[英]Retrieving Data from FireStore using MVVM Architecture
我正在嘗試遵循Android體系結構原則,並希望您在FireStore數據庫的頂部實現它們。
目前,我有一個存儲庫Class
,用於處理所有帶有基礎數據的查詢。 我有一個需要從文檔中的字段中獲取鍵的Set<String>
的Fragment
,並且想知道檢索此數據的最佳方法是什么。 在我之前的問題中, Alex Mamo建議將Interface
與onCompleteListener
結合使用,因為從Firestore檢索數據是Asynchronous
。
這種方法似乎有效,但是我不確定如何從此Interface
提取數據到Fragment
局部變量。 如果我想使用這些數據,我的代碼是否必須在我對abstract
方法的定義之內?
如果要將數據從Firestore獲取到我的Fragment
我是否仍要遵循MVVM原理,我必須將片段中定義的Interface
對象作為參數傳遞給我的存儲庫?
這是使用存儲庫查詢Firestore數據庫的推薦方法嗎?
以下是調用ViewModel
檢索數據的Interface
和方法:
public interface FirestoreCallBack{
void onCallBack(Set<String> keySet);
}
public void testMethod(){
Log.i(TAG,"Inside testMethod.");
mData.getGroups(new FirestoreCallBack() {
//Do I have to define what I want to use the data for here (e.g. display the contents of the set in a textview)?
@Override
public void onCallBack(Set<String> keySet) {
Log.i(TAG,"Inside testMethod of our Fragment and retrieved: " + keySet);
myKeySet = keySet;
Toast.makeText(getContext(),"Retrieved from interface: "+ myKeySet,Toast.LENGTH_SHORT).show();
}
});
}
我在存儲庫上調用的ViewModel
方法:
private FirebaseRepository mRepository;
public void getGroups(TestGroupGetFragment.FirestoreCallBack firestoreCallBack){
Log.i(TAG,"Inside getGroups method of FirebaseUserViewModel");
mRepository.getGroups(firestoreCallBack);
}
最后,我的Repository方法query
我的FireStore數據庫:
public void getGroups(final TestGroupGetFragment.FirestoreCallBack firestoreCallBack){
Log.i(TAG,"Attempting to retrieve a user's groups.");
userCollection.document(currentUser.getUid()).get().addOnCompleteListener(
new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()){
DocumentSnapshot document = task.getResult();
Log.i(TAG,"Success inside the onComplete method of our document .get() and retrieved: "+ document.getData().keySet());
firestoreCallBack.onCallBack(document.getData().keySet());
} else {
Log.d(TAG,"The .get() failed for document: " + currentUser.getUid(), task.getException());
}
}
});
Log.i(TAG, "Added onCompleteListener to our document.");
}
已編輯
public void testMethod(){
Log.i(TAG,"Inside testMethod.");
mData.getGroups(new FirestoreCallBack() {
@Override
public void onCallBack(Set<String> keySet) {
Log.i(TAG,"Inside testMethod of our Fragment and retrieved: " + keySet);
myKeySet = keySet;
someOtherMethod(myKeySet); //I know I can simply pass keySet.
Toast.makeText(getContext(),"GOT THESE FOR YOU: "+ myKeySet,Toast.LENGTH_SHORT).show();
}
});
Log.i(TAG,"In testMethod, retrieving the keySet returned: "+ myKeySet);
}
例如,我只使用LiveData
而不是interface
將數據帶到recyclerview。
首先,我們必須創建Firestore query
。 在此示例中,我列出了集合中的所有文檔。
public class FirestoreLiveData<T> extends LiveData<T> {
public static final String TAG = "debinf firestore";
private ListenerRegistration registration;
private CollectionReference colRef;
private Class clazz;
public FirestoreLiveData(CollectionReference colRef, Class clazz) {
this.colRef = colRef;
this.clazz = clazz;
}
EventListener<QuerySnapshot> eventListener = new EventListener<QuerySnapshot>() {
@Override
public void onEvent(@Nullable QuerySnapshot queryDocumentSnapshots, @Nullable FirebaseFirestoreException e) {
if (e != null) {
Log.i(TAG, "Listen failed.", e);
return;
}
if (queryDocumentSnapshots != null && !queryDocumentSnapshots.isEmpty()) {
List<T> itemList = new ArrayList<>();
for (DocumentSnapshot snapshot : queryDocumentSnapshots.getDocuments()) {
T item = (T) snapshot.toObject(clazz);
itemList.add(item);
Log.i(TAG, "snapshot is "+snapshot.getId());
}
setValue((T) itemList);
}
}
};
@Override
protected void onActive() {
super.onActive();
registration = colRef.addSnapshotListener(eventListener);
}
@Override
protected void onInactive() {
super.onInactive();
if (!hasActiveObservers()) {
registration.remove();
registration = null;
}
}
}
接下來,我們在Repository
創建一個鏈接
public class Repository {
public Repository() {
}
public LiveData<List<ProductsObject>> productListening(GroupObject group) {
return new FirestoreLiveData<>(DatabaseRouter.getCollectionRef(group.getGroupCreator()).document(group.getGroupKey()).collection("ProductList"), ProductsObject.class);
}
}
之后,我們創建ViewModel
:
public class MyViewModel extends ViewModel {
Repository repository = new Repository();
public LiveData<List<ProductsObject>> getProductList(GroupObject groupObject) {
return repository.productListening(groupObject);
}
}
最后,在我們的MainActivity
或Fragment
我們觀察到Firestore中包含的數據:
viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
viewModel.getProductList(groupObject).observe(this, new Observer<List<ProductsObject>>() {
@Override
public void onChanged(@Nullable List<ProductsObject> productsObjects) {
//Log.i(TAG, "viewModel: productsObjects is "+productsObjects.get(0).getCode());
adapter.submitList(productsObjects);
}
});
希望對您有所幫助。
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