Firebase DataSnapshot Null值 [英] Firebase DataSnapshot Null values

问题描述

我的应用程序允许您将播放器添加到节点，一旦添加了播放器，我将使用以下方法通过phoneNum搜索以查看该播放器是否在用户"节点中.

My app allows you to add a Player to a node, once they have been added I am using the below method to search by phoneNum to see if that player exists in the 'users' node.

我遇到麻烦的地方是，我需要能够从找到的匹配节点内的用户的数据快照中访问值.例如返回用户ID的值.当我尝试这样做时，它一直显示为空值，而当我尝试登录到控制台时，它抱怨说这是一个空值，这是没有意义的，因为if语句应该注意这一点.

Where I am having trouble is that I need to be able to access the values from the datasnapshot for the user within the found matching node. e.g.return the value of the user id. When I attempt this it keeps showing as a null value and when I try to log to the console it complains that it is a null value which doesn't make sense as the if statement should take care of this.

该方法能够找到用户节点中是否存在玩家，并显示一条Toast消息来表明这一点.

The method is able to find if a player exists in the the users node and displays a Toast message to indicate this.

代码:

public void checkPlayerNum(final String phoneNum) {
        DatabaseReference mDatabaseReference =


         FirebaseDatabase.getInstance().getReference().child("users");

    if (!TextUtils.isEmpty(phoneNum)) {
        final Query phoneNumReference = mDatabaseReference.orderByChild("phoneNum").equalTo(phoneNum);

        ValueEventListener phoneNumValueEventListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.getValue() != null) {
                   // String key = String.valueOf(dataSnapshot.getValue());
                   User mUser = dataSnapshot.getValue(User.class);

                    String uId = mUser.getUid();

                  //  Log.d("TAG",uId);
                    Toast.makeText(getApplicationContext(), "* found **"+ uId , Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(getApplicationContext(), "****NOT FOUND****", Toast.LENGTH_LONG).show();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {}
        };

        phoneNumReference.addListenerForSingleValueEvent(phoneNumValueEventListener);


    } else {
        Log.e("Error","phoneNum is null");
    }
}

推荐答案

final Query query = mFirebaseDatabase.orderByChild("phoneNum").equalTo("userPhoneNumber");
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()) {
                    //here means the value exist
                    //do whatever you want to do
                } else {
                    //here means the value not exist
                    //do whatever you want to do
                }
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {
            }
        });

使用它来检查数据是否存在.

Use this to check whether the data exist or not.

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