How can i prevent a form from closing unless data is accepted by validation

Question

I try to use a custom-form in QGIS 3 to validate input-data before saving the data in a database. It would be nice to have the form open unless every input is correct. But the dialog/form closes even if the code detects wrong data...

...
my_dialog = None
inputField = None

def form_open(dialog, layerid, featureid):
    global my_dialog
    my_dialog=dialog

    global inputField
    inputField = my_dialog.findChild(QLineEdit,"qle_input")

    buttonBox = my_dialog.findChild(QDialogButtonBox,"buttonBox")

    buttonBox.accepted.disconnect()

    buttonBox.accepted.connect(validate)

    buttonBox.rejected.connect(my_dialog.resetValues)


def validate():
    inputString=inputField.text() # get text from qleInput
    pattern = re.compile("[^A-Za-z0-9]"); #pattern of not allowed data
    if re.findall(pattern,inputString): 
        #if match (wrong characters) - give a warning and let the dialog open to change text in qle_input
        textString='<b><center> Input contains wrong characters </center></b>'
        msgBox = QMessageBox()
        msgBox.setText(textString)
        msgBox.exec_()
    else: # Close dialog
        my_dialog.close

Answer 1

My solution (with some additonal adjustments to names) is:

from qgis.core import *
from qgis.gui import *
from PyQt5.QtWidgets import QLineEdit, QMessageBox, QDialogButtonBox
import re
from qgis.utils import iface

my_dialog = None
hausNr = None

def form_open(dialog, layerid, featureid):

    global my_dialog 
    my_dialog=dialog 
    global hausNr 
    hausNr = my_dialog.findChild(QLineEdit,"haus_nr") 
    hausNr.textChanged.connect(check_hausNr)

    global buttonBox
    buttonBox = my_dialog.findChild(QDialogButtonBox,"buttonBox")

def check_hausNr():
    buttonBox.button(buttonBox.Ok).setEnabled(False)
    hausNrText=hausNr.text()

    pattern = re.compile("[^A-Za-z0-9]");
    listWrongText=re.findall(pattern,hausNrText)
    warning="'"+", ".join(listWrongText)+"'"
    if listWrongText: 
        iface.messageBar().pushMessage("Wrong characters:", warning, level=Qgis.Critical, duration=3)
        hausNr.setStyleSheet("background-color: rgba(255, 150, 150, 100);")
        buttonBox.button(buttonBox.Ok).setEnabled(False)
    else:
        buttonBox.button(buttonBox.Ok).setEnabled(True)