[英]Issues retrieving data on Android with Firebase
我刚刚学习如何在Android中设置Firebase数据。 我能够写入数据库,但我无法读取它并将其显示在我的应用程序上。 我的应用程序非常简单(它现在只有一个主屏幕)我并不关心数据如何在我正在学习的页面上显示 - 我现在正试图在文本视图中显示它。
这是我的主要活动java:
package com.example.ispotrachel.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import com.firebase.client.DataSnapshot;
import com.firebase.client.Firebase;
import com.firebase.client.FirebaseError;
import com.firebase.client.ValueEventListener;
import java.util.HashMap;
import java.util.Map;
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Firebase.setAndroidContext(this);
Firebase ref = new Firebase("https://blistering-torch-9015.firebaseio.com");
class User {
private int birthYear;
private String fullName;
public User() {
}
public User(String fullName, int birthYear) {
this.fullName = fullName;
this.birthYear = birthYear;
}
public long getBirthYear() {
return birthYear;
}
public String getFullName() {
return fullName;
}
}
User user1 = new User("Name 1", 1982);
User user2 = new User("Name 2", 1972);
Firebase usersRef = ref.child("users");
Map<String, User> users = new HashMap<String, User>();
users.put("user1", user1);
users.put("user 2", user2);
usersRef.setValue(users);
Firebase postRef = ref.child("posts");
Map<String, String> post1 = new HashMap<String, String>();
post1.put("author", "user1");
post1.put("title", "Announcing COBOL, a New Programming Language");
postRef.push().setValue(post1);
Map<String, String> post2 = new HashMap<String, String>();
post2.put("author", "user2");
post2.put("title", "The Turing Machine");
postRef.push().setValue(post2);
ref.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot arg0) {
//System.out.println(arg0.getValue());
TextView textViewSample = (TextView) findViewById(R.id.sampleTextView);
textViewSample.setText(arg0.getValue(String.class));
}
@Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println("the read failed");
}
});
}}
这是我的activity_main.xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<TextView
android:id="@+id/sampleTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world"/>
</LinearLayout>
当我运行应用程序时,它崩溃了。 这是logcat错误消息:
12-27 12:15:02.678 1895-1895/com.example.ispotrachel.myapplication I/art﹕ Not late enabling -Xcheck:jni (already on)
12-27 12:15:02.946 1895-1907/com.example.ispotrachel.myapplication I/art﹕ Background sticky concurrent mark sweep GC freed 3867(286KB) AllocSpace objects, 0(0B) LOS objects, 11% free, 1009KB/1135KB, paused 2.595ms total 117.910ms
12-27 12:15:03.317 1895-1926/com.example.ispotrachel.myapplication D/OpenGLRenderer﹕ Render dirty regions requested: true
12-27 12:15:03.320 1895-1895/com.example.ispotrachel.myapplication D/﹕ HostConnection::get() New Host Connection established 0xa6667e80, tid 1895
12-27 12:15:03.327 1895-1895/com.example.ispotrachel.myapplication D/Atlas﹕ Validating map...
12-27 12:15:03.391 1895-1926/com.example.ispotrachel.myapplication D/﹕ HostConnection::get() New Host Connection established 0xa66ef3b0, tid 1926
12-27 12:15:03.405 1895-1926/com.example.ispotrachel.myapplication I/OpenGLRenderer﹕ Initialized EGL, version 1.4
12-27 12:15:03.422 1895-1926/com.example.ispotrachel.myapplication D/OpenGLRenderer﹕ Enabling debug mode 0
12-27 12:15:03.439 1895-1926/com.example.ispotrachel.myapplication W/EGL_emulation﹕ eglSurfaceAttrib not implemented
12-27 12:15:03.439 1895-1926/com.example.ispotrachel.myapplication W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0xa66b7880, error=EGL_SUCCESS
12-27 12:15:07.474 1895-1926/com.example.ispotrachel.myapplication W/EGL_emulation﹕ eglSurfaceAttrib not implemented
12-27 12:15:07.474 1895-1926/com.example.ispotrachel.myapplication W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0xa66b7880, error=EGL_SUCCESS
12-27 12:15:13.993 1895-1895/com.example.ispotrachel.myapplication D/AndroidRuntime﹕ Shutting down VM
--------- beginning of crash
12-27 12:15:13.993 1895-1895/com.example.ispotrachel.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.ispotrachel.myapplication, PID: 1895 com.firebase.client.FirebaseException: Failed to bounce to type
at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:196)
at com.example.ispotrachel.myapplication.MainActivity$1.onDataChange(MainActivity.java:79)
at com.firebase.client.core.ValueEventRegistration$1.run(ValueEventRegistration.java:48)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token
at [Source: java.io.StringReader@c8f7297; line: 1, column: 1]
at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:575)
at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:46)
at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2034)
at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:192)
at com.example.ispotrachel.myapplication.MainActivity$1.onDataChange(MainActivity.java:79)
at com.firebase.client.core.ValueEventRegistration$1.run(ValueEventRegistration.java:48)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)device not found
TL;博士
看起来您正在尝试将JSON对象加载到String中。
错误消息Failed to bounce to type
表示Firebase客户端收回了一些数据,但无法将其转换为您指定的类型。
有关问题的详细信息
您将在ValueEventListener
向Firebase的根目录添加ValueEventListener
:
ref.addValueEventListener(new ValueEventListener() { ...
