Question

目标

通过中的数据树获取当前用户的数据，例如名称，地址，邻居。 Firebase数据库

数据树的图片

Desrciption

数据树中的“伦敦”和“华盛顿”子项由管理员帐户添加，这意味着它们不是固定的，可以添加其他子项，如“纽约”。

这意味着新编辑的数据树将在“用户”下，将有“伦敦”，“华盛顿”和“纽约”

其他孩子，例如下面显示的孩子是固定的。

卫兵
- 名称
- 附近
警
- 地址
- 名称
- 附近
驻地
- 地址
- 图像
- 名称
- 附近
- 位置
- 状态

问题

在尝试提示登录的当前用户的数据后，我收到“java.lang.NullPointerException”。

错误显示在代码String stgUserHomeName = dataSnapshot.child("Users").getValue().toString();上。

我之前能够获得我想要的数据，例如“姓名”，“地址”等等，但是当我在未固定的父母如“伦敦”中添加时遇到问题“和”华盛顿“。

设置活动类

import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;
import com.squareup.picasso.Callback;
import com.squareup.picasso.NetworkPolicy;
import com.squareup.picasso.Picasso;

import java.io.File;


public class SettingsActivity extends AppCompatActivity {

    private DatabaseReference jSettingsDatabase;
    private FirebaseUser jFirebaseCurrentUser;

    private Toolbar jSettingsToolbar;

    private ImageView jSettingsImageView;
    private TextView jSettingsDisplayName;
    private TextView jSettingsStatus;
    private TextView jSettingsAddress;
    private TextView jSettingsHomeName;

    private Button jSettingsDetailsBtn;
    private Button jSettingsImageBtn;

    private static final int jSettingsGallerySelect = 1;

    private StorageReference jSettingsStorageReference;

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

        jSettingsStorageReference = FirebaseStorage.getInstance().getReference();

        jFirebaseCurrentUser = FirebaseAuth.getInstance().getCurrentUser();

        String settingsUserID = jFirebaseCurrentUser.getUid();

        jSettingsDatabase = FirebaseDatabase.getInstance().getReference().child("Resident").child(settingsUserID);
        jSettingsDatabase.keepSynced(true);

        jSettingsImageView = (ImageView) findViewById(R.id.settingUserImg);

        jSettingsToolbar = (Toolbar) findViewById(R.id.settingsToolBar);
        setSupportActionBar(jSettingsToolbar);
        getSupportActionBar().setTitle("Settings");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        jSettingsDisplayName = (TextView) findViewById(R.id.settingUserNameTxt);
        jSettingsStatus = (TextView) findViewById(R.id.settingUserStatusTxt);
        jSettingsAddress = (TextView) findViewById(R.id.settingUserAddressTxt);
        jSettingsHomeName = (TextView) findViewById(R.id.settingsUserHomeTxt);

        jSettingsDetailsBtn = (Button) findViewById(R.id.settingChangeDetailsBtn);
        jSettingsImageBtn = (Button) findViewById(R.id.settingChangeImageBtn);

        jSettingsDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String stgUserHomeName = dataSnapshot.child("Users").getValue().toString();
                String stgUserName = dataSnapshot.child("Users").child(stgUserHomeName).child("name").getValue().toString();
                String stgUserStatus = dataSnapshot.child("Users").child(stgUserHomeName).child("status").getValue().toString();
                String stgUserHomeAddress = dataSnapshot.child("Users").child(stgUserHomeName).child("address").getValue().toString();
                final String stgUserImage = dataSnapshot.child("Users").child(stgUserHomeName).child("image").getValue().toString();

                jSettingsDisplayName.setText(stgUserName);
                jSettingsStatus.setText(stgUserStatus);
                jSettingsAddress.setText(stgUserHomeAddress);

                if(!stgUserImage.equals("default")){
                    Picasso.with(SettingsActivity.this).load(stgUserImage).networkPolicy(NetworkPolicy.OFFLINE)
                            .placeholder(R.drawable.avataricon).into(jSettingsImageView, new Callback() {
                        @Override
                        public void onSuccess() {

                        }

                        @Override
                        public void onError() {
                            Picasso.with(SettingsActivity.this).load(stgUserImage).placeholder(R.drawable.avataricon).into(jSettingsImageView);
                        }
                    });
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        jSettingsDetailsBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String stgUserStatusValue = jSettingsStatus.getText().toString();
                String stgUserAddressValue = jSettingsAddress.getText().toString();
                String stgUserNameValue = jSettingsDisplayName.getText().toString();
                Intent intentDetails = new Intent(SettingsActivity.this, DetailsActivity.class);
                intentDetails.putExtra("stgUserNameValue" , stgUserNameValue);
                intentDetails.putExtra("stgUserStatusValue", stgUserStatusValue);
                intentDetails.putExtra("stgUserAddressValue", stgUserAddressValue);
                startActivity(intentDetails);
            }
        });

        jSettingsImageBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intentGallery = new Intent();
                intentGallery.setType("image/*");
                intentGallery.setAction(Intent.ACTION_GET_CONTENT);
                startActivityForResult(Intent.createChooser(intentGallery, "SELECT IMAGE"), jSettingsGallerySelect);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(requestCode == jSettingsGallerySelect && resultCode == RESULT_OK){

