[Asp.Net Core] Blazor Server Side 项目实践 - 切换页面时保留状态

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Components.Rendering;
using System.Reflection;

namespace Microsoft.AspNetCore.Components   //use this namepace so copy/paste this code easier
{

    public class KeepPageStateRouteView : RouteView
    {
        protected override void Render(RenderTreeBuilder builder)
        {
            var layoutType = RouteData.PageType.GetCustomAttribute()?.LayoutType ?? DefaultLayout;
            builder.OpenComponent(0);
            builder.AddAttribute(1, "Layout", layoutType);
            builder.AddAttribute(2, "ChildContent", (RenderFragment)CreateBody());
            builder.CloseComponent();
        }

        RenderFragment CreateBody()
        {
            var pagetype = RouteData.PageType;
            var routeValues = RouteData.RouteValues;

            void RenderForLastValue(RenderTreeBuilder builder)
            {
                //dont reference RouteData again

                builder.OpenComponent(0, pagetype);
                foreach (KeyValuePairstring, object> routeValue in routeValues)
                {
                    builder.AddAttribute(1, routeValue.Key, routeValue.Value);
                }
                builder.CloseComponent();
            }

            return RenderForLastValue;
        }

    }

}

@inherits LayoutComponentBase

@inject NavigationManager navmgr

@code{

    TimeSpan GetUrlMaxLifeSpan(string url)
    {
        if (url.Contains("/fetchdata")) // Let /fetachdata always refresh
            return TimeSpan.Zero;

        if (url.Contains("/counter"))   // Let /counter expires in 10 seconds
            return TimeSpan.FromSeconds(10);

        return TimeSpan.FromSeconds(-1);    //other pages never expires
    }

    class PageItem
    {
        public string Url;
        public RenderFragment PageBody;
        public DateTime StartTime = DateTime.Now;
        public DateTime ActiveTime = DateTime.Now;
        public TimeSpan MaxLifeSpan;
    }

    Dictionarystring, PageItem> bodymap = new Dictionarystring, PageItem>();

    int mainRenderCount = 0;
}

div class="sidebar">
    NavMenu />
div>

div class="main">


    @{

        bool currurlrendered = false;

        string currenturl = navmgr.Uri;

        PageItem curritem;
        if (bodymap.TryGetValue(currenturl, out curritem))
        {
            curritem.ActiveTime = DateTime.Now;
        }
        else
        {
            curritem = new PageItem { Url = currenturl, PageBody = Body };
            curritem.MaxLifeSpan = GetUrlMaxLifeSpan(currenturl);
            if (curritem.MaxLifeSpan != TimeSpan.Zero)
            {
                bodymap[navmgr.Uri] = curritem;
            }
        }

        mainRenderCount++;

    }

    div class="top-row px-4">


        #@mainRenderCount

        , CurrentUrl : @currenturl

        . PageCount : @bodymap.Count
        ,
        button @onclick="StateHasChanged">StateHasChangedbutton>

    div>


    @foreach (PageItem eachitem in bodymap.Values.ToArray())
    {

        string pageurl = eachitem.Url;
        RenderFragment pagebody = eachitem.PageBody;

        string divstyle = "display:none";
        if (pageurl == currenturl)
        {
            divstyle = "";
            currurlrendered = true;
        }
        else if (eachitem.MaxLifeSpan.TotalSeconds > 0 && DateTime.Now - eachitem.ActiveTime > eachitem.MaxLifeSpan)
        {
            bodymap.Remove(eachitem.Url);
            continue;
        }

        div @key="pageurl" class="content px-4" style="@divstyle">
            @pagebody
        div>
    }

    @if (!currurlrendered)
    {
        div class="content px-4">
            @Body
        div>
    }

div>