5.6 KiB
| title | author | description | monikerRange | ms.author | ms.custom | ms.date | uid |
|---|---|---|---|---|---|---|---|
| Control head content in ASP.NET Core Blazor apps | guardrex | Learn how to control head content in Blazor apps, including how to set the page title from a component. | >= aspnetcore-6.0 | riande | mvc | 11/08/2022 | blazor/components/control-head-content |
Control <head> content in ASP.NET Core Blazor apps
Razor components can modify the HTML <head> element content of a page, including setting the page's title (<title> element) and modifying metadata (<meta> elements).
Control <head> content in a Razor component
Specify the page's title with the xref:Microsoft.AspNetCore.Components.Web.PageTitle component, which enables rendering an HTML <title> element to a HeadOutlet component.
Specify <head> element content with the xref:Microsoft.AspNetCore.Components.Web.HeadContent component, which provides content to a HeadOutlet component.
The following example sets the page's title and description using Razor.
Pages/ControlHeadContent.razor:
:::moniker range=">= aspnetcore-7.0"
:::code language="razor" source="~/../blazor-samples/7.0/BlazorSample_WebAssembly/Pages/control-head-content/ControlHeadContent.razor" highlight="13,15-17":::
:::moniker-end
:::moniker range="< aspnetcore-7.0"
:::code language="razor" source="~/../blazor-samples/6.0/BlazorSample_WebAssembly/Pages/control-head-content/ControlHeadContent.razor" highlight="13,15-17":::
:::moniker-end
:::moniker range="< aspnetcore-7.0"
Control <head> content during prerendering
This section applies to prerendered Blazor WebAssembly apps and Blazor Server apps.
When Razor components are prerendered, the use of a layout page (_Layout.cshtml) is required to control <head> content with the xref:Microsoft.AspNetCore.Components.Web.PageTitle and xref:Microsoft.AspNetCore.Components.Web.HeadContent components. The reason for this requirement is that components that control <head> content must be rendered before the layout with the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component. This order of rendering is required to control head content.
If the shared _Layout.cshtml file doesn't have a Component Tag Helper for a xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component, add it to the <head> elements.
In a required, shared _Layout.cshtml file of a Blazor Server app or Razor Pages/MVC app that embeds components into pages or views:
<component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />
In a required, shared _Layout.cshtml file of a prerendered hosted Blazor WebAssembly app:
<component type="typeof(HeadOutlet)" render-mode="WebAssemblyPrerendered" />
:::moniker-end
HeadOutlet component
The xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component renders content provided by xref:Microsoft.AspNetCore.Components.Web.PageTitle and xref:Microsoft.AspNetCore.Components.Web.HeadContent components.
In an app created from the Blazor WebAssembly project template, the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component is added to the xref:Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder.RootComponents collection of the xref:Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder in Program.cs:
builder.RootComponents.Add<HeadOutlet>("head::after");
When the ::after pseudo-selector is specified, the contents of the root component are appended to the existing head contents instead of replacing the content. This allows the app to retain static head content in wwwroot/index.html without having to repeat the content in the app's Razor components.
:::moniker range=">= aspnetcore-7.0"
In Blazor Server apps created from the Blazor Server project template, a Component Tag Helper renders <head> content for the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component in Pages/_Host.cshtml:
:::moniker-end
:::moniker range="< aspnetcore-7.0"
In Blazor Server apps created from the Blazor Server project template, a Component Tag Helper renders <head> content for the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component in Pages/_Layout.cshtml:
:::moniker-end
<head>
...
<component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />
</head>
Not found page title
In Blazor apps created from Blazor project templates, the NotFound component template in the App component (App.razor) sets the page title to Not found.
App.razor:
<PageTitle>Not found</PageTitle>
Additional resources
Mozilla MDN Web Docs documentation: