java如何根据条件从firebase数据库获取图像url并将其加载到ImageView中？

Question

我对安卓系统还不熟悉，并且一直在关注以下问题-

My Firebase Database

在JSON中：

{ "-LwDpiyCDf8tsjTfTF3Q" : { "productImage" : "https://firebasestorage.googleapis.com/v0/b/bookmybook-13560.appspot.com/o/bmbuploads%2F1576501910798.jpg?alt=media&token=a431aec5-0994-4acf-b597-e31b87775ac8", "productName" : "image" }, "-LwDsEXofrJaz9SAjPi4" : { "productImage" : "https://firebasestorage.googleapis.com/v0/b/bookmybook-13560.appspot.com/o/bmbuploads%2F1576502569064.jpg?alt=media&token=573bcfc0-d29e-4e8c-9076-af2868c1c7a5", "productName" : "mgj" } }

我的代码中有产品名称，我希望通过将产品名称作为WHERE条件传递来获取图像（在本例中为productImage），并最终将该图像加载到ImageView中

我尝试使用以下代码：

Query query = databaseReference.child("bmbuploads").orderByChild("productName").equalTo("image");
query.addValueEventListener(new ValueEventListener() {

            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

我不知道我提出的问题是否正确。而且，即使在搜索了很多之后，我也不知道在onDataChange（）方法中要写什么代码

请在这方面指导我

Answer 1

查询在onDataChange中是正确的。您需要从数据库中检索值：

Query query = databaseReference.child("bmbuploads").orderByChild("productName").equalTo("image");
query.addValueEventListener(new ValueEventListener() {

            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot ds :dataSnapshot.getChildren()) {
              String productUrl = ds.child("productImage").getValue(String.class);

            }
         } 

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

添加对节点bmbuploads的引用后，需要迭代才能检索子节点productImage

Answer 2

1 -> get all product first try below code for that
2 -> than after you get both product and product image

==> if want to get product by query you need to store details with key in some other entity that have key of product and productname only.

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference allProducts = rootRef.child("bmbuploads");
addressRef.addListenerForSingleValueEvent(valueEventListener);
List<Products> listAllProduct = new List<Products>



ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
         Log.d(TAG, "total days count: " + dataSnapshot.getChildrenCount());
        // dataSnapshot.getChildren()  give all the days e.g day 1,day 2  // you can get your count here
          for(DataSnapshot ds : dataSnapshot.getChildren()) {
               String key = ds.getKey();  // get key as day 1 

            // add one more observer that give you days matches e.g  
            DatabaseReference childRef = rootRef.child("bmbuploads").child(key);  //where key = e.g day 1                  
            // add new listent that give you detail of address 
            childRef.addListenerForSingleValueEvent(productValueventListner);   // This value event lister give you child matches  

            /**
            * For matches add dayvalueevent listent that give you all matches count.
            **/

        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};



// give all products
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
         Log.d(TAG, "total days count: " + dataSnapshot.getChildrenCount());
        // dataSnapshot.getChildren()  give all the days e.g day 1,day 2  // you can get your count here
           Products producs = dataSnapshot.getValue(Products.class);
           listAllProduct.add(producs);  // you go all product here
           Log.d("allProducts",listAllProduct.toString());

    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};


public static class Products {

  public String productImage;
  public String productName;


    public String getProductImage() {
        return productImage;
    }

    public void setProductImage(String productImage) {
        this.productImage = productImage;
    }

    public String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }

}

Answer 3

要获取productImage属性的值，请使用以下代码行：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("bmbuploads").orderByChild("productName").equalTo("image");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String productImage = ds.child("productImage").getValue(String.class);
            Log.d(TAG, productImage);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
query.addListenerForSingleValueEvent(valueEventListener);

请参见，即使要返回单个结果，也必须使用getChildren()方法循环productImage对象。此对象应包含对象列表。即使只有一个结果，也需要迭代