无法从 Firebase 将数据显示为 ListView

Posted 2023-04-19

【中文标题】无法从 Firebase 将数据显示为 ListView

【英文标题】：Fail to display data as ListView from Firebase

【发布时间】：2014-03-04 19:16:54

【问题描述】：

我的目标只是从 Firebase 检索数据，然后在 android 中将其作为 ListView 输出（无需将任何内容推回数据库）。我尝试从 AndroidChat 示例中学习，并创建了自己的类和自定义列表适配器类，而不是 Chat.java 和 ChatListAdapter.java（如在原始示例中）。我还更改了对 Firebase 的引用，并将我的数据结构类似于 https://android-chat.firebaseio-demo.com/ 的数据结构。下面是我的数据结构：（下面的一切都和AndroidChat的例子一样，只是变量名不同）

我自己的班级：

package com.firebase.androidchat;


public class MenuItem 

    private String food;
    private String weekDay;

    // Required default constructor for Firebase object mapping
    @SuppressWarnings("unused")
    private MenuItem()  

    MenuItem(String food, String weekDay) 
        this.food = food;
        this.weekDay = weekDay;
    

    public String getFood() 
        return food;
    

    public String getWeekDay() 
        return weekDay;
    

我自己的自定义列表适配器类：

package com.firebase.androidchat;

import android.app.Activity;
import android.view.View;
import android.widget.TextView;
import com.firebase.client.Query;

public class MenuListAdapter extends FirebaseListAdapter<MenuItem> 

    public MenuListAdapter(Query ref, Activity activity, int layout) 
        super(ref, MenuItem.class, layout, activity);
    

    @Override
    protected void populateView(View view, MenuItem item) 
        // Map a MenuItem object to an entry in our listview
        String weekDay = item.getWeekDay();
        TextView authorText = (TextView)view.findViewById(R.id.author);
        authorText.setText(weekDay + ": ");
        ((TextView)view.findViewById(R.id.message)).setText(item.getFood());
    

我的 MainActivity 简介：

public class MainActivity extends ListActivity 

    // TODO: change this to your own Firebase URL
    private static final String FIREBASE_URL = "https://barlaurea.firebaseio.com/";

    private Firebase ref;
    private ValueEventListener connectedListener;
    private MenuListAdapter menuListAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);       
        // Setup our Firebase ref
        ref = new Firebase(FIREBASE_URL).child("menu");
    

    @Override
    public void onStart() 
        super.onStart();
        // Setup our view and list adapter. Ensure it scrolls to the bottom as data changes
        final ListView listView = getListView();
        // Tell our list adapter that we only want 50 messages at a time
        menuListAdapter = new MenuListAdapter(ref.limit(50), this, R.layout.chat_message);
        listView.setAdapter(menuListAdapter);

        menuListAdapter.registerDataSetObserver(new DataSetObserver() 
            @Override
            public void onChanged() 
                super.onChanged();
                listView.setSelection(menuListAdapter.getCount() - 1);
            
        );

当我启动“运行”按钮时，我的设备显示一条 toast 消息“已连接到 Firebase”，但屏幕保持空白，然后在几秒钟后崩溃，并显示一条 toast“不幸的是，Firebase 聊天已停止”。我在这里错过了什么？谢谢！

编辑：这是我的 LogCat 视图：在“FAIL EXCEPTION: main line”处一切都变红了 原来的 AndroidChat 在我的设备上也可以正常运行..

02-07 16:17:35.105: D/dalvikvm(31766): GC_CONCURRENT freed 313K, 16% free 7795K/9223K, paused 14ms+16ms, total 65ms
02-07 16:17:36.000: D/dalvikvm(31766): GC_CONCURRENT freed 494K, 17% free 7874K/9479K, paused 2ms+3ms, total 34ms
02-07 16:17:36.365: D/dalvikvm(31766): GC_CONCURRENT freed 482K, 17% free 7923K/9543K, paused 19ms+21ms, total 142ms
02-07 16:17:36.495: D/AndroidRuntime(31766): Shutting down VM
02-07 16:17:36.495: W/dalvikvm(31766): threadid=1: thread exiting with uncaught exception (group=0x41fb02a0)
02-07 16:17:36.520: E/AndroidRuntime(31766): FATAL EXCEPTION: main
02-07 16:17:36.520: E/AndroidRuntime(31766): com.firebase.client.FirebaseException: Failed to bounce to type
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:185)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.firebase.androidchat.FirebaseListAdapter$1.onChildAdded(FirebaseListAdapter.java:63)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.firebase.client.core.ChildListenerContainer$1.run(ChildListenerContainer.java:52)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at android.os.Handler.handleCallback(Handler.java:615)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at android.os.Looper.loop(Looper.java:137)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at android.app.ActivityThread.main(ActivityThread.java:4947)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at java.lang.reflect.Method.invokeNative(Native Method)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at java.lang.reflect.Method.invoke(Method.java:511)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at dalvik.system.NativeStart.main(Native Method)
02-07 16:17:36.520: E/AndroidRuntime(31766): Caused by: com.shaded.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "weekday" (class com.firebase.androidchat.MenuItem), not marked as ignorable (2 known properties: , "weekDay", "food"])
02-07 16:17:36.520: E/AndroidRuntime(31766):  at [Source: java.io.StringReader@42826fc8; line: 1, column: 13] (through reference chain: com.firebase.androidchat.MenuItem["weekday"])
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.DeserializationContext.reportUnknownProperty(DeserializationContext.java:555)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:708)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1160)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:315)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.shaded.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2034)
02-07 16:17:36.520: E/AndroidRuntime(31766):    at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:181)
02-07 16:17:36.520: E/AndroidRuntime(31766):    ... 11 more

【问题讨论】：

当崩溃发生时你能发布你的 logcat 输出吗？

嗨@KhawarRaza，感谢您指出，我已将其附加到问题中。

【参考方案1】：

答案已经在这里找到了：

Firebase's AndroidChat example: Failed to bounce to type

在这种情况下，我应该在 firebase 实例中输入 weekDay 而不是 weekday。