我需要检查用户输入的电话号码，该电话号码从0开始且长度至少为11。 我怎样才能做到这一点？ 这是我的代码：

<Entry x:Name="txtPhoneNumber" Placeholder="شماره تلفن" Margin="5,10,5" FlowDirection="RightToLeft"
                   MaxLength="11"
                   Keyboard="Telephone">
                <Entry.Behaviors>
                    <local:NumericValidationBehavior/>
                    <local:MaxLengthValidatorBehavior  MaxLength="11"/>
                </Entry.Behaviors>
            </Entry>

这里是NumericValidationBehavior类：

public class NumericValidationBehavior : Behavior<Entry>
{
    protected override void OnAttachedTo(Entry entry)
    {
        entry.TextChanged += OnEntryTextChanged;
        base.OnAttachedTo(entry);
    }
    protected override void OnDetachingFrom(Entry entry)
    {
        entry.TextChanged -= OnEntryTextChanged;
        base.OnDetachingFrom(entry);
    }
    private static void OnEntryTextChanged(object sender,TextChangedEventArgs args)
    {

        if (!string.IsnullOrWhiteSpace(args.NewTextvalue))
        {
            bool isValid = args.NewTextvalue.ToCharArray().All(x => char.IsDigit(x)); //Make sure all characters are numbers

            ((Entry)sender).Text = isValid ? args.NewTextvalue : args.NewTextvalue.Remove(args.NewTextvalue.Length - 1);
        }
    }
}