.Net MAUIのコントロールをハンドラーでカスタマイズする方法について

#if ANDROID

using AndroidX.AppCompat.Widget;

#endif

using Microsoft.Maui.Handlers;

// 名前空間はプロジェクトに合わせてください。
namespace SampleApp;

public partial class App : Application
{
    public App()
    {
        InitializeComponent();
    }

    protected override Window CreateWindow(IActivationState? activationState)
    {
        EntryHandler.Mapper.AppendToMapping("CustomEntry", (handler, view) =>
        {
            if (view is not Entry entry) return;
            SetBackgroundColor(entry.Text);

#if WINDOWS
            handler.PlatformView.TextChanging += (sender, e) =>
            {
                SetBackgroundColor(sender.Text);
            };
#elif ANDROID
            handler.PlatformView.TextChanged += (sender, e) =>
            {
                SetBackgroundColor((sender as AppCompatEditText)?.Text);
            };
#endif
            void SetBackgroundColor(string? text)
            {
                if (string.IsNullOrEmpty(text))
                {
                    entry.BackgroundColor = new Color(255, 150, 150);
                }
                else
                {
                    entry.BackgroundColor = new Color(255, 255, 255);
                    entry.TextColor = new Color(30, 30, 30);
                }
            }
        });

        return new Window(new AppShell());
    }
}

<Entry
    HandlerChanging="Entry_HandlerChanging"
    HandlerChanged="Entry_HandlerChanged" />

#if WINDOWS

using Microsoft.UI.Xaml.Controls;

#elif ANDROID

using AndroidX.AppCompat.Widget;
using Microsoft.Maui.Controls.Platform;

#endif

using Microsoft.Maui.Handlers;
using Microsoft.Maui.Platform;

// 名前空間はプロジェクトに合わせてください。
namespace SampleApp;

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

    private void Entry_HandlerChanging(object sender, HandlerChangingEventArgs e)
    {
#if WINDOWS

        if (e.OldHandler?.PlatformView is TextBox textBox)
        {
            textBox.TextChanging -= TextBox_TextChanging;
        }

#elif ANDROID

        if (e.OldHandler?.PlatformView is AppCompatEditText editText)
        {
            editText.TextChanged -= EditText_TextChanged;
        }

#endif
    }

    private void Entry_HandlerChanged(object sender, EventArgs e)
    {
        if (sender is not Entry entry) return;
#if WINDOWS

        if (entry.Handler?.PlatformView is TextBox textBox)
        {
            textBox.Background = new Color(255, 150, 150).ToPlatform();
            textBox.TextChanging += TextBox_TextChanging;
        }

#elif ANDROID

        if (entry.Handler?.PlatformView is AppCompatEditText editText)
        {
            editText.UpdateBackground(new Color(255, 150, 150));
            editText.TextChanged += EditText_TextChanged;
        }
#endif
    }

#if WINDOWS

    private void TextBox_TextChanging(TextBox sender, TextBoxTextChangingEventArgs args)
    {
        if (string.IsNullOrEmpty(sender.Text))
        {
            sender.Background = new Color(255, 150, 150).ToPlatform();
        }
        else
        {
            sender.Background = new Color(255, 255, 255).ToPlatform();
            sender.Foreground = new Color(30, 30, 30).ToPlatform();
        }
    }

#elif ANDROID

    private void EditText_TextChanged(object? sender, Android.Text.TextChangedEventArgs e)
    {
        if (sender is AppCompatEditText editText)
        {
            if (string.IsNullOrEmpty(editText.Text))
            {
                editText.UpdateBackground(new Color(255, 150, 150));
            }
            else
            {
                editText.UpdateBackground(new Color(255, 255, 255));
                editText.UpdateTextColor(new Color(30, 30, 30));
            }
        }
    }

#endif
}