當我嘗試將數據從Firebase數據庫添加到firebaseViewHolder時，Android App不斷停止

Question

我正在開發食譜書應用程序。 我的數據結構如下：

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

數據已正確添加，但是當我使用以下代碼進行檢索時，該應用程序停止了。 我的模型課是Recipe 。

1. 我需要創建一個網格結構來顯示所有碗碟。 我認為這段代碼應達到目的，但事實並非如此。 我究竟做錯了什么？

2. 當用戶單擊特定菜餚時，應顯示該菜餚的配方和其他詳細信息。 如何在Firebase中進行這種選擇性檢索？

    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：已連接到遠程服務10-05 16：43：08.463 30349-30479 / foodelicious.com.foodfinal V / FA：處理排隊服務任務：1 10-05 16：43：13.592 30349-30479 / foodelicious.com.foodfinal V / FA：不活動，與服務斷開連接10-05 16：43：21.549 30349-30354 / foodelicious.com.foodfinal I / art ：執行部分代碼緩存收集，代碼= 29KB，數據= 29KB 10-05 16：43：21.550 30349-30354 / foodelicious.com.foodfinal I / art：代碼緩存收集后，代碼= 29KB，數據= 29KB 10-05 16：43：21.550 30349-30354 / foodelicious.com.foodfinal I / art：將代碼緩存容量增加到128KB 10-05 16：43：21.617 30349-30349 / foodelicious.com.foodfinal D / AndroidRuntime：關閉VM 10- 05：43：21.625 30349-30349 / foodelicious.com.foodfinal E / AndroidRuntime：致命例外：主進程：foodelicious.com.foodfinal，PID：30349 com.google.firebase.database.DatabaseException：類foodelicious.com.foodfinal .models.Recipe缺少構造函數 在com.google.android.gms.internal.zzbqi $ zza.zzaG（未知來源）com.google.android.gms.internal.zzbqi $ zza.zze（未知來源）處沒有參數。 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處。 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）位於android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5557） android.support.v7.widget.LayoutState.next（LayoutState.java:100）處的.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），位於android.view.Choreographer $ CallbackRecord.run（Choreographer.java:871），位於android.view.Choreographer.doCallbacks（Choreographer.java:683），位於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（本機方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:867）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:757）

Answer 1

錯誤：

com.google.firebase.database.DatabaseException：類foodelicious.com.foodfinal.models.Recipe缺少一個沒有參數的構造函數

解決方案 ：將默認（無參數）構造函數添加到類Recipe

public class Recipe ... {

   public Recipe() {
       //
   }


}