Question

当我启动此活动时，我的应用程序停止。我需要从数据库获取坐标并放置标记。我不知道问题在哪里。

我的数据库：

<script src="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.100.2/js/materialize.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.100.2/css/materialize.min.css" rel="stylesheet"/>
<body>
    <div id="homeBody">

        <div class="row">
            <div class="col s12 m12 no-padding">
                <div class="card">
                    <div class="card-content white-text center-align scm-primary scm-card-content">
                        Europe - Champions League
                    </div>
                    <div class="card-action no-padding">
                        
                        <!-- Partidas -->
                        <div class="row no-padding">
                            <div class="col s12 m12">
                                <div class="card scm-match-card">
                                    <div class="card-content scm-card-content">
                                        <div class="row no-padding">
                                            <div class="col s8 small-text scm-primary-text">Paris Saint Germain X Atlético de Madrid</div>
                                            <div class="col s4 right small-text right-align scm-primary-text">30/12 - 15:00</div>
                                        </div>
                                    </div>
                                    <div class="card-action center-align scm-card-content">
                                        
                                        <div class="row">
                                            <div class="col s3 m3 l4">
                                                <a class="scm-odd-button">
                                                    <span>
                                                        <strong>2,00</strong>
                                                        <br>
                                                        <small>Home</small>
                                                    </span>
                                                </a>
                                            </div>
    
                                            <div class="col s3 m3 l4">
                                                <a class="scm-odd-button">
                                                    <span>
                                                        <strong>2,00</strong>
                                                        <br>
                                                        <small>Away</small>
                                                    </span>
                                                </a>
                                            </div>
    
                                            <div class="col s3 m3 l4">
                                                <a class="scm-odd-button">
                                                    <span>
                                                        <strong>2,00</strong>
                                                        <br>
                                                        <small>Paris Saint Germain/Atlético de Madrid</small>
                                                    </span>
                                                </a>
                                            </div>

                                            <div class="col s3 m3 l4">
                                                <a class="scm-odd-button">
                                                    <span>
                                                        <strong>+</strong>
                                                        <br>
                                                        <small>More</small>
                                                    </span>
                                                </a>
                                            </div>
                                        </div>

                                    </div>
                                </div>
                            </div>
                        </div>

                    </div>
                </div>
            </div>
        </div>

    </div>
</body>

Answer 1

尝试这样来检索lat和lng

NULL

Answer 2

首先，如果您想要获取所有博客的孩子，那么您应该将您的参考文献放在DatabaseReference f_database = FirebaseDatabase.getInstance().getReference("Blog");

上

将firebase引用放在DatabaseReference f_database = FirebaseDatabase.getInstance().getReference()上时。这将获取数据库的所有节点，例如博客和用户。如果您需要博客信息，则无需获取用户数据。对于 firebase ，这是一个非常糟糕的代码实践。

其次，正如@Benjith binja建议您可以获取所有博客的孩子来获取纬度＆amp;经度。或者，您应该创建一个Blog对象并获取数据。这是一个很好的做法。 https://firebase.google.com/docs/database/android/read-and-write

博客对象：

class Blog {
    public String desc,id,image,time,title,uid,username;
    public Double lat,lng;

    public Blog(String desc, String id, String image, String time, String title, String uid, String username, Double lat, Double lng) {
        this.desc = desc;
        this.id = id;
        this.image = image;
        this.time = time;
        this.title = title;
        this.uid = uid;
        this.username = username;
        this.lat = lat;
        this.lng = lng;
    }
}

firebase监听器看起来像这样：

DatabaseReference f_database = FirebaseDatabase.getInstance().getReference("Blog");
ValueEventListener listener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if(dataSnapshot.exists()){
            for(DataSnapshot snapshot:dataSnapshot.getChildren()){
                // Get Blog object and use the values to update the UI
                Blog blog = snapshot.getValue(Blog.class);
                LatLng location = new LatLng(blog.lat,blog.lng);
                googleMap.addMarker(new MarkerOptions().position(location).title("pedik"));
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
};
f_database.addListenerForSingleValueEvent(listener);

由于Map的使用错误，必须发生错误。以下是代码的外观。

@Override
public void onMapReady(GoogleMap googleMap) {

mMap = googleMap;
f_database.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot child : dataSnapshot.getChildren()) {
            Map data = (Map) child.getValue();
            Map mCoordinate = (HashMap)data.get("Blog");
            //mCoordinate is a map with values of all the children of Blog
            for(String key: mCoordinate.keySet()){
                Map mCoordinateChildMap = (HashMap) mCoordinate.get(key)
                double latitude = (double) (mCoordinateChildMap.get("lat"));
                double longitude = (double) (mCoordinateChildMap.get("lng"));
                LatLng location = new LatLng(latitude,longitude);
                googleMap.addMarker(new MarkerOptions().position(location).title("pedik"));   
            }
        }
    }


    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

我无法从firebase获得标记

2 个答案: