如何检查Firebase数据类Android中是否已存在值

问题描述

我要检查Firebase数据库中是否已经存在总线号.

I want to check if the bus number already exists in the database of Firebase.

这是我的示例代码.我一直在搜索过去的日子，但找不到合适的代码来实现此目的.

Here's my sample code. I've been searching for the past days but I can't find the right code to do so.

ref = new Firebase(Config.FIREBASE_URL);
postRef = ref.child("BusNumber");

busNum = edtBus.getText().toString().trim();
route1 = route.trim();
seat = edtSeat.getText().toString().trim();

if (!busNum.isEmpty() && !route1.isEmpty() && !seat.isEmpty()) {
    postRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.child(busNum).exists()) {
                edtBus.setError("Bus number already exists.");
                edtBus.setText("");
            } else {
                busNumber = new BusNumber();
                busNumber.setBusNum(busNum);
                busNumber.setRoute(route1);
                busNumber.setNumSeat(seat);
                postRef.push().setValue(busNumber);
                edtBus.setText("");
                edtSeat.setText("");
                Toast.makeText(AddBusActivity.this, "Saving successful!", Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            Toast.makeText(AddBusActivity.this, "Error", Toast.LENGTH_SHORT).show();
            Toast.makeText(AddBusActivity.this, firebaseError.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });

} else {
    Toast.makeText(AddBusActivity.this, "Please complete the information", Toast.LENGTH_SHORT).show();
}

有人可以帮我解决这个问题吗?提前致谢.无论if语句正确与否，我的问题还在于为什么postRef.addListenerForSingleValueEvent ...不起作用?我尝试测试一些吐司消息，但消息不会弹出.

Can somebody help me with this matter? Thanks in advance.Whether the if statement is correct or not, also my problem is why does the postRef.addListenerForSingleValueEvent...doesn't work? I tried to test some toast message but the message won't pop out.

推荐答案

您的方法是错误的.

执行此操作dataSnapshot.child(busNum).exists()时，它将在键部分为-kasajdh...的位置查找busNum.

When you are doing this dataSnapshot.child(busNum).exists(), it's looking for the busNum in the key section, where your keys are -kasajdh....

因此，您可以做的是获取iterable，现在当您寻找data.child(busNum).exists()与值有关

So instead what you can do is, get the iterable, now when you look fordata.child(busNum).exists() it relates to the value

   postRef.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot data: dataSnapshot.getChildren()){
                    if (data.child(busNum).exists()) {
                        //do ur stuff
                    } else {
                       //do something if not exists
                    }
                  }
                }

                @Override
                public void onCancelled(FirebaseError firebaseError) {

                }
            });

这篇关于如何检查Firebase数据类Android中是否已存在值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！