数据快照没有获取数据吗？

Question

driverLocationRef.child(driverFoundID).child("l").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        if (snapshot.exists()) {
            List<Object> driverLocationMap = (List<Object>) snapshot.getValue();
            double LocationLat = 0;
            double LocationLng = 0;

            vanfind.setText("Driver Found");

            if (driverLocationMap.get(0) != null) {
                LocationLat = Double.parseDouble(driverLocationMap.get(0).toString());

            }
            if (driverLocationMap.get(1) != null) {
                LocationLng = Double.parseDouble(driverLocationMap.get(1).toString());

            }

            LatLng DriverLatLng = new LatLng(LocationLat, LocationLng);
            if (DriverMarker != null) {
                DriverMarker.remove();
            }

            Location location1 = new Location("");
            location1.setLatitude(latLng.latitude);
            location1.setLongitude(latLng.longitude);

            Location location2 = new Location("");
            location2.setLatitude(DriverLatLng.latitude);
            location2.setLongitude(DriverLatLng.longitude);

            float Distance = location1.distanceTo(location2);
            vanfind.setText("Driver Found:" + String.valueOf(Distance));

            DriverMarker = googleMap.addMarker(new MarkerOptions().position(DriverLatLng).title("your Driver is here"));


        }
    }


    @Override
    public void onCancelled(@NonNull DatabaseError error) {

    }
});

在driverLocationRef.child(driverFoundID).child("l")行之后，不执行任何代码。我在调试器控制台中检查它，但它不工作后，下面的第一行代码没有执行。

它的Uber或类似于Cream的应用。一切都很好，但是这个数据截图并没有让数据无法工作。

Answer 1

我认为你应该这样写：

final DatabaseReference
driverLocationRef = Firebasedatabase.getInstance().getReference().child(driverFoundID).child("l");

然后，您可以继续编写

driverLocationRef.addOnCompleteListener...

Answer 2

我认为你应该使用接口来获取LocationLat和LocationLng。然后在onCallBack中完成所有工作。像这样声明一个接口：

public interface MyCallback{
    void onCallback(double LocationLat,double LocationLng);
}

然后将侦听器包装在一个函数中

public void getData(final MyCallback myCallback){
    driverLocationRef.child(driverFoundID).child("l").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            if (snapshot.exists()) {
                List<Object> driverLocationMap = (List<Object>) snapshot.getValue();
                double LocationLat = 0;
                double LocationLng = 0;

                vanfind.setText("Driver Found");

                if (driverLocationMap.get(0) != null) {
                    LocationLat = Double.parseDouble(driverLocationMap.get(0).toString());

                }
                if (driverLocationMap.get(1) != null) {
                    LocationLng = Double.parseDouble(driverLocationMap.get(1).toString());
                }
                myCallback.onCallback(LocationLat,LocationLng);
            }
        }
        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });
}

然后在你需要的时候像这样调用函数：

getData(new MyCallback() {
        @Override
        public void onCallback(double LocationLat, double LocationLng) {
            LatLng DriverLatLng = new LatLng(LocationLat, LocationLng);
            if (DriverMarker != null) {
                DriverMarker.remove();
            }

            Location location1 = new Location("");
            location1.setLatitude(latLng.latitude);
            location1.setLongitude(latLng.longitude);

            Location location2 = new Location("");
            location2.setLatitude(DriverLatLng.latitude);
            location2.setLongitude(DriverLatLng.longitude);

            float Distance = location1.distanceTo(location2);
            vanfind.setText("Driver Found:" + String.valueOf(Distance));

            DriverMarker = googleMap.addMarker(new MarkerOptions().position(DriverLatLng).title("your Driver is here"));
        }
    });

希望这能行得通。