如何使用firebase android在多个节点中查询特定的子值 [英] How to query a specific child value in multiple nodes with firebase android

问题描述

我想查询多个节点中的特定子值，以通过FirebaseListAdapter将其填充到列表视图中。
我传递一个firebase参考FirebaseListAdapter方法来听，这是在下面的图片中的红色矩形，
和我想填充列表视图的值只有类别键。它们在下图中的绿色矩形中。

我的代码在这里：

  catgoryList =（ListView）findViewById（R.id.catList）; 
 rootRef = FirebaseDatabase.getInstance（）。getReference（）; 
 restaurantMenuRef = rootRef.child（menu）。child（restaurantID）; 
 
 FirebaseListAdapter< String> listAdapter = new FirebaseListAdapter< String> 
（this，String.class，R.layout.menu_list_item，restaurantMenuRef）{
 @Override 
 protected void populateView（View v，String s，int position）{
 TextView menuName =（TextView）v.findViewById（R.id.menuName）; 
 menuName.setText（s）; 
} 
}; 
 catgoryList.setAdapter（listAdapter）; 
  

和 $ b您需要重写 FirebaseListAdapter.parseDataSnapshot（），以从中提取正确的值。 $ b

解决方案 DataSnapshot ：

  FirebaseListAdapter< String> listAdapter = new FirebaseListAdapter< String> 
（this，String.class，R.layout.menu_list_item，restaurantMenuRef）{
 
 @Override 
 protected String parseSnapshot（DataSnapshot snapshot）{
 return snapshot.child （ 类别）的getValue（String.class）; 
 
 $ b @Override 
 protected void populateView（View v，String s，int position）{
 TextView menuName =（TextView）v.findViewById（R.id .menuName）; 
 menuName.setText（s）; 
} 
}; 
  

I want to query a specific child value in multiple nodes, to populate them in a list view by FirebaseListAdapter. I'm passing a firebase reference to FirebaseListAdapter method to listen to, which is in red rectangle in the picture below, And I want to populate in the list view the values of the "category" key only. which are in green rectangle in the picture below.

My code is here:

    catgoryList = (ListView) findViewById(R.id.catList);
    rootRef = FirebaseDatabase.getInstance().getReference();
    restaurantMenuRef = rootRef.child("menu").child(restaurantID);

    FirebaseListAdapter<String> listAdapter = new FirebaseListAdapter<String>
            (this, String.class, R.layout.menu_list_item, restaurantMenuRef ) {
        @Override
        protected void populateView(View v, String s, int position) {
            TextView menuName = (TextView)v.findViewById(R.id.menuName);
            menuName.setText(s);
        }
    };
    catgoryList.setAdapter(listAdapter);

And the layout for the listView containing a TextView to display the category name.

解决方案

You'll need to override FirebaseListAdapter.parseDataSnapshot() to extract the right value from the DataSnapshot:

FirebaseListAdapter<String> listAdapter = new FirebaseListAdapter<String>
        (this, String.class, R.layout.menu_list_item, restaurantMenuRef ) {

    @Override
    protected String parseSnapshot(DataSnapshot snapshot) {
        return snapshot.child("category").getValue(String.class);
    }

    @Override
    protected void populateView(View v, String s, int position) {
        TextView menuName = (TextView)v.findViewById(R.id.menuName);
        menuName.setText(s);
    }
};

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