@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mAuth = FirebaseAuth.getInstance();
    btRegistro = (Button) findViewById(R.id.bt_registro);
    etUser = (EditText) findViewById(R.id.et_userRegistro);
    etEmail = (EditText) findViewById(R.id.et_correoRegistro);
    etPass = (EditText) findViewById(R.id.et_passwordRegistro);
    //Progreso
    mProgress = new ProgressDialog(this);

    //string
    String name = etUser.getText().toString();
    String email = etEmail.getText().toString();
    String pass = etPass.getText().toString();

    if (!TextUtils.isEmpty(name) && !TextUtils.isEmpty(email) && !TextUtils.isEmpty(pass)){
        //Seteo la barra de progreso
        mProgress.setMessage("Registering, please wait...");
        mProgress.show();
        //Creo el registro para FireBase
        mAuth.createUserWithEmailAndPassword(email,pass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {

            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                mProgress.dismiss(); //quito el Progress dialog
                if (task.isSuccessful()){
                    String user_id = mAuth.getCurrentUser().getUid();
                    Toast.makeText(Registro.this, "Authentication Complete : " + user_id, Toast.LENGTH_SHORT).show();
                    limpiarCampos();
                }else{
                    // If sign in fails, display a message to the user.
                    //Log.w(TAG, "createUserWithEmail:failure", task.getException());
                    Toast.makeText(Registro.this, "Authentication failed.",
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

}//fin del oncreate


//Metodos Propios
public boolean validarCampos(){
    try{
        String user = etUser.getText().toString();
        String correo = etEmail.getText().toString();
        String pass = etPass.getText().toString();
        if (user.isEmpty() || correo.isEmpty() || pass.isEmpty()){
            Toast.makeText(this, "Tiene campos en blanco", Toast.LENGTH_SHORT).show();
            return false;
        }else {
            return true;
        }
    }catch (Exception e){
        Toast.makeText(this, "Error al capturar los datos " + e.toString(), Toast.LENGTH_SHORT).show();
    }
    return false;
}

public void limpiarCampos(){
    etUser.setText("");
    etEmail.setText("");
    etPass.setText("");
}}

<LinearLayout
    android:id="@+id/lnlayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true"
    android:orientation="vertical">


    <TextView
        android:id="@+id/tv_logo"
        style="@style/tv_tituloStyle"
        android:layout_margin="50dp"
        android:text="@string/tv_logo" />

    <EditText
        android:id="@+id/et_userRegistro"
        style="@style/et_style"
        android:hint="@string/hint_userRegistro"
        android:inputType="textPersonName" />

    <EditText
        android:id="@+id/et_correoRegistro"
        style="@style/et_style"
        android:hint="@string/et_correoRegistro"
        android:inputType="textEmailAddress" />

    <EditText
        android:id="@+id/et_passwordRegistro"
        style="@style/et_style"
        android:hint="@string/hint_passRegistro"
        android:inputType="textPassword" />

    <Button
        android:id="@+id/bt_registro"
        style="@style/btn_style"
        android:text="@string/bt_registro" />


    <TextView
        android:id="@+id/tv_kris"
        style="@style/tv_style"
        android:text="@string/tv_kris" />


</LinearLayout>