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Service to render views as HTML string in ASP.NET Core
// Inspired by several web solutions and https://raw.githubusercontent.com/aspnet/Mvc/133dd964abb1c2a4167cf38faa38fe0319b7b931/src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/ViewResultExecutor.cs
public class ViewToStringRendererService: ViewExecutor
{
private ITempDataProvider _tempDataProvider;
private IServiceProvider _serviceProvider;
public ViewToStringRendererService(
IOptions<MvcViewOptions> viewOptions,
IHttpResponseStreamWriterFactory writerFactory,
ICompositeViewEngine viewEngine,
ITempDataDictionaryFactory tempDataFactory,
DiagnosticSource diagnosticSource,
IModelMetadataProvider modelMetadataProvider,
ITempDataProvider tempDataProvider,
IServiceProvider serviceProvider)
: base(viewOptions, writerFactory, viewEngine, tempDataFactory, diagnosticSource, modelMetadataProvider)
{
_tempDataProvider = tempDataProvider;
_serviceProvider = serviceProvider;
}
public async Task<string> RenderViewToStringAsync<TModel>(string viewName, TModel model)
{
var context = GetActionContext();
if (context == null) throw new ArgumentNullException(nameof(context));
var result = new ViewResult()
{
ViewData = new ViewDataDictionary<TModel>(
metadataProvider: new EmptyModelMetadataProvider(),
modelState: new ModelStateDictionary())
{
Model = model
},
TempData = new TempDataDictionary(
context.HttpContext,
_tempDataProvider),
ViewName = viewName,
};
var viewEngineResult = FindView(context, result);
viewEngineResult.EnsureSuccessful(originalLocations: null);
var view = viewEngineResult.View;
using (var output = new StringWriter())
{
var viewContext = new ViewContext(
context,
view,
new ViewDataDictionary<TModel>(
metadataProvider: new EmptyModelMetadataProvider(),
modelState: new ModelStateDictionary())
{
Model = model
},
new TempDataDictionary(
context.HttpContext,
_tempDataProvider),
output,
new HtmlHelperOptions());
await view.RenderAsync(viewContext);
return output.ToString();
}
}
private ActionContext GetActionContext()
{
var httpContext = new DefaultHttpContext();
httpContext.RequestServices = _serviceProvider;
return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
}
/// <summary>
/// Attempts to find the <see cref="IView"/> associated with <paramref name="viewResult"/>.
/// </summary>
/// <param name="actionContext">The <see cref="ActionContext"/> associated with the current request.</param>
/// <param name="viewResult">The <see cref="ViewResult"/>.</param>
/// <returns>A <see cref="ViewEngineResult"/>.</returns>
ViewEngineResult FindView(ActionContext actionContext, ViewResult viewResult)
{
if (actionContext == null)
{
throw new ArgumentNullException(nameof(actionContext));
}
if (viewResult == null)
{
throw new ArgumentNullException(nameof(viewResult));
}
var viewEngine = viewResult.ViewEngine ?? ViewEngine;
var viewName = viewResult.ViewName ?? GetActionName(actionContext);
var result = viewEngine.GetView(executingFilePath: null, viewPath: viewName, isMainPage: true);
var originalResult = result;
if (!result.Success)
{
result = viewEngine.FindView(actionContext, viewName, isMainPage: true);
}
if (!result.Success)
{
if (originalResult.SearchedLocations.Any())
{
if (result.SearchedLocations.Any())
{
// Return a new ViewEngineResult listing all searched locations.
var locations = new List<string>(originalResult.SearchedLocations);
locations.AddRange(result.SearchedLocations);
result = ViewEngineResult.NotFound(viewName, locations);
}
else
{
// GetView() searched locations but FindView() did not. Use first ViewEngineResult.
result = originalResult;
}
}
}
if(!result.Success)
throw new InvalidOperationException(string.Format("Couldn't find view '{0}'", viewName));
return result;
}
private const string ActionNameKey = "action";
private static string GetActionName(ActionContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (!context.RouteData.Values.TryGetValue(ActionNameKey, out var routeValue))
{
return null;
}
var actionDescriptor = context.ActionDescriptor;
string normalizedValue = null;
if (actionDescriptor.RouteValues.TryGetValue(ActionNameKey, out var value) &&
!string.IsNullOrEmpty(value))
{
normalizedValue = value;
}
var stringRouteValue = routeValue?.ToString();
if (string.Equals(normalizedValue, stringRouteValue, StringComparison.OrdinalIgnoreCase))
{
return normalizedValue;
}
return stringRouteValue;
}
}
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