MainPage.xaml.cs

using YoutubeExplode;

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

        // The event handler for the download button
        private async void OnLoadClicked(object sender, EventArgs e)
        {
            // Getting the video url entry
            string enteredUrl = videoUrlEntry.Text;

            // Disabling the load button to prevent overuse
            loadButton.IsEnabled = false;

            // Checing if the entry is even a URL
            if (!Uri.TryCreate(enteredUrl, UriKind.Absolute, out _))
            {
                await DisplayAlert("Invalid URL", "Please enter a valid url", "OK");
                loadButton.IsEnabled = true;
                return;
            }

            // Event handler
            try
            {

                // Creating a new youtube client
                YoutubeClient youtubeClient = new YoutubeClient();

                // Getting the video object
                YoutubeExplode.Videos.Video video = await youtubeClient.Videos.GetAsync(enteredUrl);

                // Opening a new video page with the video object
                await Navigation.PushAsync(new VideoPage(video));
            }
            catch (YoutubeExplode.Exceptions.RequestLimitExceededException)
            {
                await DisplayAlert("Error", "You have exceeded the youtube rate limit. Possible causes:\n\n1) Using this app too much\n2) Using a VPN", "OK");
            }
            catch (System.Net.Http.HttpRequestException) 
            {
                await DisplayAlert("Error", "Please check your internet connection.", "OK");
            }catch (System.ArgumentException)
            {
                await DisplayAlert("Error", "Your entered URL was not a Youtube video.", "OK");
            }
            catch (Exception exception)
            {
                await DisplayAlert("Error", "We couldn't open the URL", "OK");
                Console.WriteLine(exception);
            }
            finally
            {
                // Resetting the load button
                loadButton.IsEnabled = true;
            }
        }
    }

}