这是我的数据:

{
  "users" : {
    "00c49c66-7ac8-9a48-7c4541d8bac6" : {
      "email" : "d@gmail.com",
      "gender" : "m",
      "name" : "deepak",
      "user_id" : "00c49c66-7ac8-9a48-7c4541d8bac6"
    },
    "1cb9c1de-1fcf-a2cc-bf78c84e03c8" : {
      "email" : "e@gmail.com",
      "gender" : "f",
      "name" : "ekta",
      "user_id" : "1cb9c1de-1fcf-a2cc-bf78c84e03c8"
    },
    "38211c3f-6c48-8987-0c698b9b9b52" : {
      "email" : "c@gmail.com",
      "gender" : "m",
      "name" : "chirag",
      "user_id" : "38211c3f-6c48-8987-0c698b9b9b52"
    },
    "a536cf1f-419f-9658-cfb5f5a8ec78" : {
      "email" : "a@gmail.com",
      "gender" : "m",
      "name" : "aniket",
      "user_id" : "a536cf1f-419f-9658-cfb5f5a8ec78"
    },
    "c80d828d-48d7-a79a-9cc558cd1960" : {
      "email" : "b@gmail.com",
      "gender" : "f",
      "name" : "bhakti",
      "user_id" : "c80d828d-48d7-a79a-9cc558cd1960"
    }
  }
}


现在我要获取“性别”为“ m”的“名称”和“ id”

请任何人告诉我如何从Android客户端向Firebase触发这样的查询。

我尝试了firebase和其他一些链接提供的教程,但没有通过。

大多数解决方案都在Javascript中,而Firebase的Java API中则需要Android。

我试过了

public class ActivityHome extends Activity {
    String strLoggedInUserID;
    TextView tvData;
    Firebase fbRef = new Firebase("https://myurl.com/users");


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);

        tvData = (TextView) findViewById(R.id.tvData);

        Query queryRef = fbRef.orderByChild("gender").equalTo("m");

        Bundle extras = getIntent().getExtras();
        strLoggedInUserID = extras.getString("userID");

        fbRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });

        queryRef.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {

                //long longChildCount = dataSnapshot.getChildrenCount();

                // tvData.setText(dataSnapshot).toString();
                tvData.setText(s);

            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {

            //tvData.setText(s);

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {

            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });

    }
}

最佳答案

您的查询代码看起来正确,但是您不打印用户。

由于您要添加ChildEventListener,因此将为每个孩子调用它:

queryRef.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {

        //long longChildCount = dataSnapshot.getChildrenCount();

        // tvData.setText(dataSnapshot).toString();
        tvData.setText(s);

    }


dataSnapshot参数包含有关单个用户的信息。要打印其密钥,名称和电子邮件:

queryRef.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        System.out.println(dataSnapshot.key());
        System.out.println(dataSnapshot.child("name").getValue());
        System.out.println(dataSnapshot.child("email").getValue());
    }


或者,您可以使用ValueEventListener一次收听所有孩子。

private static class User {
    String email;
    String gender;
    String name;
    @JsonProperty("user_id")
    String userId;

    public String getEmail() { return email; }
    public String getGender() { return gender; }
    public String getName() { return name; }
    public String getUserId() { return userId; }
}
queryRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot child: dataSnapshot.getChildren()) {
            User user = child.getValue(User.class);
            System.out.println(user.getEmail());
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {
    }
});


在最后一个代码片段中,我还使用一个User类从DataSnapshot获取数据。随着应用程序的增长,这比不断调用DataSnapshot.child()更方便。

section on reading data in the Firebase documentation中对此进行了介绍。

10-05 21:17
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