Android架构组件与Firebase特别是Firestore

Question

我正在浏览Doug Stevenson（Firebase开发者倡导者）的博客，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。

有一个类Firebase QueryLiveData，它形成了一个可重用的类来管理所有Firebase查询以及实现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fiRecovery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

献给Kotlin的恋人：）

import android.os.Handler
import androidx.annotation.Nullable
import androidx.lifecycle.LiveData
import com.google.firebase.firestore.*
import timber.log.Timber

class FirebaseQueryLiveData(private val query: Query) : LiveData<QuerySnapshot>() {
    private val listener = MyValueEventListener()
    private var listenerRegistration: ListenerRegistration? = null

    private var listenerRemovePending = false
    private val handler = Handler()

    private val removeListener = Runnable {
        listenerRegistration!!.remove()
        listenerRemovePending = false
    }

    override fun onActive() {
        super.onActive()

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

    override fun onInactive() {
        super.onInactive()

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

    private inner class MyValueEventListener : EventListener<QuerySnapshot> {
        override fun onEvent(@Nullable querySnapshot: QuerySnapshot?, @Nullable e: FirebaseFirestoreException?) {
            if (e != null) {
                Timber.e(e, "Can't listen to query snapshots: %s", querySnapshot)
                return
            }
            value = querySnapshot
        }
    }
}

Answer 2

这是@JobM post的查询版本。谢谢@JobM！为了清晰起见，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);
        }
    }
}