带有 Firebase 的 Android 架构组件，特别是 Firestore

Question

我正在经历这个blog通过 Doug Stevenson (Firebase 开发者倡导者)该博客讨论了如何将 firebase 实时数据库 与 android 架构组件一起使用。

FirebaseQueryLiveData 类构成了一个可重用的类，用于管理所有 Firebase 查询并实现 LiveData。虽然这完全适用于 Firebase RealTime 数据库，但我似乎无法更改或更改它以支持云 firestore 数据库。

这是代码

public class FirebaseQueryLiveData extends LiveData<DataSnapshot> {
    private static final String LOG_TAG = "FirebaseQueryLiveData";

    private final Query query;
    private final MyValueEventListener listener = new MyValueEventListener();

    public FirebaseQueryLiveData(Query query) {
        this.query = query;
    }

    public FirebaseQueryLiveData(DatabaseReference ref) {
        this.query = ref;
    }

    @Override
    protected void onActive() {
        Log.d(LOG_TAG, "onActive");
        query.addValueEventListener(listener);
    }

    @Override
    protected void onInactive() {
        Log.d(LOG_TAG, "onInactive");
        query.removeEventListener(listener);
    }

    private class MyValueEventListener implements ValueEventListener {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            setValue(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.e(LOG_TAG, "Can't listen to query " + query, databaseError.toException());
        }
    }
}

Answer 1

这是@JobM 帖子的查询版本。谢谢@JobM!为了清楚起见，我建议将@JobM 的版本重命名为 FirebaseDocumentLiveData。

import android.arch.lifecycle.LiveData;
import android.os.Handler;
import android.util.Log;

import com.google.firebase.firestore.EventListener;
import com.google.firebase.firestore.FirebaseFirestoreException;
import com.google.firebase.firestore.ListenerRegistration;
import com.google.firebase.firestore.Query;
import com.google.firebase.firestore.QuerySnapshot;

import javax.annotation.Nullable;

public class FirebaseQueryLiveData extends LiveData<QuerySnapshot> {
    public static final String TAG = "FbaseQueryLiveData";

    private Query query;
    private final MyValueEventListener listener = new MyValueEventListener();
    private ListenerRegistration listenerRegistration;

    private boolean listenerRemovePending = false;
    private final Handler handler = new Handler();

    public FirebaseQueryLiveData(Query query) {
        this.query = query;
    }

    private final Runnable removeListener = new Runnable() {
        @Override
        public void run() {
            listenerRegistration.remove();
            listenerRemovePending = false;
        }
    };

    @Override
    protected void onActive() {
        super.onActive();

        Log.d(TAG, "onActive");
        if (listenerRemovePending) {
            handler.removeCallbacks(removeListener);
        }
        else {
            listenerRegistration = query.addSnapshotListener(listener);
        }
        listenerRemovePending = false;
    }

    @Override
    protected void onInactive() {
        super.onInactive();

        Log.d(TAG, "onInactive: ");
        // Listener removal is schedule on a two second delay
        handler.postDelayed(removeListener, 2000);
        listenerRemovePending = true;
    }

    private class MyValueEventListener implements EventListener<QuerySnapshot> {
        @Override
        public void onEvent(@Nullable QuerySnapshot querySnapshot, @Nullable FirebaseFirestoreException e) {
            if (e != null){
                Log.e(TAG, "Can't listen to query snapshots: " + querySnapshot + ":::" + e.getMessage());
                return;
            }
            setValue(querySnapshot);
        }
    }
}