qt dialogs: disconnect signals and unregister callbacks in closeEvent

electrum/gui/qt/channel_details.py

@@ -224,3 +224,7 @@ class ChannelDetailsDialog(QtWidgets.QDialog, MessageBoxMixin, QtEventListener):
         vbox.addLayout(Buttons(CloseButton(self)))
         # initialize sent/received fields
         self.update()
+
+    def closeEvent(self, event):
+        self.unregister_callbacks()
+        event.accept()

electrum/gui/qt/settings_dialog.py

@@ -580,3 +580,11 @@ class SettingsDialog(QDialog, QtEventListener):
         self.config.set_key('alias', alias, True)
         if alias:
             self.wallet.contacts.fetch_openalias(self.config)
+
+    def closeEvent(self, event):
+        self.unregister_callbacks()
+        try:
+            self.app.alias_received_signal.disconnect(self.set_alias_color)
+        except TypeError:
+            pass  # 'method' object is not connected
+        event.accept()