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NavLink.cs
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NavLink.cs
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// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Components.Rendering;
namespace Microsoft.AspNetCore.Components.Routing
{
/// <summary>
/// A component that renders an anchor tag, automatically toggling its 'active'
/// class based on whether its 'href' matches the current URI.
/// </summary>
public class NavLink : ComponentBase, IDisposable
{
private const string DefaultActiveClass = "active";
private bool _isActive;
private string _hrefAbsolute;
private string _class;
/// <summary>
/// Gets or sets the CSS class name applied to the NavLink when the
/// current route matches the NavLink href.
/// </summary>
[Parameter]
public string ActiveClass { get; set; }
/// <summary>
/// Gets or sets a collection of additional attributes that will be added to the generated
/// <c>a</c> element.
/// </summary>
[Parameter(CaptureUnmatchedValues = true)]
public IReadOnlyDictionary<string, object> AdditionalAttributes { get; set; }
/// <summary>
/// Gets or sets the computed CSS class based on whether or not the link is active.
/// </summary>
protected string CssClass { get; set; }
/// <summary>
/// Gets or sets the child content of the component.
/// </summary>
[Parameter]
public RenderFragment ChildContent { get; set; }
/// <summary>
/// Gets or sets a value representing the URL matching behavior.
/// </summary>
[Parameter]
public NavLinkMatch Match { get; set; }
[Inject] private NavigationManager NavigationManger { get; set; }
/// <inheritdoc />
protected override void OnInitialized()
{
// We'll consider re-rendering on each location change
NavigationManger.LocationChanged += OnLocationChanged;
}
/// <inheritdoc />
protected override void OnParametersSet()
{
// Update computed state
var href = (string)null;
if (AdditionalAttributes != null && AdditionalAttributes.TryGetValue("href", out var obj))
{
href = Convert.ToString(obj);
}
_hrefAbsolute = href == null ? null : NavigationManger.ToAbsoluteUri(href).AbsoluteUri;
_isActive = ShouldMatch(NavigationManger.Uri);
_class = (string)null;
if (AdditionalAttributes != null && AdditionalAttributes.TryGetValue("class", out obj))
{
_class = Convert.ToString(obj);
}
UpdateCssClass();
}
/// <inheritdoc />
public void Dispose()
{
// To avoid leaking memory, it's important to detach any event handlers in Dispose()
NavigationManger.LocationChanged -= OnLocationChanged;
}
private void UpdateCssClass()
{
CssClass = _isActive ? CombineWithSpace(_class, ActiveClass ?? DefaultActiveClass) : _class;
}
private void OnLocationChanged(object sender, LocationChangedEventArgs args)
{
// We could just re-render always, but for this component we know the
// only relevant state change is to the _isActive property.
var shouldBeActiveNow = ShouldMatch(args.Location);
if (shouldBeActiveNow != _isActive)
{
_isActive = shouldBeActiveNow;
UpdateCssClass();
StateHasChanged();
}
}
private bool ShouldMatch(string currentUriAbsolute)
{
if (EqualsHrefExactlyOrIfTrailingSlashAdded(currentUriAbsolute))
{
return true;
}
if (Match == NavLinkMatch.Prefix
&& IsStrictlyPrefixWithSeparator(currentUriAbsolute, _hrefAbsolute))
{
return true;
}
return false;
}
private bool EqualsHrefExactlyOrIfTrailingSlashAdded(string currentUriAbsolute)
{
if (string.Equals(currentUriAbsolute, _hrefAbsolute, StringComparison.Ordinal))
{
return true;
}
if (currentUriAbsolute.Length == _hrefAbsolute.Length - 1)
{
// Special case: highlight links to http://host/path/ even if you're
// at http://host/path (with no trailing slash)
//
// This is because the router accepts an absolute URI value of "same
// as base URI but without trailing slash" as equivalent to "base URI",
// which in turn is because it's common for servers to return the same page
// for http://host/vdir as they do for host://host/vdir/ as it's no
// good to display a blank page in that case.
if (_hrefAbsolute[_hrefAbsolute.Length - 1] == '/'
&& _hrefAbsolute.StartsWith(currentUriAbsolute, StringComparison.Ordinal))
{
return true;
}
}
return false;
}
protected override void BuildRenderTree(RenderTreeBuilder builder)
{
builder.OpenElement(0, "a");
builder.AddMultipleAttributes(1, AdditionalAttributes);
builder.AddAttribute(2, "class", CssClass);
builder.AddContent(3, ChildContent);
builder.CloseElement();
}
private string CombineWithSpace(string str1, string str2)
=> str1 == null ? str2
: (str2 == null ? str1 : $"{str1} {str2}");
private static bool IsStrictlyPrefixWithSeparator(string value, string prefix)
{
var prefixLength = prefix.Length;
if (value.Length > prefixLength)
{
return value.StartsWith(prefix, StringComparison.Ordinal)
&& (
// Only match when there's a separator character either at the end of the
// prefix or right after it.
// Example: "/abc" is treated as a prefix of "/abc/def" but not "/abcdef"
// Example: "/abc/" is treated as a prefix of "/abc/def" but not "/abcdef"
prefixLength == 0
|| !char.IsLetterOrDigit(prefix[prefixLength - 1])
|| !char.IsLetterOrDigit(value[prefixLength])
);
}
else
{
return false;
}
}
}
}