如何在Java for Android中修改新创建的监听器中的外部布尔值
我有一个Android片段类，它有一个在单击按钮后在外部Firebase数据库上写入内容的方法。
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());
}
}
});
}
}
writingSuccessfull和writingNotSuccessfull。在显示的代码中，我得到了一个错误&变量‘WritingSuccessFull’是从内部类内部访问的，需要是最终的或有效的最终的
当我让Android Studio解决此问题时，代码如下所示：
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());
}
}
});
}
}
现在我可以执行代码了，但是布尔值不会更改，即使执行了侦听器中的代码。我也尝试了一下，在布尔变量前没有加上&最终&。但这并没有改变任何事情。我不能修改此监听程序中的布尔变量。但这是我需要做的事情，因为我想知道数据是否已成功写入数据库。
知道我为什么会遇到这个问题吗？如何解决它？我将感谢您的每条评论。
更新：以下是更新后的代码，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
问题在于onComplete方法的异步调用。更改布尔值的代码不会立即调用，因为它是在异步调用的onComplete方法中调用的。这意味着在我的示例中，onComplete方法中的代码是在10次While循环迭代之后调用的，而不是在循环期间调用的。现在最大的问题是如何在While循环期间调用onComplete方法中的任何代码。
更新：以下是运行代码时来自logcat的(相关)输出：
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
结果是该项在FireBase数据库中保存了10次。我想要的是尝试在Firebase数据库中存储该项目一次。如果这是成功的，循环应该停止，并且应该有一个祝酒词告诉它是成功的。如果不成功，则循环应尝试10次(延迟1秒)。如果尝试10次后仍无法将该项目存储在FireBase数据库中，则应停止循环，并且应显示一条吐司消息，告知无法存储该项目。
解决方案
创建扩展Android视图模型的自定义类
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义视图模型类来观察值的更改
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());
}
}
});
}
}
这是MVVM体系结构的一个简单片段。希望它现在起作用了。谢谢。
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