final boolean[] writingSuccessfull = { false };
final boolean[] writingNotSuccessfull = { false };
firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
writingSuccessfull[0] = true;
writingNotSuccessfull[0] = false
Log.e("dbTAG", "Data successfully written.");
}
else {
writingSuccessfull[0] = false;
writingNotSuccessfull[0] = true
Log.e("dbTAG", task.getException().getMessage());
}
}
});
}
}
現(xiàn)在我可以執(zhí)行代碼了，但是布爾值不會(huì)更改，即使執(zhí)行了偵聽(tīng)器中的代碼。我也嘗試了一下，在布爾變量前沒(méi)有加上&最終&。但這并沒(méi)有改變?nèi)魏问虑椤Ｎ也荒苄薷拇吮O(jiān)聽(tīng)程序中的布爾變量。但這是我需要做的事情，因?yàn)槲蚁胫罃?shù)據(jù)是否已成功寫入數(shù)據(jù)庫(kù)。
知道我為什么會(huì)遇到這個(gè)問(wèn)題嗎？如何解決它？我將感謝您的每條評(píng)論。
更新：以下是更新后的代碼，其中包含Volatile和AericBoolas：
public class FR_Fragment extends Fragment implements View.OnClickListener {
private volatile AtomicBoolean writingOrderToTheDatabaseWasSuccessful;
private volatile AtomicBoolean writingOrderToTheDatabaseWasNotSuccessful;
...
public void onClick(View view) {
int internalCounterAttempsWriteDataInTheFBDatabase =0;
writingOrderToTheDatabaseWasSuccessful = new AtomicBoolean (false);
writingOrderToTheDatabaseWasNotSuccessful = new AtomicBoolean (false);
while(writingOrderToTheDatabaseWasSuccessful.get() == false && writingOrderToTheDatabaseWasNotSuccessful.get()==false) {
internalCounterAttempsWriteDataInTheFBDatabase++;
Log.e("LogTag", "internalCounterAttempsWriteDataInTheFBDatabase: " +internalCounterAttempsWriteDataInTheFBDatabase );
Log.e("LogTag", "writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
Log.e("LogTag", "writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());
DatabaseReference rootRef = FirebaseDatabase.getInstance("https://drink-server-db-default-rtdb.europe-west1.firebasedatabase.app").getReference();
DatabaseReference ordersRef = rootRef.child("orders");
String id =...;
FirebaseDBItem_Order currentOrder = ...;
ordersRef.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
writingOrderToTheDatabaseWasSuccessful.set(true);
writingOrderToTheDatabaseWasNotSuccessful.set(false);
Log.e("dbTAG", "Data successfully written.");
Log.e("LogTag", "Listener: writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
Log.e("LogTag", "Listener: writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());
} else {
Log.e("dbTAG", task.getException().getMessage());
}
}//end method onComplete
});//end addOnCompleteListener
if (internalCounterAttempsWriteDataInTheFBDatabase >=10) {
writingOrderToTheDatabaseWasNotSuccessful.set(true);
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}//end while loop
Log.e("LogTag", "EndWhile: writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
Log.e("LogTag", "EndWhile: writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());
//Show a toast about the order
if (writingOrderToTheDatabaseWasSuccessful.get() ==true) {
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(getContext(), getString(R.string.message_orderSubmittedSuccessfully), duration);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
}
if (writingOrderToTheDatabaseWasNotSuccessful.get() ==true) {
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(getContext(), getString(R.string.message_orderSubmittedNotSuccessfully), duration);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
}
Navigation.findNavController(...);
}//end method onClick
}//end class
問(wèn)題在于onComplete方法的異步調(diào)用。更改布爾值的代碼不會(huì)立即調(diào)用，因?yàn)樗窃诋惒秸{(diào)用的onComplete方法中調(diào)用的。這意味著在我的示例中，onComplete方法中的代碼是在10次While循環(huán)迭代之后調(diào)用的，而不是在循環(huán)期間調(diào)用的。現(xiàn)在最大的問(wèn)題是如何在While循環(huán)期間調(diào)用onComplete方法中的任何代碼。
更新：以下是運(yùn)行代碼時(shí)來(lái)自logcat的(相關(guān))輸出：
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 1
writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 2
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 3
writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 4
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 5
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 6
writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 7
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 8
writingOrderToTheDatabaseWasSuccessful: false
E/LogTag: writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 9
writingOrderToTheDatabaseWasSuccessful: false
writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 10
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
E/LogTag: writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: EndWhile: writingOrderToTheDatabaseWasSuccessful: false
EndWhile: writingOrderToTheDatabaseWasNotSuccessful: true
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
Listener: writingOrderToTheDatabaseWasNotSuccessful: false
結(jié)果是該項(xiàng)在FireBase數(shù)據(jù)庫(kù)中保存了10次。我想要的是嘗試在Firebase數(shù)據(jù)庫(kù)中存儲(chǔ)該項(xiàng)目一次。如果這是成功的，循環(huán)應(yīng)該停止，并且應(yīng)該有一個(gè)祝酒詞告訴它是成功的。如果不成功，則循環(huán)應(yīng)嘗試10次(延遲1秒)。如果嘗試10次后仍無(wú)法將該項(xiàng)目存儲(chǔ)在FireBase數(shù)據(jù)庫(kù)中，則應(yīng)停止循環(huán)，并且應(yīng)顯示一條吐司消息，告知無(wú)法存儲(chǔ)該項(xiàng)目。
推薦答案
創(chuàng)建擴(kuò)展Android視圖模型的自定義類
public class MyViewModel extends AndroidViewModel{
private MutableLiveData<Boolean> writingSuccessful=new MutableLiveData<>();
public MyViewModel(@NonNull Application application)
{
// you can do any other stuff here if you want
}
public void setBooleanWritingSuccessful(Boolean b)
{
writingSuccessful.setValue(b);
}
public LiveData<Boolean> getBooleanWritingSuccessful()
{
return writingSuccessful;
}
}
然后在片段中使用此自定義視圖模型類來(lái)觀察值的更改
public class FR_Fragment extends Fragment implements View.OnClickListener {
private MyViewModel myViewModel;
private boolean writingSuccessfull= false;
@Override
public void onCreate(Bundle savedInstanceState)
{
// your stuffs
// initialize viewmodel
myViewModel=new ViewModelProvider(this,ViewModelProvider.AndroidViewModelFactory.getInstance(getActivity().getApplication())).get(MyViewModel.class);
}
@Override
public void onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
// set your viewmodel for observing the changes in boolean values.
myViewModel.getBooleanWritingSuccessful().observe(getViewLifecycleOwner(),new Observer<Boolean>(){
@Override
public void onChanged(Boolean b)
{
// update your writingSuccessful variable here.
writingSuccessfull=b;
}
});
}
// In onClick update your viewmodel's mutablelivedata;
public void onClick(View view) {
...
firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
//writingSuccessfull=true;
//writingNotSuccessfull= false;
//update the viewmodel's mutableLiveData
myViewModel.setBooleanWritingSuccessful(true);
Log.e("dbTAG", "Data successfully written.");
} else {
//writingSuccessfull=false;
//writingNotSuccessfull= true;
//update the viewmodel's mutableLiveData
myViewModel.setBooleanWritingSuccessful(false);
Log.e("dbTAG", task.getException().getMessage());
}
}
});
}
}
這是MVVM體系結(jié)構(gòu)的一個(gè)簡(jiǎn)單片段。希望它現(xiàn)在起作用了。謝謝。
這篇關(guān)于如何在Java for Android中修改新創(chuàng)建的監(jiān)聽(tīng)器中的外部布爾值的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，
