Last Updated: 21 Dec 2023 13:19 by ADMIN
Release 6.6.0
Created on: 20 Nov 2023 08:33
Category: ComboBox
Type: Bug Report
ComboBox: [MacCatalyst] InvalidOperationException when trying to open the dropdown in ListView or CollectionView
If a RadComboBox is used as an ItemTemplate for a ListView or CollectionView on MacCatalyst, the application crashes every time you attempt to open the dropdown with the following exception:

System.InvalidOperationException: Event registration is overwriting existing delegate. Either just use events or your own delegate: Microsoft.Maui.Controls.Handlers.Items.ReorderableItemsViewDelegator`2[Microsoft.Maui.Controls.ReorderableItemsView,Microsoft.Maui.Controls.Handlers.Items.ReorderableItemsViewController`1[Microsoft.Maui.Controls.ReorderableItemsView]] UIKit.UIScrollView+_UIScrollViewDelegate
   at UIKit.UIApplication.EnsureEventAndDelegateAreNotMismatched(Object del, Type expectedType)
   at UIKit.UIScrollView.EnsureUIScrollViewDelegate()
   at UIKit.UIScrollView.add_Scrolled(EventHandler value)
   at Telerik.Maui.Controls.RadPopup.SetPopupIsOpen(Boolean value)
   at Telerik.Maui.Controls.RadPopup.UpdatePopup()
1 comment
Posted on: 20 Nov 2023 08:43


Inside the AppDelegate.cs file set the CheckForEventAndDelegateMismatches to false:

using Foundation;
using UIKit;
namespace TelerikComboboxBug;

public class AppDelegate : MauiUIApplicationDelegate
    protected override MauiApp CreateMauiApp() {
        UIApplication.CheckForEventAndDelegateMismatches = false;
        return MauiProgram.CreateMauiApp();

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