在该值事件监听器中,您告诉Firebase将整个Firebase加载为String
:
textViewSample.setText(arg0.getValue(String.class));
如果你有一个非常简单的Firebase只包含一个字符串,这将工作正常。 但是,根据您的其余代码,看起来您的Firebase中有多个String
:)
如何解决它你有几个选择:
将事件监听器附加到树的下方。 您可以将用户的全名作为字符串:
ref.child("users/user1/fullName").addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot arg0) { TextView textViewSample = (TextView) findViewById(R.id.sampleTextView); textViewSample.setText(arg0.getValue(String.class)); } ... }
或者,您可以获得整个用户,但将其解析为User
而不是String
:
ref.child("users/user1/fullName").addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot arg0) { User tempUser = arg0.getValue(User.class); TextView textViewSample = (TextView) findViewById(R.id.sampleTextView); textViewSample.setText(tempUser.getFullName()); } ... }
我有类似的问题。
这是我从firebase检索数据的代码:
DatabaseReference chatRef = database.getReference("chats");
chatRef.keepSynced(true);
Query queryRef = chatRef.orderByChild("id");
queryRef.addChildEventListener(new ChildEventListener() {
// Retrieve new posts as they are added to the database
@Override
public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
ChatPost newPost = snapshot.getValue(ChatPost.class);
ChatPost topic = new ChatPost(newPost.id, newPost.topic);
addChatTopic(topic);
System.out.println("NEW Child Topic: " + newPost.topic);
chatAdapter.addItem(newPost);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
ChatPost newPost = dataSnapshot.getValue(ChatPost.class);
ChatPost topic = new ChatPost(newPost.id, newPost.topic);
addChatTopic(topic);
System.out.println("CHANGED Child Topic: " + newPost.topic);
chatAdapter.updateItem(newPost);
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
ChatPost newPost = dataSnapshot.getValue(ChatPost.class);
ChatPost topic = new ChatPost(newPost.id, newPost.topic);
chatTopicsList.add(topic);
System.out.println("REMOVED Child Topic: " + newPost.topic);
chatAdapter.removeItem(newPost);
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
它一直工作,直到我没有使用push()添加新项目。 我在火力控制台数据看起来像在这里 。
例外文本:
07-05 16:45:07.097 29997-29997 / com.skl.bingofire E / AndroidRuntime:FATAL EXCEPTION:main进程:com.skl.bingofire,PID:29997 com.google.firebase.database.DatabaseException:预期列表时反序列化,但在com.google.android.gms.internal.zzaix.zza(未知来源)的com.google.android.gms.internal.zzaix.zza(未知来源)获得了一个java.util.HashMap类。 go.com.android.gms.internal.zzaix.zzb(未知来源)位于com.google.android.gms.internal.zzaix $ zza的com.google.android.gms.internal.zzaix $ zza.zze(未知来源)。来自com.google.android.gms上的com.google.android.gms.internal.zzaix.zzd(未知来源)的zzaC(未知来源),位于com.google.android.gms的com.google.android.gms.internal.zzaix.zzb(未知来源)。 com.google上的com.google.fireix.database.DataSnapshot.getValue(未知来源)中的com.google.zza.ad.Adain来源(www.inChildAdded(MainActivity.java:228))中的internal.zzaix.zza(未知来源)。 com.google.android.gms.internal.zzagp.z上的android.gms.internal.zzaer.zza(未知来源) zSu(未知来源)位于android.os.Handler.dispatchMessage(处理程序。)的android.os.Handler.handleCallback(Handler.java:739)的com.google.android.gms.internal.zzags $ 1.run(未知来源)。 java:95)在android.app.Looper.loop(Looper.java:148)的android.app.ActivityThread.main(ActivityThread.java:5417)at java.lang.reflect.Method.invoke(Native Method)at com .android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:726)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)07-05 16:45:16.924 29997-30029 / com.skl.bingofire E / DynamiteModule:无法加载模块描述符类:未在路径上找到类“com.google.android.gms.dynamite.descriptors.com.google.firebase.auth.ModuleDescriptor”:DexPathList [[ zip文件“/data/app/com.skl.bingofire-1/base.apk"],nativeLibraryDirectories=[/data/app/com.skl.bingofire-1/lib/arm,/ vendor / lib,/ system / LIB]
我用过这个型号:
class ChatPost {
public String id;
public String topic;
public String color;
public ArrayList<Message> messages;
}
我想通了,我发现如果数据列表包含密钥,例如“-KLdskjdkjkjdjksjdksjdjsdjsjk”firebase将孔列表识别为“HashMap”,则将其识别为“ArrayList”。 我把我的模型改为这个结构:
class ChatPost {
public String id;
public String topic;
public String color;
public HashMap<String, Message> messages;
}
并使用“-KLdskjdkjkjdjksjdksjdjsdjsjk”等密钥添加到其余的聊天消息中。 我的代码现在正在运行。 但我认为这并不明显。
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