            Uri imageUri = data.getData();

            String currentUserID = jFirebaseCurrentUser.getUid();

            StorageReference imageFilePath = jSettingsStorageReference.child("profileImages").child(currentUserID+".jpg");

            imageFilePath.putFile(imageUri).addOnCompleteListener(new OnCompleteListener<UploadTask.TaskSnapshot>(){
                @Override
                public void onComplete(@NonNull Task<UploadTask.TaskSnapshot> task) {
                    @SuppressWarnings("VisibleForTests")
                    String downloadImageUrl = task.getResult().getDownloadUrl().toString();

                    jSettingsDatabase.child("image").setValue(downloadImageUrl).addOnCompleteListener(new OnCompleteListener<Void>() {
                        @Override
                        public void onComplete(@NonNull Task<Void> task) {
                            if(task.isSuccessful()){
                                Toast.makeText(SettingsActivity.this, "Upload Successful", Toast.LENGTH_SHORT).show();
                            }else{
                                Toast.makeText(SettingsActivity.this, "Upload Failed", Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
                }
            });
        }
    }
}

代码说明

jSettingsHomeName和stgUserHomeName应该是“伦敦”，“华盛顿”等。

解决几乎相似的问题

在链接：How to get child of child value from firebase in android?中，它显示了程序员如何获得孩子的孩子但是我无法遵循的原因是因为我的“伦敦”和“华盛顿”子级< strong>未修复

更新：试用Ewald B提供的解决方案。

jSettingsDatabase.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot node : dataSnapshot.getChildren()) {
            String stgUserHomeName = node.getKey();
            String stgUserName = node.child("Resident").child(settingsUserID).child("name").getValue().toString();
            String stgUserStatus = node.child("Resident").child(settingsUserID).child("status").getValue().toString();
            String stgUserHomeAddress = node.child("Resident").child(settingsUserID).child("address").getValue().toString();
            final String stgUserImage = node.child("Resident").child(settingsUserID).child("image").getValue().toString();

            jSettingsHomeName.setText(stgUserHomeName);
            jSettingsDisplayName.setText(stgUserName);
            jSettingsStatus.setText(stgUserStatus);
            jSettingsAddress.setText(stgUserHomeAddress);

            if(!stgUserImage.equals("default")){
                Picasso.with(SettingsActivity.this).load(stgUserImage).networkPolicy(NetworkPolicy.OFFLINE)
                        .placeholder(R.drawable.avataricon).into(jSettingsImageView, new Callback() {
                    @Override
                    public void onSuccess() {

                    }

                    @Override
                    public void onError() {
                        Picasso.with(SettingsActivity.this).load(stgUserImage).placeholder(R.drawable.avataricon).into(jSettingsImageView);
                    }
                });
            }
        }

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

错误

com.example.task.app.SettingsActivity $ 1.onDataChange（SettingsActivity.java:91）中的java.lang.NullPointerException

第91行指向String stgUserName = node.child("Resident").child(settingsUserID).child("name").getValue().toString();

Answer 1

仅用于测试目的将Firebase实时数据库规则设置为允许任何人读写

例如

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

查看Firebase规则文档 https://firebase.google.com/docs/database/security/

Answer 2

根据数据模型并查看此声明

jSettingsDatabase = FirebaseDatabase.getInstance().getReference().child("Resident").child(settingsUserID);

User下面没有节点/Resident/userId。查询需要从数据库的根开始，我认为它是User。

为了获得London, Washington, etc.，您需要调整代码：

jSettingsDatabase = FirebaseDatabase.getInstance().getReference().child("Users");
...
jSettingsDatabase.addValueEventListener(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {
      for(DataSnapshot node : dataSnapshot.getChildren()) {
         // you will get all cities
         String stgUserHomeName = node.getKey();
         if(!"Washington".equals(stgUserHomeName)) // or whatever city you need
            continue;
         // add some more conditional logic to cope with the distinct subtrees that don't have the same properties
         // London's Resident has more properties than Washington --> exception is thrown then
         // to get the resident's data
         node.child("Resident").child(userId).child("address")...
         node.child("Resident").child(userId).child("image")...
         // or
         node.child("Resident").child(userId).getValue(Resident.class);
         ...
      }
      ....
   }
});

此查询所需的树中没有用户ID。但根据数据库的访问规则，可能需要它。显然，其他查询也需要进行调整。城市名称也不是值，而是键（必须是唯一的），因此调用DataSnapshot.getKey()方法非常重要。

在您的情况下，将提取用户向下的整个数据库，并且在客户端上将丢弃所有不需要的城市。这是浪费资源。

Answer 3

只要节点上有多个子节点，就需要在循环中扫描它们。该事件表明＆＃34;一些＆＃34;孩子被改变了。此外，尝试将事件更改为onChildAdded。如下所示：

public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        if (dataSnapshot.getChildrenCount() > 0) {
            for (DataSnapshot ds1 : dataSnapshot.getChildren()) {
                String stgUserHomeName = ds1.getValue.toString(); 
                 .....

Android - Firebase - 获取子数据的子项

3 个答案: