无法从 Firebase DB 填充回收器视图

Question

这个问题虽然回答了几次，但都没有解决我的问题。

我有一个只有两个键值对的 firebase 数据库。下面是json.

{
   "route" : {
   "routeA" : {
   "stop" : "Street 1",
   "time" : "11:00 PM"
  }
 }
}

以下是我从firebase DB获取数据的代码

  recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    rootRef = new Firebase("https://listrecycler.firebaseio.com/route/");
}

@Override
protected void onStart() {
    super.onStart();
    itemsRef = rootRef.child("route B");
    Toast.makeText(MainActivity.this, "crossed itemRef", Toast.LENGTH_SHORT).show();
    firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Route, RouteViewHolder>(Route.class, android.R.layout.two_line_list_item, RouteViewHolder.class, itemsRef) {
        @Override
        public void populateViewHolder(RouteViewHolder routeViewHolder, Route route, int i) {
            Toast.makeText(MainActivity.this, "reached populate view holder", Toast.LENGTH_SHORT).show();
            Log.d(TAG, "populateViewHolder: " + route);
            routeViewHolder.place.setText(route.getStop());
            routeViewHolder.time.setText(route.getTime());
        }
    };
    recyclerView.setAdapter(firebaseRecyclerAdapter);

}

public static class RouteViewHolder extends RecyclerView.ViewHolder {

    TextView place;
    TextView time;

    public RouteViewHolder(View itemView) {
        super(itemView);
        place = (TextView) itemView.findViewById(android.R.id.text1);
        time = (TextView) itemView.findViewById(android.R.id.text2);
    }
}

这是 Frank 建议的没有任何 recyclerview 的简单代码。代码工作正常。没有杰克逊错误

 rootRef = new Firebase("https://listrecycler.firebaseio.com/route");

}

@Override
protected void onStart() {
    super.onStart();
    itemsRef = rootRef.child("routeA");

    itemsRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Route routeDetails = dataSnapshot.getValue(Route.class);
            String stop = routeDetails.getStop();
            String time = routeDetails.getTime();
            Toast.makeText(MainActivity.this, "Stop Name:"+ stop+"Time:"+time, Toast.LENGTH_SHORT).show();
            Log.d(TAG, "onDataChange: "+dataSnapshot);
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
}

以下是我的POJO

public class Route {
public String stop;
public String time;

public Route() {
}

public Route(String stop, String time) {
    this.stop = stop;
    this.time = time;
}

public String getStop() {
    return stop;
}

public void setStop(String stop) {
    this.stop = stop;
}

public String getTime() {
    return time;
}

public void setTime(String time) {
    this.time = time;
}
}

代码的问题是当我使用 POJO 时，Jackson 无法反序列化 Firebase 发送的数据。当我使用一个简单的 String class 而不是 Route POJO 时，数据被完美地写入回收器视图项中。下面是错误日志

05-06 22:38:03.724 30051-30051/abc.com.example.vijsu.listrecyclerfirebase E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                        Process: abc.com.example.vijsu.listrecyclerfirebase, PID: 30051
                                                                                        com.firebase.client.FirebaseException: Failed to bounce to type
                                                                                            at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:183)
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.parseSnapshot(FirebaseRecyclerAdapter.java:161)
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:150)
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:190)
                                                                                            at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5465)
                                                                                            at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5498)
                                                                                            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4735)
                                                                                            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4611)
                                                                                            at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1988)
                                                                                            at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1384)
                                                                                            at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1347)
                                                                                            at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:574)
                                                                                            at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3026)
                                                                                            at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2903)
                                                                                            at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1457)
                                                                                            at android.support.v7.widget.RecyclerView.access0(RecyclerView.java:147)
                                                                                            at android.support.v7.widget.RecyclerView.run(RecyclerView.java:285)
                                                                                            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
                                                                                            at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                                                                                            at android.view.Choreographer.doFrame(Choreographer.java:603)
                                                                                            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                                                                                            at android.os.Handler.handleCallback(Handler.java:739)
                                                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                            at android.os.Looper.loop(Looper.java:148)
                                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                                         Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class abc.com.example.vijsu.listrecyclerfirebase.Route] from String value; no single-String constructor/factory method
                                                                                            at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:428)
                                                                                            at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:299)
                                                                                            at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1056)
                                                                                            at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:136)
                                                                                            at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:123)
                                                                                            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:181)
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.parseSnapshot(FirebaseRecyclerAdapter.java:161) 
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:150) 
                                                                                            at com.firebase.ui.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:190) 
                                                                                            at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5465) 
                                                                                            at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5498) 
                                                                                            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4735) 
                                                                                            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4611) 
                                                                                            at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1988) 
                                                                                            at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1384) 
                                                                                            at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1347) 
                                                                                            at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:574) 
                                                                                            at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3026) 
                                                                                            at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2903) 
                                                                                            at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1457) 
                                                                                            at android.support.v7.widget.RecyclerView.access0(RecyclerView.java:147) 
                                                                                            at android.support.v7.widget.RecyclerView.run(RecyclerView.java:285) 
                                                                                            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858) 
                                                                                            at android.view.Choreographer.doCallbacks(Choreographer.java:670) 
                                                                                            at android.view.Choreographer.doFrame(Choreographer.java:603) 
                                                                                            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844) 
                                                                                            at android.os.Handler.handleCallback(Handler.java:739) 
                                                                                            at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                                                            at android.os.Looper.loop(Looper.java:148) 
                                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                                            at java.lang.reflect.Method.invoke(Native Method) 
                                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

我已经刷新了 Firebase 检查的数据，以确保 POJO 和 Firebase DB 中的字符串名称多次匹配。我知道我遗漏了与 POJO 相关的内容，但无法弄清楚。

但是在recycler view下错误依然存在!!!

Answer 1

错误提到这个

Can not instantiate value of type ... Route... no single-String constructor/factory method

所以你可能想添加一个

public class Route {

    public String stop;
    public String time;

    public Route() {}

    public Route(String routeJSON) { 
        // TODO: Parse out JSON object
        // call setters...
    }

    public Route(String stop, String time) {
        this.stop = stop;
        this.time = time;
    }

Answer 2

最愚蠢的错误是我忘记了回收器视图需要一个属性列表并且我有多个属性（停止和时间）显示在一行中。所以我只需要获取 routeA 并将其交给 firebasui 来显示。我在将数据上传到 routeA 时进入了更深层次，而 firebaseui 无法识别这些属性。只有 route 级别的查询足以在单行中显示 stop 和 time 属性。

将其作为一个单独的答案写下来，以帮助像我这样对小而重要的事情一无所知的人。这个概念也是@Frank van Puffelen 对其中一个类似答案发布的答案的一部分。

无法从 Firebase DB 填充回收器视图

Unable to populate recycler viiew from Firebase DB

android

firebase

android-recyclerview

firebase-realtime-database

firebaseui