无法将类型为java.util.ArrayList的对象转换为类型model。

Question

我正在尝试从Firebase加载数据到RecycleView，但是遇到了转换错误。

com.google.firebase.database.DatabaseException: Can't convert object of type java.util.ArrayList to type uk.co.stableweb.kithunugee.model.Hymn
     at com.google.android.gms.internal.zzaix.zzd(Unknown Source)
     at com.google.android.gms.internal.zzaix.zzb(Unknown Source)
     at com.google.android.gms.internal.zzaix.zza(Unknown Source)
     at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
     at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)  
     at com.firebase.ui.database.FirebaseRecyclerAdapter.parseSnapshot(FirebaseRecyclerAdapter.java:147)
     at com.firebase.ui.database.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:136)
     at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:176)
     at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5471)
     at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5504)
     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4741)
     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4617)
     at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1994)
     at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1390)
     at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1353)
     at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:574)
     at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3028)
     at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2625)
     at android.view.View.measure(View.java:18850)
     at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:668)
     at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
     at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1192)
     at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:733)
     at android.view.View.measure(View.java:18850)
     at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1075)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
     at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
     at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
     at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
     at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
     at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5956)
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
     at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2671)
     at android.view.View.measure(View.java:18850)
     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2107)

这是我从RecyclerView加载数据的方式。

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
mRecyclerViewAdapter = new FirebaseRecyclerAdapter<Hymn, HymnHolder>(Hymn.class, R.layout.hymn_row, HymnHolder.class, ref) {
       @Override
       protected void populateViewHolder(HymnHolder viewHolder, Hymn hymn, int position) {
              viewHolder.setTitle(hymn.getTitle());
              viewHolder.setIndex(String.valueOf(hymn.getIndex()));
      }
};

// Scroll to bottom on new messages
mRecyclerViewAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
       @Override
       public void onItemRangeInserted(int positionStart, int itemCount) {
              mLayoutManager.smoothScrollToPosition(recyclerView, null, mRecyclerViewAdapter.getItemCount());
       }
});

recyclerView.setAdapter(mRecyclerViewAdapter);

我的ViewHolder类是：

public class HymnHolder extends RecyclerView.ViewHolder {
    View mView;

    public HymnHolder(View itemView) {
        super(itemView);
        mView = itemView;
    }

    public void setTitle(String name) {
        TextView field = (TextView) mView.findViewById(R.id.title);
        field.setText(name);
    }

    public void setIndex(String index) {
        TextView field = (TextView) mView.findViewById(R.id.index);
        field.setText(index);
    }
}

这是我的模型。

public class Hymn {
    private int index;
    private String title;
    private String content;

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

}

这是我的 Firebase 数据库的结构。

我参考了this Firebase UI 教程。之前有一些关于这个问题的问题，但对我来说并不清楚。如果你有任何提示，那将非常有帮助。

- Isuru

---

我不这么认为，但是我已经添加了完整的错误代码。感谢您的帮助！ - Isuru

好的，我也会尝试。谢谢！ - Isuru

完成后，编辑问题并说明哪一行代码导致错误，并写下注释和@提及我。祝好运。 - Vucko

我不熟悉Firebase，但根据您展示的结构，似乎“geethika”正在返回一个数组（索引1、2），而您期望的是一个对象Hymn。 - Rocel

你正在树中读取高了一个级别。从你的数据结构来看，你想要 DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("geethika"); 在那个节点下，每个子节点似乎与你的 Hymn 类匹配。 - Frank van Puffelen

Answer 1

更改您的数据库引用

旧代码

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();

新代码

 mDatabaseReference = FirebaseDatabase.getInstance().getReference().child("geethik‌​a");

- Rajendra Verma