我需要一种检查数据的方法，实时数据库上是否存在

Question

我有一个用于打开更高权限活动布局的二维码布局，我如何在 firebase 数据库上在线制作/搜索代码，如下所示

this what my firebase data look

下面是可以打开新活动的代码，但我希望每个管理员的代码都不同，所以如果管理员退休，我不需要每次都更改应用程序内的代码

public class BarcodeScanner extends AppCompatActivity {

    private CodeScanner mCodeScanner;
    private static final String Code = "newsenyum";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_barcode_scanner);
        CodeScannerView scannerView = findViewById(R.id.scanner_view);
        mCodeScanner = new CodeScanner(this, scannerView);
        mCodeScanner.setDecodeCallback(new DecodeCallback () {
            @Override
            public void onDecoded(@NonNull final Result result) {
               BarcodeScanner.this.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {

                        String codeFromScanner = result.getText(); // initialize the code from scanner

                        if(Code.equals (codeFromScanner.trim ())){
                            redirectToNewActivity ();
                        }else{
                            Toast.makeText (BarcodeScanner.this, "QRCode Tidak Dapat di Gunakan", Toast.LENGTH_SHORT).show ( );
                        }
                    }
                });
            }
        });


        scannerView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mCodeScanner.startPreview();
            }
        });
    }



    private void redirectToNewActivity() {
        startActivity (new Intent (getApplicationContext ( ), AdminUID.class));
        finish ( );
    }

    @Override
    protected void onResume() {
        super.onResume();
        mCodeScanner.startPreview();
    }

    @Override
    protected void onPause() {
        mCodeScanner.releaseResources();
        super.onPause();
    }

}

this is the code

Answer 1

要检查数据库中是否存在特定的条形码，您需要使用 Query 对象。所以请使用以下代码行：

DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference adminRef = db.child("Admin");
Query queryByCode = adminRef.orderByChild("barcode code").equalTo("pa29h9h75dg");
queryByCode.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DataSnapshot> task) {
        if (task.isSuccessful()) {
            DataSnapshot snapshot = task.getResult();
            if(snapshot.exists()) {
                Log.d("TAG", "Barcode already exists.");

                for (DataSnapshot ds : snapshot.getChildren()) {
                    String id = ds.child("id").getValue(String.class);
                    Log.d("TAG", id);
                }
            } else {
                Log.d("TAG", "Barcode doesn't exist.");
            }
        } else {
            Log.d("TAG", task.getException().getMessage()); //Don't ignore potential errors!
        }
    }
});

logcat 中的结果将是：

Lela