ValidationBehavior: Added IsNotValid property

samples/XCT.Sample/Pages/Behaviors/EmailValidationBehaviorPage.xaml

@@ -15,11 +15,21 @@
                  Spacing="50"
                  VerticalOptions="CenterAndExpand">
         <Label Text="Text color will change accordingly to the style that is configured when a invalid value (email address) is entered." />
-        <Entry Placeholder="Email">
-            <Entry.Behaviors>
-                <xct:EmailValidationBehavior DecorationFlags="Trim" InvalidStyle="{StaticResource InvalidEntryStyle}"/>
-            </Entry.Behaviors>
-        </Entry>
+        <StackLayout Spacing="3">
+            <Entry Placeholder="Email">
+                <Entry.Behaviors>
+                    <xct:EmailValidationBehavior
+                        x:Name="EmailValidator"
+                        DecorationFlags="Trim"
+                        InvalidStyle="{StaticResource InvalidEntryStyle}"/>
+                </Entry.Behaviors>
+            </Entry>
+            <Label Text="Invalid email"
+                   TextColor="Red"
+                   FontSize="10"
+                   IsVisible="{Binding IsNotValid, Source={x:Reference EmailValidator}}"
+                   />
+        </StackLayout>
     </StackLayout>
 
 </pages:BasePage>

src/CommunityToolkit/Xamarin.CommunityToolkit/Behaviors/Validators/MultiValidationBehavior.shared.cs

@@ -43,7 +43,7 @@ protected override bool Validate(object value)
 			{
 				c.Value = value;
 				c.ForceValidate();
-				return !c.IsValid;
+				return c.IsNotValid;
 			}).Select(c => GetError(c));
 
 			if (!errors.Any())

src/CommunityToolkit/Xamarin.CommunityToolkit/Behaviors/Validators/ValidationBehavior.shared.cs

@@ -6,8 +6,11 @@ namespace Xamarin.CommunityToolkit.Behaviors.Internals
 {
 	public abstract class ValidationBehavior : BaseBehavior<VisualElement>
 	{
+		public static readonly BindableProperty IsNotValidProperty =
+			BindableProperty.Create(nameof(IsNotValid), typeof(bool), typeof(ValidationBehavior), false, BindingMode.OneWayToSource);
+
 		public static readonly BindableProperty IsValidProperty =
-			BindableProperty.Create(nameof(IsValid), typeof(bool), typeof(ValidationBehavior), true, BindingMode.OneWayToSource);
+			BindableProperty.Create(nameof(IsValid), typeof(bool), typeof(ValidationBehavior), true, BindingMode.OneWayToSource, propertyChanged: OnIsValidPropertyChanged);
 
 		public static readonly BindableProperty ValidStyleProperty =
 			BindableProperty.Create(nameof(ValidStyle), typeof(Style), typeof(ValidationBehavior), propertyChanged: OnValidationPropertyChanged);
@@ -39,6 +42,12 @@ public bool IsValid
 			set => SetValue(IsValidProperty, value);
 		}
 
+		public bool IsNotValid
+		{
+			get => (bool)GetValue(IsNotValidProperty);
+			set => SetValue(IsNotValidProperty, value);
+		}
+
 		public Style ValidStyle
 		{
 			get => (Style)GetValue(ValidStyleProperty);
@@ -124,6 +133,9 @@ protected override void OnViewPropertyChanged(object sender, PropertyChangedEven
 		protected static void OnValidationPropertyChanged(BindableObject bindable, object oldValue, object newValue)
 			=> ((ValidationBehavior)bindable).UpdateState(false);
 
+		static void OnIsValidPropertyChanged(BindableObject bindable, object oldValue, object newValue)
+			=> ((ValidationBehavior)bindable).OnIsValidPropertyChanged();
+
 		static void OnValuePropertyChanged(BindableObject bindable, object oldValue, object newValue)
 		{
 			((ValidationBehavior)bindable).OnValuePropertyChanged();
@@ -139,6 +151,9 @@ static object GetDefaultForceValidateCommand(BindableObject bindable)
 		static object GetDefaultValuePropertyName(BindableObject bindable)
 			=> ((ValidationBehavior)bindable).DefaultValuePropertyName;
 
+		void OnIsValidPropertyChanged()
+			=> IsNotValid = !IsValid;
+
 		void OnValuePropertyChanged()
 		{
 			if (isAttaching)