Get current Url in a Blazor component

问题:

I need to know the url of the current page in order to check if I have to apply certain style to a element. The code below is an example.

@using Microsoft.AspNetCore.Blazor.Services
@inject IUriHelper UriHelper
@implements IDisposable

<h1>@url</h1>
<nav>
    <div class="nav-wrapper">
        <a href="#" class="brand-logo">Blazor</a>
        <ul id="nav-mobile" class="right hide-on-med-and-down">
            <li>
                <NavLink href="/" Match=NavLinkMatch.All>
                    Home
                </NavLink>
            </li>
            <li>
                <NavLink href="/counter">
                    Counter
                </NavLink>
            </li>
            <li>
                <NavLink href="/fetchdata">
                    Fetch data
                </NavLink>
            </li>
        </ul>
    </div>
</nav>

@functions {

    private string url = string.Empty;

    protected override void OnInit()
    {
        url = UriHelper.GetAbsoluteUri();
        UriHelper.OnLocationChanged += OnLocationChanged;
    }

    private void OnLocationChanged(object sender, LocationChangedEventArgs e)
    {
        url = newUriAbsolute;
    }

    public void Dispose()
    {
        UriHelper.OnLocationChanged -= OnLocationChanged;
    }
}

I used the same approach used in the NavLink component in the Blazor repository, but it did not work. Any ideas?.

回答1:

Use Uri property from NavigationManager class.

How it works

Get it from injection before to use it on .razor pages:

@inject NavigationManager MyNavigationManager

Or like this on .cs if you prefer "code-behind" experience:

using Microsoft.AspNetCore.Components;
...
[Inject] 
public NavigationManager MyNavigationManager {get; set;}

Sample

@page "/navigate"
@inject NavigationManager MyNavigationManager

<h1>Current url</h1>

<p>@(MyNavigationManager.Uri)</p>

More about navigation (NavigateTo, BaseUri, ToAbsoluteUri, ToBaseRelativePath, ... ) at: URI and navigation state helpers

NavigationManager cheatsheet

MyNavigationManager.Uri
#> https://localhost:5001/counter/3?q=hi

MyNavigationManager.BaseUri`
#> https://localhost:5001/

MyNavigationManager.NavigateTo("http://new location")
#> Navigates to new location

MyNavigationManager.LocationChanged
#> An event that fires when the navigation location has changed.

MyNavigationManager.ToAbsoluteUri("pepe")
#> https://localhost:5001/pepe

MyNavigationManager.ToBaseRelativePath( MyNavigationManager.BaseUri)
#> counter/3?q=hi

Helper: AddQueryParm( "q2", "bye" )
#> https://localhost:5001/counter/3?q=hi&q2=bye

Helper: GetQueryParm( "q" )
#> hi

Helpers code:

@code {

[Parameter]
public string Id { get; set; }

// blazor: add parm to url
string AddQueryParm(string parmName, string parmValue)
{
    var uriBuilder = new UriBuilder(MyNavigationManager.Uri);
    var q = System.Web.HttpUtility.ParseQueryString(uriBuilder.Query);
    q[parmName] = parmValue;
    uriBuilder.Query = q.ToString();
    var newUrl = uriBuilder.ToString();
    return newUrl;
}

// blazor: get query parm from url
string GetQueryParm(string parmName)
{
    var uriBuilder = new UriBuilder(MyNavigationManager.Uri);
    var q = System.Web.HttpUtility.ParseQueryString(uriBuilder.Query);
    return q[parmName] ?? "";
}

}

回答2:

There is no use in connecting to the OnLocationChanged event in a page or component, as they get loaded and disposed on demannd.

You should register to this event in app.cshtml as that won't be disposed.

回答3:

You should listen to a LocationChange of the IUriHelper, which triggers the function to do what you want for example:

@using Microsoft.AspNetCore.Blazor.Components
@using Microsoft.Extensions.Logging
@inject Microsoft.AspNetCore.Blazor.Services.IUriHelper UriHelper
@inject ILogger<NavItem> logger

<li class="m-menu__item @(Active ? "m-menu__item--active" : "")">
    <a href=@Url class="m-menu__link ">
        <span class="m-menu__item-here"></span>
        <i class="m-menu__link-icon @Icon"></i>
        <span class="m-menu__link-text">@Text</span>
    </a>
</li>

@functions {
    protected override void OnInit()
    {
        UriHelper.OnLocationChanged += OnLocationChanges;
    }
    [Parameter]
    private string Url { get; set; }
    [Parameter]
    private string Icon { get; set; }
    [Parameter]
    private string Text { get; set; }
    private bool Active = false;
    private void OnLocationChanges(object sender, string newLocation)
    {
        bool active = newLocation.Contains(Url);
        if(active != Active) //Only re-render the components that need it
        {
            Active = active;
            StateHasChanged();
            logger.LogInformation("Location Change To:" + newLocation);
        }
    }
}