Layout Pages in Web Pages

A typical site needs the same header, navigation bar, and footer on every page, and repeating that markup in every .cshtml file would be both tedious and error-prone whenever a navigation link changes. A layout page solves this by defining the shared HTML skeleton once, conventionally named _SiteLayout.cshtml with a leading underscore to mark it as a helper file that Razor won't serve directly as its own URL, and every content page opts into that skeleton by setting the Layout property at the top of the file and calling RenderBody() to indicate exactly where its own content should be inserted.

Setting Layout to a path pointing at the shared file tells Razor to wrap the current page's output inside that layout's markup at the point where @RenderBody() appears, and any content in the page itself outside of a named @section block becomes exactly what RenderBody() outputs. RenderSection works alongside RenderBody for optional named regions, like a sidebar or a page-specific script block, that not every content page needs to fill in; passing required: false to RenderSection tells the layout it's fine if a given page never defines that section, whereas omitting that argument, or setting it true, throws an exception at runtime for any page missing that section.

Beyond full-page layouts, Web Pages supports smaller reusable fragments through the RenderPage() method, which lets you pull the output of another .cshtml file into the current page at an arbitrary point, useful for something like a repeated product-card widget or a shared search box that appears in multiple places that aren't necessarily the same across the whole site. Unlike Layout, which wraps the calling page, RenderPage() is called from within the page's own content and can even pass data to the partial via an optional second parameter, an object array accessible inside the partial through the PageData collection.