Для Xamarin.Forms для этого можно использовать IValidationRule.
Во-первых, создание класса, производного от интерфейса IValidationRule, для указания правил проверки.
public interface IValidationRule<T>
{
string ValidationMessage { get; set; }
bool Check(T value);
}
public class IsNotNullOrEmptyRule<T> : IValidationRule<T>
{
public string ValidationMessage { get; set; }
public bool Check(T value)
{
if (value == null)
{
return false;
}
var str = $"{value }";
return !string.IsNullOrWhiteSpace(str);
}
}
public class HasValidAgeRule<T> : IValidationRule<T>
{
public string ValidationMessage { get; set; }
public bool Check(T value)
{
if (value is DateTime bday)
{
DateTime today = DateTime.Today;
int age = today.Year - bday.Year;
return (age >= 18);
}
return false;
}
}
Во-вторых, добавление правил проверки к свойству.
public interface IValidatable<T> : INotifyPropertyChanged
{
List<IValidationRule<T>> Validations { get; }
List<string> Errors { get; set; }
bool Validate();
bool IsValid { get; set; }
}
public class ValidatableObject<T> : IValidatable<T>
{
public event PropertyChangedEventHandler PropertyChanged;
public List<IValidationRule<T>> Validations { get; } = new List<IValidationRule<T>>();
public List<string> Errors { get; set; } = new List<string>();
public bool CleanOnChange { get; set; } = true;
T _value;
public T Value
{
get => _value;
set
{
_value = value;
if (CleanOnChange)
IsValid = true;
}
}
public bool IsValid { get; set; } = true;
public virtual bool Validate()
{
Errors.Clear();
IEnumerable<string> errors = Validations.Where(v => !v.Check(Value))
.Select(v => v.ValidationMessage);
Errors = errors.ToList();
IsValid = !Errors.Any();
return this.IsValid;
}
public override string ToString()
{
return $"{Value}";
}
}
public class validationmodel: INotifyPropertyChanged
{
public ValidatableObject<string> FirstName { get; set; } = new ValidatableObject<string>();
public ValidatableObject<string> LastName { get; set; } = new ValidatableObject<string>();
public ValidatableObject<DateTime> BirthDay { get; set; } = new ValidatableObject<DateTime>() { Value = DateTime.Now };
public validationmodel()
{
FirstName.Value = null;
AddValidationRules();
AreFieldsValid();
}
public event PropertyChangedEventHandler PropertyChanged;
public void AddValidationRules()
{
FirstName.Validations.Add(new IsNotNullOrEmptyRule<string> { ValidationMessage = "First Name Required" });
LastName.Validations.Add(new IsNotNullOrEmptyRule<string> { ValidationMessage = "Last Name Required" });
BirthDay.Validations.Add(new HasValidAgeRule<DateTime> { ValidationMessage = "You must be 18 years of age or older" });
}
bool AreFieldsValid()
{
bool isFirstNameValid = FirstName.Validate();
bool isLastNameValid = LastName.Validate();
bool isBirthDayValid = BirthDay.Validate();
return isFirstNameValid && isLastNameValid && isBirthDayValid;
}
}
Выделение элемента управления, содержащего недопустимые данные:
public class FirstValidationErrorConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
ICollection<string> errors = value as ICollection<string>;
return errors != null && errors.Count > 0 ? errors.ElementAt(0) : null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
public class InverseBoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is bool))
{
throw new InvalidOperationException("The target must be a boolean");
}
return !(bool)value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
}
public class BehaviorBase<T> : Behavior<T>
where T : BindableObject
{
#region Properties
public T AssociatedObject
{
get;
private set;
}
#endregion
#region NormalMethods
