_ViewImports.cshtml centralizes Razor directives that would otherwise be repeated across views and pages. Place it in a folder to apply its directives to views and subfolders; placing it in the root Pages folder commonly covers the application’s Razor Pages and partial views. section 17.4.4
Use _ViewImports.cshtml for shared Razor directives, not arbitrary application code:
- Import namespaces with directives such as @using, so views can reference application types without repeating namespace declarations. section 17.4.4
- Share other Razor directives, including @model and @addTagHelper, across the applicable views. section 17.4.4
- Keep executable C# elsewhere: _ViewImports.cshtml accepts Razor directives, while _ViewStart.cshtml is used for common view-start code such as setting Layout. section 17.4.4
- Apply files hierarchically: root-folder files execute first, followed by files in more specific controller or view folders. section 17.5
Typical shared imports
A typical file imports application namespaces and enables the built-in Tag Helpers: @using WebApplication1, @using WebApplication1.Pages, @using WebApplication1.Models, and @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers.
Registering a custom Tag Helper
Register a custom Tag Helper with @addTagHelper CustomTagHelpers.SystemInfoTagHelper, CustomTagHelpers, or register every Tag Helper in the assembly with @addTagHelper *, CustomTagHelpers. The registered helper then becomes available in Razor views, partial views, and layouts. section 32.1.1
