android - 从 firebase 检索多个数据

Question

嘿，我对 firebase 和编程也比较陌生，所以如果这是一个愚蠢的问题，我很抱歉。我正在努力检索食谱

上面是来自 firebase 的数据树，下面是来自 MainActivity 的代码

       package com.example.myapplicationdatatest;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

import com.google.firebase.FirebaseApp;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {

    private TextView category;
    private TextView cookinTime;
    private TextView description;
    private TextView ingridients;
    private TextView nameOfRecipe;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.activity_main );
        category = findViewById( R.id.category );
        cookinTime = findViewById( R.id.cookingTime );
        description = findViewById( R.id.description );
        ingridients = findViewById( R.id.ingridients );
        nameOfRecipe = findViewById( R.id.nameOfRecipe );
        FirebaseApp.initializeApp( getApplicationContext() );






        FirebaseDatabase.getInstance().getReference().child( "recipes" )
                .addListenerForSingleValueEvent( new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                            Recipe recipe = snapshot.getValue( Recipe.class );

                            category.setText( recipe.getCategory() );
                            cookinTime.setText( recipe.getCookingtime() );
                            description.setText( recipe.getDescription() );
                            ingridients.setText( recipe.getIngredients() );
                            nameOfRecipe.setText( recipe.getIngredients() );
                        }
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {
                    }
                } );
    }





}

布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/category"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

      />

    <TextView
        android:id="@+id/cookingTime"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

    <TextView
        android:id="@+id/description"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

    <TextView
        android:id="@+id/ingridients"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

    <TextView
        android:id="@+id/nameOfRecipe"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

</LinearLayout>

配方类

    package com.example.myapplicationdatatest;

public class Recipe {

    private String category;
    private String cookingtime;
    private String description;
    private String ingredients;
    private String nameOfRecipe;

    public Recipe() {};

    public Recipe(String category, String cookingtime, String description,String ingredients, String nameOfRecipe) {
        this.category=category;
        this.cookingtime=cookingtime;
        this.description=description;
        this.ingredients=ingredients;
        this.nameOfRecipe=nameOfRecipe;
    }

    public String getCategory() {
        return category;
    }

    public String getCookingtime() {
        return cookingtime;
    }

    public String getDescription() {
        return description;
    }

    public String getIngredients() {
        return ingredients;
    }

    public String getNameOfRecipe() {
        return nameOfRecipe;
    }
}

和异常

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapplicationdatatest, PID: 6400
    com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertString(com.google.firebase:firebase-database@@19.1.0:408)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@19.1.0:199)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@19.1.0:178)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(com.google.firebase:firebase-database@@19.1.0:47)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.1.0:586)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.1.0:545)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@19.1.0:415)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@19.1.0:214)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-database@@19.1.0:79)
        at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:firebase-database@@19.1.0:203)
        at com.example.myapplicationdatatest.MainActivity$1.onDataChange(MainActivity.java:53)
        at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@19.1.0:179)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.1.0:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.1.0:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.1.0:55)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

我真的不知道如何检索这些多个分支，尤其是因为我想添加多个食谱

谢谢你的帮助

Answer 1

您收到以下错误:

com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String

因为您的 Recipe 中字段的类型类与数据库中的属性类型不同。你有你的 Recipe对名为 ingredients 的字段进行分类这是类型 String在数据库中我看到这是一个 Map<String, Object>这是不正确的，因此是错误的。字段的类型必须匹配。除此之外，您的数据库中还有一个名为 amountOfIngredients 的属性。你的 Recipe 中实际上缺少它类(class)。要解决此问题，请为您的 Recipe 建模根据数据库中存在的属性类型进行分类，您的问题将得到解决。