QueryStringNavigationExamples.razor

@inject NavigationManager navigationManager

... 

@code {
    // example code to change state based on the querystring.  
    // Call perhaps from an event callback or  whenever the query may have changed.
    private void LoadFromQuery()
    {
        Uri uri = navigationManager.ToAbsoluteUri(navigationManager.Uri);
        Dictionary<string, StringValues> query = ParseQuery(uri.Query);
        var keys = query.Keys.ToArray();

        foreach (string key in keys)
        {
            if (key == "section")
            {
                string sectionValue = query.TryGet(key);
                ShowSection(sectionValue)
            }
            else
            {
                ...
            }
        }
    }
    
    /// <summary>
    /// Parse a query string into its component key and value parts.
    /// </summary>
    /// <param name="queryString">The raw query string value, with or without the leading '?'.</param>
    /// <returns>A collection of parsed keys and values.</returns>
    public static Dictionary<string, StringValues> ParseQuery(string queryString)
    {
        var result = ParseNullableQuery(queryString);

        if (result == null)
        {
            return new Dictionary<string, StringValues>();
        }

        return result;
    }


    /// <summary>
    /// Parse a query string into its component key and value parts.
    /// </summary>
    /// <param name="queryString">The raw query string value, with or without the leading '?'.</param>
    /// <returns>A collection of parsed keys and values, null if there are no entries.</returns>
    public static Dictionary<string, StringValues> ParseNullableQuery(string queryString)
    {
        var accumulator = new KeyValueAccumulator();

        if (string.IsNullOrEmpty(queryString) || queryString == "?")
        {
            return null;
        }

        int scanIndex = 0;
        if (queryString[0] == '?')
        {
            scanIndex = 1;
        }

        int textLength = queryString.Length;
        int equalIndex = queryString.IndexOf('=');
        if (equalIndex == -1)
        {
            equalIndex = textLength;
        }
        while (scanIndex < textLength)
        {
            int delimiterIndex = queryString.IndexOf('&', scanIndex);
            if (delimiterIndex == -1)
            {
                delimiterIndex = textLength;
            }
            if (equalIndex < delimiterIndex)
            {
                while (scanIndex != equalIndex && char.IsWhiteSpace(queryString[scanIndex]))
                {
                    ++scanIndex;
                }
                string name = queryString.Substring(scanIndex, equalIndex - scanIndex);
                string value = queryString.Substring(equalIndex + 1, delimiterIndex - equalIndex - 1);
                accumulator.Append(
                    Uri.UnescapeDataString(name.Replace('+', ' ')),
                    Uri.UnescapeDataString(value.Replace('+', ' ')));
                equalIndex = queryString.IndexOf('=', delimiterIndex);
                if (equalIndex == -1)
                {
                    equalIndex = textLength;
                }
            }
            else
            {
                if (delimiterIndex > scanIndex)
                {
                    accumulator.Append(queryString.Substring(scanIndex, delimiterIndex - scanIndex), string.Empty);
                }
            }
            scanIndex = delimiterIndex + 1;
        }

        if (!accumulator.HasValues)
        {
            return null;
        }

        return accumulator.GetResults();
    }

    public static class NavigationExtensions {
        /// <summary>
        /// Navigates to the current URI, but with a different query string.
        /// </summary>
        public static void NavigateToQuery(this NavigationManager navigationManager, QueryString newQueryString) =>
            navigationManager.NavigateTo(navigationManager.Uri.WithQuery(newQueryString));
        /// <summary>
        /// Returns a copy of a string URL with its query string replaced with a new one.
        /// </summary>
        private static string WithQuery(this string url, QueryString newQueryString) =>
            new UriBuilder(url) { Query = newQueryString.ToString() }.ToString();


    }
}