如何在Android中查询Firebase数据库-Java 学习之路

我对Android Studio Firebase数据库有疑问 . 我目前正在尝试在查询中设置一个条件，以便为选定的查询发送通知，在这种情况下，在我的Firebase数据库中选择 send notification if MenuId=01 ，希望您能提供帮助，谢谢 .

if (request.getFoods().isEmpty()) {
         Toast.makeText(Cart.this, "Your cart is empty", Toast.LENGTH_SHORT).show();
     } else{

         final DatabaseReference MyMenuId = FirebaseDatabase.getInstance().getReference("foods");
         final Query data = MyMenuId.orderByChild("MenuId").equalTo("01"); // get all node with menuID=01

试图找出如何在此 MenuId=01 上设置一个条件，仅在选择此MenuId时发送通知：

data.addValueEventListener(new ValueEventListener() {
        @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String order_number = String.valueOf(System.currentTimeMillis());
                requests.child(order_number).setValue(request);

                // Delete Cart
                new Database(getBaseContext()).cleanCart();
                Toast.makeText(Cart.this, "You have ordered from menu 1", Toast.LENGTH_SHORT).show();
                finish();
                sendNotificationOrder(order_number);
                Toast.makeText(Cart.this, "You did not order from menuId 1", Toast.LENGTH_SHORT).show();
        }**

2 回答

你不需要把条件只使用addListenerForSingleValueEvent，它只会在找到目标值后执行 . 你正在使用addValueListener，它正在监听节点中的所有值，你想要找到一个值，更好的是使用单值监听器 .

DatabaseReference MyMenuId = FirebaseDatabase.getInstance().getReference("foods").child("MenuId").orderByChild("city").equalTo(
 final Query data = MyMenuId.orderByChild("MenuId").equalTo("01"); // get all node with menuID=01

          data.addListenerForSingleValueEvent(new ValueEventListener() { 
        @Override 
            public void onDataChange(DataSnapshot dataSnapshot) {
                String order_number = String.valueOf(System.currentTimeMillis());
                requests.child(order_number).setValue(request);

                // Delete Cart 
                new Database(getBaseContext()).cleanCart();
                Toast.makeText(Cart.this, "You have ordered from menu 1", Toast.LENGTH_SHORT).show();
                finish();
                sendNotificationOrder(order_number);
                Toast.makeText(Cart.this, "You did not order from menuId 1", Toast.LENGTH_SHORT).show();
        }
}

回复于 2024-04-29T07:58:29+08:00

无论是否有结果，都会调用 onDataChange . 要检查是否有实际结果，请使用 dataSnapshot.exists() ：

data.addValueEventListener(new ValueEventListener() {
    @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
          if (dataSnapshot.exists()) {
            String order_number = String.valueOf(System.currentTimeMillis());
            requests.child(order_number).setValue(request);

            // Delete Cart
            new Database(getBaseContext()).cleanCart();
            Toast.makeText(Cart.this, "You have ordered from menu 1", Toast.LENGTH_SHORT).show();
            finish();
            sendNotificationOrder(order_number);
            Toast.makeText(Cart.this, "You did not order from menuId 1", Toast.LENGTH_SHORT).show();
          }
        }

如果您需要实际处理结果，请记住以下几点 .

对Firebase数据库执行查询时，可能会有多个结果 . 因此快照包含这些结果的列表 . 即使只有一个结果，快照也会包含一个结果的列表 .

因此，您的代码需要通过遍历 dataSnapshot.getChildren() 来处理结果列表：

data.addValueEventListener(new ValueEventListener() {
    @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
          for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
            String order_number = String.valueOf(System.currentTimeMillis());
            requests.child(order_number).setValue(request);

            // Delete Cart
            new Database(getBaseContext()).cleanCart();
            Toast.makeText(Cart.this, "You have ordered from menu 1", Toast.LENGTH_SHORT).show();
            finish();
            sendNotificationOrder(order_number);
            Toast.makeText(Cart.this, "You did not order from menuId 1", Toast.LENGTH_SHORT).show();
          }
        }

回复于 2024-04-29T07:58:29+08:00

如何在Android中查询Firebase数据库

2 回答

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