java - 我的 onChildAdded() 在使用 Firebase Push() 时有效，但在更新时无效

Question

每当我使用 updateChildren() 方法时，我的 onChildAdded() 方法似乎都不起作用。它与 push().setValue() 方法配合使用。这两种方法都可以将数据发送到 Firebase。有什么想法吗？

谢谢!

这是 push() 方法(有效)

private void saveToFirebase() {

    String username = getIntent().getStringExtra("Username");

    //takes string user input and creates a child of Gaben(parent)
    Firebase usersRef = myFirebaseRef.child(username);

    //sub child
    Firebase location = usersRef.child("details");

    Map mLocations = new HashMap();
    mLocations.put("timestamp", mLastUpdateTime);
    Map mCoordinate = new HashMap();

    myFirebaseRef.push().setValue(mLocations);
}

private void drawLocations() {
    // Get only latest logged locations - since 'START' button clicked
    Query queryRef = myFirebaseRef.orderByChild("timestamp").startAt(startLoggingTime);
    // Add listener for a child added at the data at this location
    queryRef.addChildEventListener(new ChildEventListener() {
        LatLngBounds bounds;
        LatLngBounds.Builder builder = new LatLngBounds.Builder();

        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            Map data = (Map) dataSnapshot.getValue();
            String timestamp = (String) data.get("timestamp");
            // Get recorded latitude and longitude
            Map mCoordinate = (HashMap) data.get("location");

            double latitude = (double) (mCoordinate.get("latitude"));
            double longitude = (double) (mCoordinate.get("longitude"));

            // Create LatLng for each locations
            LatLng mLatlng = new LatLng(latitude, longitude);

            // Make sure the map boundary contains the location
            builder.include(mLatlng);
            bounds = builder.build();

            //get username input from login activity
            String username = getIntent().getStringExtra("Username");

            MarkerOptions mMarkerOption = new MarkerOptions()
                    // Add a marker for each logged location
                    .position(mLatlng)
                    .title(username)
                    .snippet(timestamp)
                    .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE));

            Marker nMarker = mMap.addMarker(mMarkerOption);
            nMarker.showInfoWindow();

            // Zoom map to the boundary that contains every logged location
            mMap.animateCamera(CameraUpdateFactory.newLatLngBounds(bounds, MAP_ZOOM_LEVEL));
        }
    });
}

这里的update()方法不起作用

private void saveToFirebase() {
    String username = getIntent().getStringExtra("Username");

    //takes string user input and creates a child of Gaben(parent)
    Firebase usersRef = myFirebaseRef.child(username);

    //sub child
    Firebase location = usersRef.child("details");

    Map mLocations = new HashMap();
    mLocations.put("timestamp", mLastUpdateTime);
    Map  mCoordinate = new HashMap();

    mCoordinate.put("latitude", mCurrentLocation.getLatitude());
    mCoordinate.put("longitude", mCurrentLocation.getLongitude());

    //updates location in firebase
    location.updateChildren(mLocations);
    location.updateChildren(mCoordinate);
}

基本上，唯一的区别是推送方法每次都会创建唯一的 ID，而另一种方法只是更新它。

唯一的区别是这些行

    location.updateChildren(mCoordinate);

还有这个

    myFirebaseRef.push().setValue(mLocations);

Answer 1

更新现有位置与添加新位置不同。

来自Firebase documentation on event types :

The onChildAdded event ... is triggered once for each existing child and then again every time a new child is added to the specified path.

还有:

The onChildChanged event is triggered any time a child node is modified.

由于您要添加新位置并修改现有位置，因此必须同时实现 onChildAdded() 和 onChildChanged()。