如何訪問（修改、添加元素）到 Java 內部類中的 ArrayList/Collection？

Question

我有這個搜索功能，可以使用 GeoFire 使用 firebase 數據庫搜索特定用戶。

我想做的事 ：

在GeoQueryEventListener() & onKeyEntered ，我想將找到的每個鍵添加到 ArrayList （在onKeyEntered()之外）。

我遇到的問題：

當我在onKeyEntered()打印它時，它可以工作。 但是一旦我退出GeoQueryEventListener() ， keysGeolocated就為空

public ArrayList<User> search(GeoFire geoFire, int day, final boolean isBartender, double latitude, double longitude, double radius, double rate, double nightlyRate, double hourlyRate, final String speciality){

    keysGeolocated = new ArrayList<>();
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    root = database.getReference();
    DatabaseReference usersRef = root.child("Users");

    GeoQuery geoQuery = geoFire.queryAtLocation(new GeoLocation(latitude, longitude), radius);
    geoQuery.addGeoQueryEventListener(new MyGeoListener(keysGeolocated));

    System.out.println("KEYS GEOLOCATED" + keysGeolocated);

    final ArrayList<User> result = new ArrayList<>();

    for(String key : keysGeolocated){

        Query queryByLocation = usersRef.orderByKey().equalTo(key);
        DatabaseReference refToLocationQuery = queryByLocation.getRef();

        if(checkRefNull(refToLocationQuery) == true) {
            System.out.println("QUERY BY LOCATION NULL");
            continue;
        }

        Query queryByTypeOfUser  = refToLocationQuery.orderByChild("isBarTender").equalTo(isBartender);
        DatabaseReference refToTypeOfUserQuery = queryByTypeOfUser.getRef();

        if(checkRefNull(refToTypeOfUserQuery) == true) {
            System.out.println("QUERY BY TYPE NULL");
            continue;
        }
        Query queryByRate  = refToTypeOfUserQuery.orderByChild("rate").startAt(rate);
        DatabaseReference refToRateQuery = queryByRate.getRef();

        if(checkRefNull(refToRateQuery) == true) {
            System.out.println("QUERY BY RATE NULL");
            continue;
        }

        DatabaseReference finalRef = null;

        if(isBartender == true){

            if(nightlyRate == 0){
                Query queryByPrice  = refToRateQuery.orderByChild("nightlyRate").endAt(nightlyRate);
                finalRef = queryByPrice.getRef();
            }
            else if(hourlyRate == 0){
                Query queryByPrice  = refToRateQuery.orderByChild("hourlyRate").endAt(hourlyRate);
                finalRef = queryByPrice.getRef();
            }

            //TODO Impelement checks for available dates

        }
        else{
            finalRef = refToRateQuery;
        }

        finalRef.addValueEventListener(new ValueEventListener() {

            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                if(dataSnapshot.getValue()!=null){

                    User userFound = dataSnapshot.getValue(User.class);

                    if(isBartender == true){
                        Bartender barTenderFound = (Bartender) userFound;
                        if(speciality != null){
                            if(barTenderFound.getSpeciality().contains(speciality)){
                                result.add(barTenderFound);
                            }
                        }
                        else{
                            result.add(barTenderFound);
                        }
                    }
                    else{
                        result.add(userFound);
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

    return result;
}

public boolean checkRefNull(DatabaseReference ref){

    final boolean[] result = new boolean[1];
    result[0] = false;

        ref.addValueEventListener(new ValueEventListener() {


            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                System.out.println("TEST1");
                if(dataSnapshot.getValue()==null){
                    result[0] = true;
                    System.out.println("TESTTEST");
                }
                else{
                    System.out.println("TESTTEST TRUE" + dataSnapshot.getValue());
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
    });

    return result[0];
}

public void setBarTender(boolean barTender){

    this.barTender = barTender;
}
}

class MyGeoListener implements GeoQueryEventListener {

private ArrayList<String> keysGeolocated;

MyGeoListener(ArrayList<String> keysGeolocated){
    this.keysGeolocated = keysGeolocated;
}

@Override
public void onKeyEntered(String key, GeoLocation location) {
    keysGeolocated.add(key);
}

@Override
public void onKeyExited(String key) {

}

@Override
public void onKeyMoved(String key, GeoLocation location) {

}

@Override
public void onGeoQueryReady() {

}

@Override
public void onGeoQueryError(DatabaseError error) {

}
}

Answer 1

創建一個擴展該偵聽器並覆蓋所有方法的類

class MyGeoListener extends GeoQueryEventListener{

    private ArrayList<String> keysGeolocated;

    MyGeoListener(ArrayList<String> keysGeolocated){
          this.keysGeolocated = keysGeolocated;
    }

    @Override
    public void onKeyEntered(String key, GeoLocation location) {
        keysGeolocated.add(key);
        System.out.println("1111111111 : "+keysGeolocated);
        System.out.println("2222222222 : "+key);
    }

    @Override
    public void onKeyExited(String key) {

    }

    @Override
    public void onKeyMoved(String key, GeoLocation location) {

    }

    @Override
    public void onGeoQueryReady() {

    }

    @Override
    public void onGeoQueryError(DatabaseError error) {

    }
}

現在使用這個類如下：

geoQuery.addGeoQueryEventListener(new MyGeoListener(keysGeolocated));

由於偵聽器是異步的並且需要時間來填充列表，因此立即下一次調用將始終在列表中不打印任何值。

嘗試將打印內容放入延遲時間為 30000 毫秒的延遲處理程序中。 您可能會在列表中看到條目，因為那時監聽器事件應該已經觸發。

由於 arraylist 是可變的，並且您正在傳遞它的引用，因此當偵聽器調用時，參數中的 arraylist 也將被修改。

祝你好運，如果你還有問題，請告訴我。