private void OnBindingContextChanged(object sender, EventArgs e)
{
OnBindingContextChanged();
}
#endregion
#region Overrides
protected override void OnAttachedTo(T bindable)
{
base.OnAttachedTo(bindable);
AssociatedObject = bindable;
if (bindable.BindingContext != null)
{
BindingContext = bindable.BindingContext;
}
bindable.BindingContextChanged += OnBindingContextChanged;
}
protected override void OnDetachingFrom(T bindable)
{
base.OnDetachingFrom(bindable);
bindable.BindingContextChanged -= OnBindingContextChanged;
AssociatedObject = null;
}
protected override void OnBindingContextChanged()
{
base.OnBindingContextChanged();
BindingContext = AssociatedObject.BindingContext;
}
#endregion
}
public class EntryLineValidationBehaviour : BehaviorBase<Entry>
{
#region StaticFields
public static readonly BindableProperty IsValidProperty = BindableProperty.Create(nameof(IsValid), typeof(bool), typeof(EntryLineValidationBehaviour), true, BindingMode.Default, null, (bindable, oldValue, newValue) => OnIsValidChanged(bindable, newValue));
#endregion
#region Properties
public bool IsValid
{
get
{
return (bool)GetValue(IsValidProperty);
}
set
{
SetValue(IsValidProperty, value);
}
}
#endregion
#region StaticMethods
private static void OnIsValidChanged(BindableObject bindable, object newValue)
{
if (bindable is EntryLineValidationBehaviour IsValidBehavior &&
newValue is bool IsValid)
{
IsValidBehavior.AssociatedObject.PlaceholderColor = IsValid ? Color.Default : Color.Red;
}
}
#endregion
}
Главная страница.xaml:
<ContentPage
x:Class="validationapp.MainPage"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:behaviour="clr-namespace:validationapp.Behaviors"
xmlns:converter="clr-namespace:validationapp.converters"
xmlns:local="clr-namespace:validationapp">
<ContentPage.Resources>
<converter:InverseBoolConverter x:Key="InverseBoolConverter" />
<converter:FirstValidationErrorConverter x:Key="FirstValidationErrorConverter" />
<Style x:Key="ErrorTextStyle" TargetType="Label">
<Setter Property="TextColor" Value="Red" />
<Setter Property="FontSize" Value="12" />
</Style>
</ContentPage.Resources>
<StackLayout>
<!-- First Name -->
<Entry Placeholder="First Name" Text="{Binding FirstName.Value}">
<Entry.Behaviors>
<behaviour:EntryLineValidationBehaviour IsValid="{Binding FirstName.IsValid}" />
</Entry.Behaviors>
</Entry>
<Label
IsVisible="{Binding FirstName.IsValid, Converter={StaticResource InverseBoolConverter}}"
Style="{StaticResource ErrorTextStyle}"
Text="{Binding FirstName.Errors, Converter={StaticResource FirstValidationErrorConverter}}" />
<!-- /First Name -->
<!-- Last Name -->
<Entry Placeholder="Last Name" Text="{Binding LastName.Value}">
<Entry.Behaviors>
<behaviour:EntryLineValidationBehaviour IsValid="{Binding LastName.IsValid}" />
</Entry.Behaviors>
</Entry>
<Label
IsVisible="{Binding LastName.IsValid, Converter={StaticResource InverseBoolConverter}}"
Style="{StaticResource ErrorTextStyle}"
Text="{Binding LastName.Errors, Converter={StaticResource FirstValidationErrorConverter}}" />
<!-- /Last Name -->
<!-- Birthday -->
<DatePicker Date="{Binding BirthDay.Value}" />
<Label
IsVisible="{Binding BirthDay.IsValid, Converter={StaticResource InverseBoolConverter}}"
Style="{StaticResource ErrorTextStyle}"
Text="{Binding BirthDay.Errors, Converter={StaticResource FirstValidationErrorConverter}}" />
<!-- Birthday -->
</StackLayout>
Вы также можете запускать проверку при изменении свойств для команды Entry.
Более подробную информацию о валидации см.:
https://docs.microsoft.com/en-us/xamarin/xamarin-forms/enterprise-application-patterns/validation
person
Cherry Bu - MSFT
schedule
10.12.2020
