Merge pull request #17 from umbraco-community/feature/our-fallback

Adds <our-fallback>

Author: Warren Buckley

Our.Umbraco.TagHelpers/OurFallbackTagHelper.cs

@@ -0,0 +1,70 @@
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Umbraco.Cms.Core.Models.PublishedContent;
+using Umbraco.Extensions;
+
+namespace Our.Umbraco.TagHelpers
+{
+    /// <summary>
+    /// Fallback Umbraco properties
+    /// </summary>
+    [HtmlTargetElement("our-fallback")]
+    public class OurFallbackTagHelper : TagHelper
+    {
+        /// <summary>
+        /// The property on the Model to use as a fallback such as Model.Header
+        /// Would just be Header
+        /// </summary>
+        [HtmlAttributeName("property")]
+        public ModelExpression ModelProperty { get; set; }
+
+        [HtmlAttributeName("mode")]
+        public Fallback Mode { get; set; }
+
+        /// <summary>
+        /// If using the fallback mode as Language then you can specify the culture to fallback to
+        /// </summary>
+        [HtmlAttributeName("culture")]
+        public string CultureCode { get; set; } = null;
+
+        [HtmlAttributeNotBound]
+        [ViewContext]
+        public ViewContext ViewContext { get; set; }
+
+        public override void Process(TagHelperContext context, TagHelperOutput output)
+        {
+            // Check to see that the Model Property is NOT a complex type or a collection of things
+            var isComplexType = ModelProperty.ModelExplorer.Metadata.IsComplexType;
+            var isEnumerableType = ModelProperty.ModelExplorer.Metadata.IsEnumerableType;
+
+            // Only can support simpler things such as strings (as if collection)
+            // We have no way of knowing how they want to iterate and display that HTML etc
+            if(isComplexType || isEnumerableType)
+            {
+                output.SuppressOutput();
+                return;
+            }
+
+            // Attempt to fetch/cast the Model as IPublishedContent
+            var contentNode = ViewContext.ViewData.Model as IPublishedContent;
+            if(contentNode == null)
+            {
+                output.SuppressOutput();
+                return;
+            }
+
+            output.TagName = ""; // Remove the outer <our-fallback>
+
+            // Get the Model property with fallback mode
+            var result = contentNode.Value(ModelProperty.Name, fallback: Mode, culture: CultureCode);
+
+            // If we have a value that can be
+            if (string.IsNullOrWhiteSpace($"{result}") == false)
+            {
+                output.Content.SetHtmlContent($"{result}");
+                return;
+            }
+        }
+    }
+}

README.md

@@ -187,6 +187,18 @@ It can be used in one of two ways, either by specifying the `src` attribute to a
 <our-svg media-item="@Model.Logo" />
 ```
 
+## `<our-fallback>`
+This tag helper element `<our-fallback>` uses the same fallback mode logic that is only available on the `Value()` method of the `IPublishedContent` interface that uses a string for the property name to lookup. In addition if the fallback value from a language or ancestors is not available we are still able to fallback to the content inside the tag.
+
+```cshtml
+@* Current way *@
+@Model.Value("Header", fallback:Fallback.ToLanguage)
+
+<h3><our-fallback property="Header" mode="Fallback.ToLanguage" culture="da-DK">I do NOT have a DK culture variant of this property</our-fallback></h3>
+<h3><our-fallback property="Header" mode="Fallback.ToAncestors">I do NOT have a Header property set on ANY parent and ancestors</our-fallback></h3> 
+```
+
+
 ## Video 📺
 [![How to create ASP.NET TagHelpers for Umbraco](https://user-images.githubusercontent.com/1389894/138666925-15475216-239f-439d-b989-c67995e5df71.png)](https://www.youtube.com/watch?v=3fkDs0NwIE8)