Hello guys,

Thank you, Lance, for helping sort out this issue.  

I have updated the status of this item to "Declined" and raised the priority of the initial issue on UWP, so hopefully we'll manage to look into it soon.

Regards,
Yana
Progress Telerik

Hello Mehdi,

Thank you for the update with more details. 

The reason for the problem is still that same issue as you saw in the threads, but for a slightly different reason. In your case, you are loading the data too fast, before the native control is available, which is the root of the exception.

Solution

To solve this, do not use the page's OnAppearing. Instead, use the RadClaendar's NativeControlLoaded event to set the AppointmentSource.

This will give your app time to load the native component before attempting to start using it.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:telerikInput="clr-namespace:Telerik.XamarinForms.Input;assembly=Telerik.XamarinForms.Input"
             x:Class="XamarinAppUWP.MainPage">

    <telerikInput:RadCalendar NativeControlLoaded="MyCalendar_OnNativeControlLoaded"/>
</ContentPage>

using System;
using System.Collections.ObjectModel;
using Telerik.XamarinForms.Input;
using Xamarin.Forms;

namespace XamarinAppUWP
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void MyCalendar_OnNativeControlLoaded(object sender, EventArgs e)
        {
            var today = DateTime.Today;

            var items = new ObservableCollection<Appointment>
            {
                new Appointment { Color = Color.Green, Title = "T1", Detail = "D1", StartDate = today, EndDate = today.AddHours(2) },
                new Appointment { Color = Color.Red, Title = "T2", Detail = "D2", StartDate = today.AddDays(1), EndDate = today.AddDays(1).AddHours(2) },
                new Appointment { Color = Color.Blue, Title = "T3", Detail = "D3", StartDate = today.AddDays(2), EndDate = today.AddDays(2).AddHours(2) }
            };

            (sender as RadCalendar).AppointmentsSource = items;
        }
    }
}

Runtime

Notes

• For the purposes of this discussion, it doesn't matter if you're using our built-in Appointment or a custom IAppointment
• If you use any other View type, then the Calendar will wait to set the AppointmentSource until that view type has changed.

Demo

I have attached the updated demo. Please follow these steps to make sure you have properly unblocked the ZIP before extracting the files.

1. Download my attachment

2. Right-click on the ZIP file and select "Properties"

3. Select "Unblock" checkbox and then click "OK" (now you can unzip it)

4. Right-click on the ZIP file and select "Extract All"

5. Now you can open the sln in Visual Studio (I only kept the UWP project so it will load faster)

Unrelated

As to why you are having issues with Visual Studio is outside the control of our components. I'm not sure what the issue is there, I can confirm the sln and csproj files are correct. It may have been that you didnt unblock the ZIP, but I cant be sure without seeing the VS logs.

In any case, you should definitely make sure you're up to date on Visual Studio 2019. There have been some major changes with Xamarin that are required. Please run the Visual Studio Installer app (it is already on your machine) and make sure you're using at least v16.8.2.

Regards,
Lance | Manager Technical Support
Progress Telerik

Hi Mehdi,

I would need more details on the concrete setup, as I didn't manage to reproduce this issue on UWP with our latest releases.  I have attached my test project where the AppointmentsSource is set inside OnAppearing event, could you please download it and give it a try?  Can you modify it, so that it resembles your actual setup and send it back to me?

Thanks in advance

Regards,
Yana
Progress Telerik