If there is both an attribute validate_before_accept=True and a method validate() in the config_widget then calll validate() when the config dialog OK button is pressed.

src/calibre/customize/__init__.py

@@ -149,17 +149,35 @@ class Plugin:  # {{{
 
         from calibre.gui2 import gprefs
 
+        class ConfigDialog(QDialog):
+
+            def __init__(self, parent, config_widget):
+                super().__init__(parent)
+                self.config_widget = config_widget
+
+            def accept(self):
+                print('in accept')
+                if ((validate := getattr(self.config_widget, 'validate', None)) and
+                        getattr(self.config_widget, 'validate_before_accept', False)):
+                    print('have validate and validate_before_accept')
+                    if not validate():
+                        return
+                print('accepting')
+                super().accept()
+
+        try:
+            config_widget = self.config_widget()
+        except NotImplementedError:
+            config_widget = None
+
         prefname = 'plugin config dialog:'+self.type + ':' + self.name
-        config_dialog = QDialog(parent)
+
+        config_dialog = ConfigDialog(parent, config_widget)
         button_box = QDialogButtonBox(QDialogButtonBox.StandardButton.Ok | QDialogButtonBox.StandardButton.Cancel)
         v = QVBoxLayout(config_dialog)
         button_box.accepted.connect(config_dialog.accept)
         button_box.rejected.connect(config_dialog.reject)
         config_dialog.setWindowTitle(_('Customize') + ' ' + self.name)
-        try:
-            config_widget = self.config_widget()
-        except NotImplementedError:
-            config_widget = None
 
         if isinstance(config_widget, tuple):
             from calibre.gui2 import warning_dialog

src/calibre/devices/kobo/kobotouch_config.py

@@ -54,11 +54,13 @@ class KOBOTOUCHConfig(TabbedDeviceConfig):
 
     def __init__(self, device_settings, all_formats, supports_subdirs,
                     must_read_metadata, supports_use_author_sort,
-                    extra_customization_message, device, extra_customization_choices=None, parent=None):
+                    extra_customization_message, device, extra_customization_choices=None,
+                    parent=None):
 
         super().__init__(device_settings, all_formats, supports_subdirs,
                     must_read_metadata, supports_use_author_sort,
-                    extra_customization_message, device, extra_customization_choices, parent)
+                    extra_customization_message, device, extra_customization_choices, parent,
+                    validate_before_accept=True)
 
         self.device_settings = device_settings
         self.all_formats = all_formats
@@ -570,7 +572,6 @@ class CollectionsGroupBox(DeviceOptionsGroupBox):
         self.use_collections_template_checkbox.clicked.connect(self.use_collections_template_checkbox_clicked)
         self.use_collections_columns_checkbox_clicked(device.get_pref('use_collections_columns'))
         self.use_collections_template_checkbox_clicked(device.get_pref('use_collections_template'))
-        self.collections_columns_edit.editingFinished.connect(self.validate_collections_columns)
 
     def validate(self):
         v = self.validate_collections_columns()
@@ -590,7 +591,6 @@ class CollectionsGroupBox(DeviceOptionsGroupBox):
             error_dialog(self, _('Kobo configuration: Invalid collection column names'),
                 '<p>'+_("Collection column names that don't exist in the library: {0}").format(s),
                 show=True)
-            self.collections_columns_edit.setFocus(Qt.FocusReason.OtherFocusReason)
             return False
         return True
 

src/calibre/gui2/device_drivers/tabbed_device_config.py

@@ -63,15 +63,19 @@ class TabbedDeviceConfig(QTabWidget):
     DeviceConfigTab, for each set of options. Within the tabs, group boxes, subclassed
     from DeviceOptionsGroupBox, are created to further group the options. The group
     boxes can be coded to support any control type and dependencies between them.
+
+    Set validate_before_accept to True if you want validation() to be called
+    when OK is pressed
     '''
 
     def __init__(self, device_settings, all_formats, supports_subdirs,
                     must_read_metadata, supports_use_author_sort,
                     extra_customization_message, device,
-                    extra_customization_choices=None, parent=None):
+                    extra_customization_choices=None, parent=None, validate_before_accept = False):
         QTabWidget.__init__(self, parent)
         self._device = weakref.ref(device)
 
+        self.validate_before_accept = validate_before_accept
         self.device_settings = device_settings
         self.all_formats = set(all_formats)
         self.supports_subdirs = supports_subdirs