Hi Sulthan,Thank you for using Syncfusion Products.We have observed your query that you want to clear the items , before adding the items again in the MultiSelectionComboBox. In order to achieve your requirement , you need to use the same syntax as you mentioned Clear method of SelectedItems collection. But however, when we clear and add the items in MultiSelectionComboBox, we could face that the CheckBox in dropdown not get updated. Please find the screenshot for the same below:
Sample: https://www.syncfusion.com/downloads/support/forum/149515/ze/MultSelCombobox_modified-470600433So we have consider this behavior as a defect and logged the issue report on this. The patch for this fix is estimated to be available on 13th Dec 2019.You can track the status of this defect using the following feedback link:https://www.syncfusion.com/feedback/10493/selected-and-visual-items-are-not-updated-properly-in-multiselectioncomboboxRegardsVijayalakshmi V.R.