当我尝试将数据从Firebase数据库添加到firebaseViewHolder时，Android App不断停止

Question

我正在开发食谱书应用程序。 我的数据结构如下：

 Reference
   - users
     -53
     -movies
       -id1
          (-name
          -rating
          -ingredients(list)
          -recipe
          -photo)
       -id2 (....)

数据已正确添加，但是当我使用以下代码进行检索时，该应用程序停止了。 我的模型课是Recipe 。

1. 我需要创建一个网格结构来显示所有碗碟。 我认为这段代码应达到目的，但事实并非如此。 我究竟做错了什么？

2. 当用户单击特定菜肴时，应显示该菜肴的配方和其他详细信息。 如何在Firebase中进行这种选择性检索？

    package foodelicious.com.foodfinal; public class MainActivity extends AppCompatActivity { private FloatingActionButton fab; ScaleAnimation shrinkAnim; private RecyclerView mRecyclerView; private StaggeredGridLayoutManager mLayoutManager; private TextView tvNoRecipes; private ImageView DPoster; private TextView DMovieName,DIngredients,DRecipeTitle,DRecipe; private RatingBar Drate; //Getting reference to Firebase Database FirebaseDatabase database = FirebaseDatabase.getInstance(); DatabaseReference mDatabaseReference = database.getReference(); private static final String userId = "53"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //Initializing our Recyclerview mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view); tvNoRecipes = (TextView) findViewById(R.id.tv_no_recipes); DPoster=(ImageView) findViewById(R.id.Dposter); DIngredients=(TextView) findViewById(R.id.Ding); //scale animation to shrink floating actionbar shrinkAnim = new ScaleAnimation(1.15f, 0f, 1.15f, 0f, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f); if (mRecyclerView != null) { //to enable optimization of recyclerview mRecyclerView.setHasFixedSize(true); } //using staggered grid pattern in recyclerview mLayoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL); mRecyclerView.setLayoutManager(mLayoutManager); //Say Hello to our new FirebaseUI android Element, ie, FirebaseRecyclerAdapter FirebaseRecyclerAdapter<Recipe,RecipeViewHolder> adapter = new FirebaseRecyclerAdapter<Recipe, RecipeViewHolder>( Recipe.class, R.layout.recipe_board_item, RecipeViewHolder.class, //referencing the node where we want the database to store the data from our Object mDatabaseReference.child("users").child(userId).child("movies").getRef() ) { @Override protected void populateViewHolder(final RecipeViewHolder viewHolder, Recipe model, int position) { if(tvNoRecipes.getVisibility()== View.VISIBLE){ tvNoRecipes.setVisibility(View.GONE); } viewHolder.tvRecipeName.setText(model.getRecipeName()); viewHolder.ratingBar.setRating(model.getRecipeRating()); Picasso.with(MainActivity.this).load(model.getRecipePoster()).into(viewHolder.ivRecipePoster); viewHolder.ivRecipePoster.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { setContentView(R.layout.recipe_details); } }); } }; mRecyclerView.setAdapter(adapter); fab = (FloatingActionButton) findViewById(R.id.fab); fab.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { getSupportFragmentManager().beginTransaction() .replace(R.id.frame_container, new AddRecipeFragment()) .addToBackStack(null) .commit(); //animation being used to make floating actionbar disappear shrinkAnim.setDuration(400); fab.setAnimation(shrinkAnim); shrinkAnim.start(); shrinkAnim.setAnimationListener(new Animation.AnimationListener() { @Override public void onAnimationStart(Animation animation) { } @Override public void onAnimationEnd(Animation animation) { //changing floating actionbar visibility to gone on animation end fab.setVisibility(View.GONE); } @Override public void onAnimationRepeat(Animation animation) { } }); } }); } @Override public void onBackPressed() { super.onBackPressed(); if (fab.getVisibility() == View.GONE) fab.setVisibility(View.VISIBLE); } //ViewHolder for our Firebase UI public static class RecipeViewHolder extends RecyclerView.ViewHolder{ TextView tvRecipeName; RatingBar ratingBar; ImageView ivRecipePoster; public RecipeViewHolder(View v) { super(v); tvRecipeName = (TextView) v.findViewById(R.id.iv_dish_name); ratingBar = (RatingBar) v.findViewById(R.id.rating_bar); ivRecipePoster = (ImageView) v.findViewById(R.id.iv_dish_poster); } } } 

