Android 来自firebase的函数addListenerForSingleValueEvent

使用Firebase数据库。 我有一个数据库，用于存储患者的注册信息。 注册新患者时，我会检查该患者是否已经注册

下面的功能检查此人是否已注册。 我通过“用户/电话号码/患者姓名”来检查这一点。 如果DataSnapshot不为null，则已存在注册

private boolean checkAlreadyRegistered(){

    final boolean[] alreadyRegistered = {false};
    /*Get the reference*/
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users/" + childDetails.getPhone() + "/" + childDetails.getPatientName());
    mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.d(TAG, "onDataChange: " + dataSnapshot);
            if (dataSnapshot.getValue() != null) {

                AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
                builder.setTitle("Record Already Exists");
                builder.setMessage("The current patient is already registered");
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int id) {

                        alreadyRegistered[0] = true;
                    }
                });
                builder.create();
                builder.show();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

            Toast.makeText(getContext(), "Some error occured", Toast.LENGTH_LONG).show();
        }
    });
    return  alreadyRegistered[0];
}

从saveInDatabase调用上述函数

void saveInDatabase(Long patient_id) {


    boolean alreadyRegistered = checkAlreadyRegistered();
    if (alreadyRegistered) {
        resetRegisterFields();
        return;
    }
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Current_registered_users");
    mDatabaseReference.setValue(patient_id + 1);
    childDetails.setPatient_id(patient_id);
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users");
    Log.d(TAG, "saveInDatabase: "+mDatabaseReference);
    mDatabaseReference.child(childDetails.getPhone()).child(childDetails.getPatientName()).child("Registration Details").setValue(childDetails);
    Button bt = (Button) getView().findViewById(R.id.buttonRegister);
    resetRegisterFields();
    progressDialog.dismiss();
    displayPid(patient_id);
    bt.setEnabled(true);
    .
    .
}

我想做的事情-检查是否已经根据电话号码/患者姓名进行了登记，如果没有，请保存详细信息

问题-进行新注册时，会将其添加到数据库中，但之后会显示checkAlreadyRegistered（）->onDataChange中的消息“.已注册”

---

为什么会出现此消息，以及如何解决此问题？

Firebase中的所有数据读取都是异步进行的，因此我建议您将代码更改为如下所示：

private void checkAlreadyRegistered(){

    /*Get the reference*/
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users/" + childDetails.getPhone() + "/" + childDetails.getPatientName());
    mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.d(TAG, "onDataChange: " + dataSnapshot);
            if (dataSnapshot.getValue() != null) {

                AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
                builder.setTitle("Record Already Exists");
                builder.setMessage("The current patient is already registered");
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int id) {
                        resetRegisterFields();
                    }
                });
                builder.create();
                builder.show();
            }
            else
            {
                saveInDatabase(patient_id); //TODO change this accordingly
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

            Toast.makeText(getContext(), "Some error occured", Toast.LENGTH_LONG).show();
        }
    });
}

以及您的保存方法：

void saveInDatabase(Long patient_id) {
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Current_registered_users");
    mDatabaseReference.setValue(patient_id + 1);
    childDetails.setPatient_id(patient_id);
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users");
    Log.d(TAG, "saveInDatabase: "+mDatabaseReference);
    mDatabaseReference.child(childDetails.getPhone()).child(childDetails.getPatientName()).child("Registration Details").setValue(childDetails);
    Button bt = (Button) getView().findViewById(R.id.buttonRegister);
    resetRegisterFields();
    progressDialog.dismiss();
    displayPid(patient_id);
    bt.setEnabled(true);
    .
    .
}

---

您必须等待Firebase的响应。您可以添加一个回调，以便在检索完代码后运行其余的代码。这样做：

private void checkAlreadyRegistered(){

    /*Get the reference*/
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users/" + childDetails.getPhone() + "/" + childDetails.getPatientName());
    mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.d(TAG, "onDataChange: " + dataSnapshot);
            if (dataSnapshot.getValue() != null) {

                AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
                builder.setTitle("Record Already Exists");
                builder.setMessage("The current patient is already registered");
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int id) {
                        resetRegisterFields();
                    }
                });
                builder.create();
                builder.show();
            }
            else
            {
                saveInDatabase(patient_id); //TODO change this accordingly
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

            Toast.makeText(getContext(), "Some error occured", Toast.LENGTH_LONG).show();
        }
    });
}

创建一个名为

ServerCallback

的接口：

public interface ServerCallback
{
    void onSuccess(boolean result);
}

在您的

checkAlreadyRegistered（）

方法中，添加回调，以便在从Firebase检索数据后运行回调：

private void checkAlreadyRegistered(final ServerCallback callback){
    final boolean[] alreadyRegistered = {false};
    /*Get the reference*/
    mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users/" + childDetails.getPhone() + "/" + childDetails.getPatientName());
    mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.d(TAG, "onDataChange: " + dataSnapshot);
            if (dataSnapshot.getValue() != null) {
                AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
                builder.setTitle("Record Already Exists");
                builder.setMessage("The current patient is already registered");
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int id) {

                        alreadyRegistered[0] = true;
                        callback.onSuccess(alreadyRegistered[0]);
                    }
                });
                builder.create();
                builder.show();
            }
            else
               callback.onSuccess(alreadyRegistered[0]);
        }

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

然后在

saveInDatabase（）

中，等待回调，然后运行其余代码：

void saveInDatabase(Long patient_id) {
    boolean alreadyRegistered = checkAlreadyRegistered(new ServerCallback() {
        @Override
        public void onSuccess(boolean result)
        {
            if (alreadyRegistered) {
                resetRegisterFields();
                return;
            }
            mDatabaseReference = FirebaseDatabase.getInstance().getReference("Current_registered_users");
            mDatabaseReference.setValue(patient_id + 1);
            childDetails.setPatient_id(patient_id);
            mDatabaseReference = FirebaseDatabase.getInstance().getReference("Users");
            Log.d(TAG, "saveInDatabase: "+mDatabaseReference);
            mDatabaseReference.child(childDetails.getPhone()).child(childDetails.getPatientName()).child("Registration Details").setValue(childDetails);
            Button bt = (Button) getView().findViewById(R.id.buttonRegister);
            resetRegisterFields();
            progressDialog.dismiss();
            displayPid(patient_id);
            bt.setEnabled(true);
            .
            .
        });
 }

onDataChange（）

异步激发<代码>checkAlreadyRegistered（）在结果可用之前返回。有关详细说明，请参见此答案：因此，从onDataChange（）调用saveInDatabase（）将解决问题，对吗？