Question

我有一个类来从我的数据库中读取数据，但它总是返回null。

这是java文件

public class UserActivity extends AppCompatActivity {

    TextView textView;
    private FirebaseDatabase mFirebaseDatabase;
    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private DatabaseReference myRef;
    private String userID;


    private String TAG = "hifiwi";

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


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

        //////////////////////////////////////////////////////////////
        mAuth = FirebaseAuth.getInstance();
        mFirebaseDatabase = FirebaseDatabase.getInstance();
        myRef = mFirebaseDatabase.getReference();
        FirebaseUser user = mAuth.getCurrentUser();
        userID = user.getUid();
        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = mAuth.getCurrentUser();
                if (user != null) {
                    Toast.makeText(UserActivity.this, "Signed in with " + user.getEmail(), Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(UserActivity.this, "Successfully signed out...", Toast.LENGTH_SHORT).show();
                }
            }
        };

        myRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                showData(dataSnapshot);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });


        ///////////////////////////////////////////////////////////////


    }

    private void showData(DataSnapshot dataSnapshot) {
        for (DataSnapshot ds : dataSnapshot.getChildren()) {
            UserInformation uInfo = new UserInformation();
            uInfo.setEmail(ds.child(userID).getValue(UserInformation.class).getEmail());
            uInfo.setName(ds.child(userID).getValue(UserInformation.class).getName());
            uInfo.setPassword(ds.child(userID).getValue(UserInformation.class).getPassword());
            uInfo.setPhoneno(ds.child(userID).getValue(UserInformation.class).getPhoneno());

            Log.i(TAG, " " + uInfo.getEmail());    //Always returning null
            Log.i(TAG, " " + uInfo.getName());    //Always returning null
            Log.i(TAG, " " + uInfo.getPassword());    //Always returning null
            Log.i(TAG, " " + uInfo.getPhoneno());    //Always returning null

        }
    }

    @Override
    protected void onStart() {
        super.onStart();

        mAuth.addAuthStateListener(mAuthListener);
    }

    @Override
    protected void onStop() {
        super.onStop();

        mAuth.removeAuthStateListener(mAuthListener);
    }
}

日志语句始终返回 null 。

这是t2-login下的数据库结构（项目名称）。

{
  "Users" : {
    "8dQ8unnqQXa69nkxUFKrcgiTM3S2" : {
      "emailuser" : "sam@gmail.com",
      "mobileUser" : "1234567899",
      "nameuser" : "sam",
      "passworduser" : "sammypp"
    },
    "DIMBAk4CHZdWGbxN9kPESwIrw9b2" : {
      "emailuser" : "hsjsjsjjsjsj@mdm.mdmdmdmndn",
      "mobileUser" : "9999999999",
      "nameuser" : "hshs",
      "passworduser" : "ppppppl"
    },
    "YJhf16ZyfWUn1Dou3BPcIkSSmVm1" : {
      "emailuser" : "test2@gmail.com",
      "mobileUser" : "1234567892",
      "nameuser" : "test2",
      "passworduser" : "test2pp"
    },
    "yQEFEe5x06hvSZP18Mmb6OfNqnB2" : {
      "emailuser" : "test1@gmail.com",
      "mobileUser" : "1234567891",
      "nameuser" : "test1",
      "passworduser" : "test1pp"
    }
  }
}

UserInformation.class

package com.rishav.t2;

/**
 * Created by rishav on 6/27/2017.
 */

public class UserInformation {
    private String email;
    private String name;
    private String phoneno;
    private String password;

    public UserInformation() {
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhoneno() {
        return phoneno;
    }

    public void setPhoneno(String phoneno) {
        this.phoneno = phoneno;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

Answer 1

试试这种方式

FirebaseDatabase database = FirebaseDatabase.getInstance();
     DatabaseReference myRef = database.getReference("users");
     myRef.addValueEventListener(new ValueEventListener() { 
            @Override 
            public void onDataChange(DataSnapshot dataSnapshot) {
                userList = new ArrayList<User>();
                dataSnapshot.getChildrenCount();
                //List<User> list= new ArrayList<User>(); 
                for (DataSnapshot childDataSnapshot : dataSnapshot.getChildren()) {
                    User user = childDataSnapshot.getValue(User.class);
                    userList.add(user);
                } 
                Log.e("hello","childDataSnapshot"+ userList.size());

                adapter.update(userList); 

            } 

            @Override 
            public void onCancelled(DatabaseError error) {
                // Failed to read value 
                Log.w("MY", "Failed to read value.", error.toException());
            } 
        });

Answer 2

将myRef设置为：myRef = FirebaseDatabase.getInstance().getReference("Users").child(user.getUid());

同样改变这个：

  private void showData(DataSnapshot dataSnapshot) {

            UserInformation uInfo = ds.getValue(UserInformation.class);
            Log.i(TAG, " " + uInfo.getEmail());    //Always returning null
            Log.i(TAG, " " + uInfo.getName());    //Always returning null
            Log.i(TAG, " " + uInfo.getPassword());    //Always returning null
            Log.i(TAG, " " + uInfo.getPhoneno());    //Always returning null


    }

让UserInformation类变量与firebase数据库中存在的键名匹配：

public class UserInformation {
public String emailuser;
public String nameuser;
public String mobileUser;
public String passworduser;

public UserInformation() {
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getPhoneno() {
    return phoneno;
}

public void setPhoneno(String phoneno) {
    this.phoneno = phoneno;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

}

Answer 3

试试这个

  myRef.child("Users").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                showData(dataSnapshot);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

Answer 4

您是否检查了firebase项目设置的规则

Firebase规则提供了一种在执行读写操作时识别用户角色的方法。在执行任何CRUD操作之前，这些规则将在服务器上充当安全层。默认情况下，规则允许用户执行read＆amp; amp;只有在认证后才能写入操作。

The below rules allow authenticated users only to read or write data.
{
  "rules": {
    ".read": "auth != null",
    ".write": "auth != null"
  }
}

以下规则允许每个人阅读＆amp;无需身份验证即可写入数据。

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

您还可以使用这些规则在插入数据库之前验证数据。例如，下面的规则使用电子邮件正则表达式将名称验证为少于50个字符并使电子邮件有效。

{
    "rules": {
        ".read": true,
        ".write": true,
        "users": {
            "$user": {
                "name": {
                    ".validate": "newData.isString() && newData.val().length < 50"
                },
                "email": {
                    ".validate": "newData.isString() && newData.val().matches(/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}$/i)"
                }
            }
        }
    }
}

有关详细教程，请查看此link

每次阅读时，Firebase数据库都会返回null

4 个答案: