Android 和 Firebase 将 EditText 与实时数据库子值进行比较

Question

This question has been asked at: Comparing EditText string with firebase database's child value and I am using that as a guide but coming into problems which were not solved there. I know Firebase offers authentication options, but I need to use realtime for the moment. I am looking to compare 2 values entered in my username and password EditTexts to the child values in my realtime database "Users".

When i run my code I get an

Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

I'm assuming that either/both username1 and/or password1 are null and this is why my code is failing to run.

logUsername = findViewById(R.id.etLoginUsers);
logPassword = findViewById(R.id.etLoginPassword);

FirebaseApp.initializeApp(this);
final DatabaseReference mDatabaseRef = FirebaseDatabase.getInstance().getReference().child("Users");

    btnLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

                final String username = logUsername.getText().toString().trim();
                final String password = logPassword.getText().toString().trim();
                mDatabaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        String username1 = dataSnapshot.child("username").getValue().toString();
                        String password1 = dataSnapshot.child("password").getValue().toString();

                        if (username.equals(username1) & password.equals(password1)){
                            Intent intSignIn = new Intent(MainActivity.this, HomeActivity.class);
                            startActivity(intSignIn);
                        } else {
                            Toast.makeText(MainActivity.this, "Incorrect Login Details", Toast.LENGTH_SHORT).show();
                        }
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {

                    }
                });

. I have both my read and write rules set to true. I'm new to coding so any help would be greatly appreciated. Thanks so much!

Answer 1

The key is in this snippet of code:

final DatabaseReference mDatabaseRef = FirebaseDatabase.getInstance().getReference().child("Users");
mDatabaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        String username1 = dataSnapshot.child("username").getValue().toString();
        String password1 = dataSnapshot.child("password").getValue().toString();

Since you're loading from /Users , the dataSnapshot contains the data for all users. Each user's username and password are in a child node under dataSnapshot , which your code needs to handle.

The simplest way to do that from your current code is:

final DatabaseReference mDatabaseRef = FirebaseDatabase.getInstance().getReference().child("Users");
mDatabaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
            String username1 = userSnapshot.child("username").getValue(String.class);
            String password1 = dataSnapshot.child("password").getValue(String.class);
        }

The big differences here are:

• I loop over the child nodes of the data snapshot to get to the snapshot for each individual user.
• I use getValue(String.class) , which will only return a value if username exists.