Android Firebase异常“无法解析类型T"

问题描述

他有一个抽象的通用类"ArticleOrdered"和一个子类"DrinkOrdered"(有关类的声明，请参见下面的代码).如果我创建了DrinkOrdered对象并将其保存在Firebase中，则不会有任何问题.当我尝试执行时:

DrinkOrdered test = dataSnapshot.getValue(DrinkOrdered.class);

要获取对象，我有

java.lang.IllegalStateException: Could not resolve type T

ArticleOrdered类:

public abstract class ArticleOrdered<T extends Article> {
private int quantity;
private T article;
private String note;
private double price;

public ArticleOrdered(int quantity, T article, String note) {
    this.quantity = quantity;
    this.article = article;
    this.note = note;
    this.price = article.getPrice();
}

public ArticleOrdered() {
    //FIREBASE CONSTUCTOR
}

public T getArticle() {
    return article;
}

public void setArticle(T article) {
    this.article = article;
}
...

DrinkOrdered类:

public class DrinkOrdered extends ArticleOrdered<Drink> {

public DrinkOrdered(int quantity, Drink article, String note) {
    super(quantity, article, note);
}

public DrinkOrdered() {
    //FIREBASE CONSTRUCTOR
}

我还有另一个类"PizzaOrdered"(但是现在不重要了)

TestActivity代码:

FirebaseDatabase db = FirebaseDatabase.getInstance();
    DatabaseReference orderRef = db.getReference("prova");
    ValueEventListener listener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            DrinkOrdered a = dataSnapshot.getValue(DrinkOrdered.class);

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.d("PIERF", "onCancelled");
        }
    };
    orderRef.addListenerForSingleValueEvent(listener);

以这种方式声明它们是否正确?对不起，英语不好.

解决方案

我自己使用Jackson编写的以下两行代码来解决了这个问题:

ObjectMapper mapper = new ObjectMapper();
DrinkOrdered a = mapper.convertValue(dataSnapshot.getValue(), DrinkOrdered.class);

hi have an abstract generic class "ArticleOrdered" and a subclass "DrinkOrdered" (see code below for class declaration). If i create a DrinkOrdered object and i save it in Firebase, I have no problems.When i try to execute:

DrinkOrdered test = dataSnapshot.getValue(DrinkOrdered.class);

to get the object, i have

java.lang.IllegalStateException: Could not resolve type T

ArticleOrdered class:

public abstract class ArticleOrdered<T extends Article> {
private int quantity;
private T article;
private String note;
private double price;

public ArticleOrdered(int quantity, T article, String note) {
    this.quantity = quantity;
    this.article = article;
    this.note = note;
    this.price = article.getPrice();
}

public ArticleOrdered() {
    //FIREBASE CONSTUCTOR
}

public T getArticle() {
    return article;
}

public void setArticle(T article) {
    this.article = article;
}
...

DrinkOrdered class:

public class DrinkOrdered extends ArticleOrdered<Drink> {

public DrinkOrdered(int quantity, Drink article, String note) {
    super(quantity, article, note);
}

public DrinkOrdered() {
    //FIREBASE CONSTRUCTOR
}

I have another class "PizzaOrdered" (but it is not important now)

TestActivity code:

FirebaseDatabase db = FirebaseDatabase.getInstance();
    DatabaseReference orderRef = db.getReference("prova");
    ValueEventListener listener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            DrinkOrdered a = dataSnapshot.getValue(DrinkOrdered.class);

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.d("PIERF", "onCancelled");
        }
    };
    orderRef.addListenerForSingleValueEvent(listener);

is it correct to declare them in this way? Sorry for bad english.

解决方案

I solved it by myself, using Jackson with these 2 lines of code:

ObjectMapper mapper = new ObjectMapper();
DrinkOrdered a = mapper.convertValue(dataSnapshot.getValue(), DrinkOrdered.class);

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