如何将完整的RazorPage渲染为字符串？

要将完整的RazorPage渲染为字符串，可以通过以下步骤实现：

基础概念

RazorPage是ASP.NET Core中的一个组件，用于处理HTTP请求并生成HTML响应。渲染RazorPage为字符串意味着在不发送HTTP响应的情况下，获取其生成的HTML内容。

类型与应用场景

类型：主要涉及RazorPage的渲染逻辑。
应用场景：包括但不限于API生成HTML片段、后台任务生成报告、邮件模板渲染等。

实现步骤

以下是一个简单的示例，展示如何将RazorPage渲染为字符串：

步骤1：创建RazorPage

首先，确保你有一个RazorPage。例如，Pages/Index.cshtml:

@page
@model IndexModel
<h1>Hello, @Model.Name!</h1>

对应的Index.cshtml.cs:

public class IndexModel : PageModel
{
    public string Name { get; set; }

    public void OnGet()
    {
        Name = "World";
    }
}

步骤2：编写渲染逻辑

创建一个服务或方法来渲染RazorPage为字符串：

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using System.IO;
using System.Threading.Tasks;

public interface IRazorViewRenderer
{
    Task<string> RenderToStringAsync(string viewName, object model);
}

public class RazorViewRenderer : IRazorViewRenderer
{
    private readonly IRazorViewEngine _razorViewEngine;
    private readonly ITempDataProvider _tempDataProvider;
    private readonly IServiceProvider _serviceProvider;

    public RazorViewRenderer(
        IRazorViewEngine razorViewEngine,
        ITempDataProvider tempDataProvider,
        IServiceProvider serviceProvider)
    {
        _razorViewEngine = razorViewEngine;
        _tempDataProvider = tempDataProvider;
        _serviceProvider = serviceProvider;
    }

    public async Task<string> RenderToStringAsync(string viewName, object model)
    {
        var httpContext = new DefaultHttpContext { RequestServices = _serviceProvider };
        var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

        using (var sw = new StringWriter())
        {
            var viewResult = _razorViewEngine.FindView(actionContext, viewName, false);

            if (viewResult.View == null)
            {
                throw new ArgumentNullException($"{viewName} does not match any available view");
            }

            var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
            {
                Model = model
            };

            var viewData = new ViewFeatures.ViewDataDictionary(viewDictionary);
            var tempData = new ViewFeatures.TempDataDictionary(actionContext.HttpContext, _tempDataProvider);

            var bodyWriter = new BodyWriter(sw);
            var viewWriter = new ViewWriter(bodyWriter);

            var view = viewResult.View;
            await view.RenderAsync(viewWriter, viewData, tempData);

            return sw.ToString();
        }
    }

    private class BodyWriter : IBodyWriter
    {
        private readonly TextWriter _writer;

        public BodyWriter(TextWriter writer)
        {
            _writer = writer;
        }

        public void WriteBytes(byte[] bytes) => _writer.Write(Encoding.UTF8.GetString(bytes));

        public Task WriteAsync(byte[] buffer, int offset, int count)
        {
            _writer.Write(Encoding.UTF8.GetString(buffer, offset, count));
            return Task.CompletedTask;
        }
    }

    private class ViewWriter : IViewWriter
    {
        private readonly IBodyWriter _bodyWriter;

        public ViewWriter(IBodyWriter bodyWriter)
        {
            _bodyWriter = bodyWriter;
        }

        public Task WriteAsync(ReadOnlySequence<byte> data)
        {
            var buffer = data.ToArray();
            _bodyWriter.WriteBytes(buffer);
            return Task.CompletedTask;
        }
    }
}

步骤3：注册服务并使用

在Startup.cs中注册该服务：

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages();
    services.AddScoped<IRazorViewRenderer, RazorViewRenderer>();
}

然后在需要的地方注入并使用：

public class SomeService
{
    private readonly IRazorViewRenderer _renderer;

    public SomeService(IRazorViewRenderer renderer)
    {
        _renderer = renderer;
    }

    public async Task<string> GetIndexPageHtml()
    {
        return await _renderer.RenderToStringAsync("Index", new { Name = "World" });
    }
}