LOGCAT

10-05 16：43：08.462 30349-30479 / foodelicious.com.foodfinal D / FA：已连接到远程服务10-05 16：43：08.463 30349-30479 / foodelicious.com.foodfinal V / FA：处理排队服务任务：1 10-05 16：43：13.592 30349-30479 / foodelicious.com.foodfinal V / FA：不活动，与服务断开连接10-05 16：43：21.549 30349-30354 / foodelicious.com.foodfinal I / art ：执行部分代码缓存收集，代码= 29KB，数据= 29KB 10-05 16：43：21.550 30349-30354 / foodelicious.com.foodfinal I / art：代码缓存收集后，代码= 29KB，数据= 29KB 10-05 16：43：21.550 30349-30354 / foodelicious.com.foodfinal I / art：将代码缓存容量增加到128KB 10-05 16：43：21.617 30349-30349 / foodelicious.com.foodfinal D / AndroidRuntime：关闭VM 10- 05：43：21.625 30349-30349 / foodelicious.com.foodfinal E / AndroidRuntime：致命例外：主进程：foodelicious.com.foodfinal，PID：30349 com.google.firebase.database.DatabaseException：类foodelicious.com.foodfinal .models.Recipe缺少构造函数 在com.google.android.gms.internal.zzbqi $ zza.zzaG（未知来源）com.google.android.gms.internal.zzbqi $ zza.zze（未知来源）处没有参数。 com上com.google.android.gms.internal.zzbqi.zzb（未知源）的com.google.android.gms.internal.zzbqi.zza（未知源）的gms.internal.zzbqi.zze（未知源）。 com.firebase.ui.database.FirebaseRecyclerAdapter.getItem（FirebaseRecyclerAdapter.java:136）上com.firebase.ui.database.FirebaseRecyclerAdapter.parseSnapshot（FirebaseRecyclerAdapter.java:147）上的google.firebase.database.DataSnapshot.getValue（未知源） ）在com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder（FirebaseRecyclerAdapter.java:176）在android.support.v7.widget.RecyclerView $ Adapter.onBindViewHolder（RecyclerView.java:6476）在android.support.v7.widget处。 android.support.v7.widget.RecyclerView $ Recycler.tryBindViewHolderByDeadline（RecyclerView.java:5452）上的RecyclerView $ Adapter.bindViewHolder（RecyclerView.java:6509） android.support.v7.widget.Recycler.v7.widget.RecyclerView $ Recycler.tryGetViewHolderForPositionByDeadline（RecyclerView.java:5718）位于android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5557） android.support.v7.widget.LayoutState.next（LayoutState.java:100）处的.getViewForPosition（RecyclerView.java:5553）android.support.v7.widget.StaggeredGridLayoutManager.fill（StaggeredGridLayoutManager.java:1570）在android.support.v7.widget.StaggeredGridLayoutManager.onLayoutChildren（StaggeredGridLayoutManager.java:604）上的support.v7.widget.StaggeredGridLayoutManager.onLayoutChildren（StaggeredGridLayoutManager.java:682）在android.support.v7.widget.RecyclerView.dispatchLayoutLayout2（RecyclerView。 android.support.v7.widget.RecyclerView.dispatchLayout（RecyclerView.java:3410）上的java：3693）android.support.v7.widget.RecyclerView.consumePendingUpdateOperations（RecyclerView.java:1710）上android.support.v7.widget .RecyclerView $ 1.run（RecyclerView.java： 346），位于android.view.Choreographer $ CallbackRecord.run（Choreographer.java:871），位于android.view.Choreographer.doCallbacks（Choreographer.java:683），位于android.view.Choreographer.doFrame（Choreographer.java:616）， android.os.Handler.dispatchMessage（Handler.java:95）上的android.os.Handler.handleCallback（Handler.java:751）上的android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:857） .Looper.loop（Looper.java:154）在android.app.ActivityThread.main（ActivityThread.java:6123）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:867）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:757）

Answer 1

错误：

com.google.firebase.database.DatabaseException：类foodelicious.com.foodfinal.models.Recipe缺少一个没有参数的构造函数

解决方案 ：将默认（无参数）构造函数添加到类Recipe

public class Recipe ... {

   public Recipe() {
       //
   }


}