ValidatorBuider

It was designed for a system that uses MVVM pattern that applies validation rules as the input is typed, offering feedback to the user as to whether or not these validation rules are met.

Validator

This class aims to apply all validation rules associated with a given key.

ValidatorBuilder

Allows build an instance of Validator through fluent design.

Example

Code snippet in a view model (MainWindowViewModel).

...

private readonly Validator Validator = ValidatorBuilder
    .Create()
        .RulesFor(Email, "Email requirements:")
            .Rule($"Must contain at least {EmailMinLength} characters.", x => x?.Length >= EmailMinLength)
            .Rule($"Must contain at most {EmailMaxLength} characters.", x => x?.Length <= EmailMaxLength)
            .Rule("The email must be in a valid format.", x => x is not null && new Regex(EmailPattern).Match(x).Success)

        .RulesFor(Password, "Password requirements:")
            .Rule($"Must be at least {PassMinLength} characters.", x => x?.Length >= PassMinLength)
            .Rule($"Must be at most {PassMaxLength} characters.", x => x?.Length <= PassMaxLength)
            .Rule("Must contain a number.", x => x is not null && x.ToCharArray().Any(c => char.IsNumber(c)))
            .Rule("Must contain a letter.", x => x is not null && x.ToCharArray().Any(c => char.IsLetter(c)))
            .Rule("Must contain a capital letter", x => x is not null && x.ToCharArray().Any(c => char.IsUpper(c)))
            .Rule("Must contain a symbol.", x => x is not null && x.IndexOfAny(new[] { '!', '@', '#', '%', '&', '*', '?' }) > -1)

        .RulesFor(reset, string.Empty)
    .Build();
    
...

public RuleGroup? RuleGroup { get => _ruleGroup; set => SetProperty(ref _ruleGroup, value); }

public string? Header { get => _header; set => SetProperty(ref _header, value); }

public string? PasswordBoxValue
{
    get => _passwordBoxValue;
    set
    {
        _ = SetProperty(ref _passwordBoxValue, value);

        RuleGroup = Validator.GetRulesFor(Password);
        Header = RuleGroup.Header;
        Validator.ValidateFor(Password, _passwordBoxValue);
    }
}

...

Code snipped in UI (MainWindow.xaml)

<Window.DataContext>
    <local:MainWindowViewModel />
</Window.DataContext>

...

<DataTemplate x:Key="ValidatorViewerItemTemplate">
    <StackPanel Orientation="Horizontal">
        <TextBlock
            x:Name="Glyph"
            VerticalAlignment="Bottom"
            FontFamily="Segoe MDL2 Assets"
            FontWeight="Bold"
            Foreground="Red"
            Text="&#xE894;  "
            TextWrapping="Wrap" />
        <TextBlock VerticalAlignment="Top" Text="{Binding Description}" />
    </StackPanel>
    <DataTemplate.Triggers>
        <DataTrigger Binding="{Binding IsValid}" Value="True">
            <Setter TargetName="Glyph" Property="Text" Value="&#xE73E;" />
            <Setter TargetName="Glyph" Property="TextBlock.Foreground" Value="Blue" />
            <Setter TargetName="Glyph" Property="Margin" Value="0,0,7,0" />
        </DataTrigger>
    </DataTemplate.Triggers>
</DataTemplate>

...

<PasswordBox
    x:Name="LoginPasswordBox"
    Height="Auto"
    Padding="2,2,2,2"
    d:Password="meupassword"
    Background="{x:Null}"
    BorderBrush="#FFCFCFC8"
    FontSize="14"
    Password=""
    PasswordChanged="LoginPasswordBox_PasswordChanged" />

<TextBlock
    x:Name="ValidationInfoTextBlock"
    Margin="0,20,0,10"
    FontSize="14"
    Text="{Binding Header}" />

<ItemsControl
    x:Name="ValidatorViewer"
    IsTabStop="False"
    ItemTemplate="{DynamicResource ValidatorViewerItemTemplate}"
    ItemsSource="{Binding RuleGroup.Rules}" />

...

Code snipped in UI (MainWindow.xaml.cs)

private void LoginPasswordBox_PasswordChanged(object sender, RoutedEventArgs e)
    => ((MainWindowViewModel)DataContext)
        .PasswordBoxValue = ((PasswordBox)sender).Password;

Validation rules are executed with each keystroke and the validator displays whether the rule was met or not.