java - 如何知道 Firebase 中是否有获取的数据？

Question

我正在尝试寻找是否有办法知道 Firebase 实时数据库中是否已提取数据。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // ARRAY
    accountList = new ArrayList<>();
    // Assigning Object to Controls (bullshit)
    textboxUser = (TextView) findViewById(R.id.textBoxUsername);
    textboxPass = (TextView) findViewById(R.id.textBoxPassword);
    buttonEnter = (Button) findViewById(R.id.buttonEnter);

    postRef = FirebaseDatabase.getInstance().getReference("account");
    dataRefaccount = FirebaseDatabase.getInstance().getReference("account");


    // OnClick Method Button
    buttonEnter.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            try {
                username = textboxUser.getText().toString();
                Query query = FirebaseDatabase.getInstance().getReference("account").orderByChild("username").equalTo(username);
                query.addListenerForSingleValueEvent(valueEventListener);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                Toast.makeText(getApplicationContext(), getted, Toast.LENGTH_LONG).show();
            }



        }
    });
}

ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        for (DataSnapshot data : dataSnapshot.getChildren()) {
            if (data.child(username).exists()) {
                getted = "yes";
            } else {
                getted = "No";
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Toast.makeText(getApplicationContext(), "error", Toast.LENGTH_LONG).show();
    }
};

setter/getter 始终为“NO”。

Answer 1

你应该尝试一下这个。首先确保您在查询响应中没有收到任何错误。

Query query = FirebaseDatabase.getInstance().getReference().child("account").orderByChild("username").equalTo(username);

ValueEventListener valueEventListener = new ValueEventListener() { 
    @Override 
    public void onDataChange(DataSnapshot dataSnapshot) { 
        if (dataSnapshot.getValue() != null && dataSnapshot.getChildrenCount() > 0) {
           for (DataSnapshot data : dataSnapshot.getChildren()) {

                // I'm sure you are looking for below line.. Go and try this.
                if (data.child("username").getValue().toString().equal(username) ) {
                  getted = "yes";
                  break;
                } else {
                  getted = "No";
                }
           }
        } else {
            getted = No value available;
        }
        Toast.makeText(getApplicationContext(), "getted : " + getted, Toast.LENGTH_LONG).show();
    } 

    @Override 
    public void onCancelled(DatabaseError databaseError) { 
        Toast.makeText(getApplicationContext(), "error", Toast.LENGTH_LONG).show(); 
    } 
};

仅供引用:Firebase 调用是异步调用，因此单击按钮时的 finally 子句将始终在 Firebase 响应之前执行。因此，尝试从那里删除 try-catch 并使用上面的代码来打印获取的值。