Merge branch 'master' of https://git.wyant.us/jaime/531Calculator

531Calculator/Components/MyValidationMessage.cs

@@ -0,0 +1,106 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Forms;
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace FiveThreeOneCalculator.Components
+{
+    /// <summary>
+    /// Displays a list of validation messages for a specified field within a cascaded <see cref="EditContext"/>.
+    /// </summary>
+    public class MyValidationMessage<TValue> : ComponentBase, IDisposable
+    {
+        private EditContext? _previousEditContext;
+        private Expression<Func<TValue>>? _previousFieldAccessor;
+        private readonly EventHandler<ValidationStateChangedEventArgs>? _validationStateChangedHandler;
+        private FieldIdentifier _fieldIdentifier;
+
+        /// <summary>
+        /// Gets or sets a collection of additional attributes that will be applied to the created <c>div</c> element.
+        /// </summary>
+        [Parameter(CaptureUnmatchedValues = true)] public IReadOnlyDictionary<string, object>? AdditionalAttributes { get; set; }
+
+        [CascadingParameter] EditContext CurrentEditContext { get; set; } = default!;
+
+        /// <summary>
+        /// Specifies the field for which validation messages should be displayed.
+        /// </summary>
+        [Parameter] public Expression<Func<TValue>>? For { get; set; }
+
+        /// <summary>`
+        /// Constructs an instance of <see cref="ValidationMessage{TValue}"/>.
+        /// </summary>
+        public MyValidationMessage()
+        {
+            _validationStateChangedHandler = (sender, eventArgs) => StateHasChanged();
+        }
+
+        /// <inheritdoc />
+        protected override void OnParametersSet()
+        {
+            if (CurrentEditContext == null)
+            {
+                throw new InvalidOperationException($"{GetType()} requires a cascading parameter " +
+                    $"of type {nameof(EditContext)}. For example, you can use {GetType()} inside " +
+                    $"an {nameof(EditForm)}.");
+            }
+
+            if (For == null) // Not possible except if you manually specify T
+            {
+                throw new InvalidOperationException($"{GetType()} requires a value for the " +
+                    $"{nameof(For)} parameter.");
+            }
+            else if (For != _previousFieldAccessor)
+            {
+                _fieldIdentifier = FieldIdentifier.Create(For);
+                _previousFieldAccessor = For;
+            }
+
+            if (CurrentEditContext != _previousEditContext)
+            {
+                DetachValidationStateChangedListener();
+                CurrentEditContext.OnValidationStateChanged += _validationStateChangedHandler;
+                _previousEditContext = CurrentEditContext;
+            }
+        }
+
+        /// <inheritdoc />
+        protected override void BuildRenderTree(RenderTreeBuilder builder)
+        {
+            var l = CurrentEditContext.GetValidationMessages().ToArray();
+            foreach (var message in CurrentEditContext.GetValidationMessages(_fieldIdentifier))
+            {
+                builder.OpenElement(0, "div");
+                builder.AddMultipleAttributes(1, AdditionalAttributes);
+                builder.AddAttribute(2, "class", "validation-message");
+                builder.AddContent(3, message);
+                builder.CloseElement();
+            }
+        }
+
+        /// <summary>
+        /// Called to dispose this instance.
+        /// </summary>
+        /// <param name="disposing"><see langword="true"/> if called within <see cref="IDisposable.Dispose"/>.</param>
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        void IDisposable.Dispose()
+        {
+            DetachValidationStateChangedListener();
+            Dispose(disposing: true);
+        }
+
+        private void DetachValidationStateChangedListener()
+        {
+            if (_previousEditContext != null)
+            {
+                _previousEditContext.OnValidationStateChanged -= _validationStateChangedHandler;
+            }
+        }
+    }
+}