benmccallum
commented
3 months ago A drop-in solution for anyone who wants this right now.
using Microsoft.AspNetCore.Razor.TagHelpers;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
// May be absorbed into the core library if this issue is approved
// https://github.com/microsoft/FeatureManagement-Dotnet/issues/483
namespace Microsoft.FeatureManagement.Mvc.TagHelpers
{
/// <summary>
/// Provides an attribute-based tag helper that can be used to conditionally render content based on a feature's state.
/// </summary>
[HtmlTargetElement(Attributes = "feat-name")]
public class FeatTagHelper : TagHelper
{
private readonly IFeatureManager _featureManager;
/// <summary>
/// A feature name, or comma separated list of feature names, for which the content should be rendered. By default, all specified features must be enabled to render the content, but this requirement can be controlled by the <see cref="Requirement"/> property.
/// </summary>
public string FeatName { get; set; } = "";
/// <summary>
/// Controls whether 'All' or 'Any' feature in a list of features should be enabled to render the content within the feature tag.
/// </summary>
public RequirementType FeatRequirement { get; set; } = RequirementType.All;
/// <summary>
/// Negates the evaluation for whether or not a feature tag should display content. This is used to display alternate content when a feature or set of features are disabled.
/// </summary>
public bool FeatNegate { get; set; }
/// <summary>
/// Creates a feature tag helper.
/// </summary>
/// <param name="featureManager">The feature manager snapshot to use to evaluate feature state.</param>
public FeatTagHelper(IFeatureManagerSnapshot featureManager)
{
_featureManager = featureManager;
}
/// <summary>
/// Processes the tag helper context to evaluate if the feature's content should be rendered.
/// </summary>
/// <param name="context">The tag helper context.</param>
/// <param name="output">The tag helper output.</param>
public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
{
if (output.TagName == "feature")
{
// We don't want the feature element to actually be a part of HTML, so we strip it
output.TagName = null;
}
bool enabled = false;
if (!string.IsNullOrEmpty(FeatName))
{
IEnumerable<string> names = FeatName.Split(',').Select(n => n.Trim());
enabled = FeatRequirement == RequirementType.All
? await All(names, _featureManager.IsEnabledAsync)
: await Any(names, _featureManager.IsEnabledAsync);
}
if (FeatNegate)
{
enabled = !enabled;
}
if (!enabled)
{
output.SuppressOutput();
}
}
#pragma warning disable IDE1006
#pragma warning disable IDE0007
#pragma warning disable VSTHRD200
private static async Task<bool> Any<TSource>(IEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
{
bool enabled = false;
foreach (TSource item in source)
{
if (await predicate(item).ConfigureAwait(false))
{
enabled = true;
break;
}
}
return enabled;
}
private static async Task<bool> All<TSource>(IEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
{
bool enabled = true;
foreach (TSource item in source)
{
if (!await predicate(item).ConfigureAwait(false))
{
enabled = false;
break;
}
}
return enabled;
}
}
}
zhiyuanliang-ms
I think this would be extremely straightforward to implement and make for a tidier, less disruptive use of the tag helper.
Required changes:
FeatureTagHelperintoFeatTagHelper(orFeatureAttributeTagHelper)[HtmlTargetElement(Attributes = nameof(FeatName))]Featoutput.TagName = null;so the existing HTML element stays in placeoutput.TagName = null;can be run ifoutput.TagName == "feature"It's really quite similar to the
ConditionTagHelperin the docs here.I'm happy to implement this as a PR if it will be accepted. I'll probably be creating one in our repo in the short term.