如何在keyborard Xamarin.forms中只输入英文数字

using Xamarin.Forms;

public class CustomEntry : Entry
{
    public CustomEntry()
    {
        // 使用正则表达式限制只能输入英文和数字
        this.TextChanged += (sender, e) =>
        {
            var entry = (Entry)sender;
            var newText = Regex.Replace(entry.Text, "[^a-zA-Z0-9]", "");
            if (newText != entry.Text)
            {
                entry.Text = newText;
            }
        };
    }
}

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:YourNamespace"
             x:Class="YourNamespace.YourPage">
    <StackLayout>
        <local:CustomEntry Placeholder="Enter text" />
    </StackLayout>
</ContentPage>