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Using a layout

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Specifying a default layout for the app

The application's default layout for all pages is specified in /Components/Routes.razor in the following line of code.

<RouteView RouteData="routeData"
           DefaultLayout="typeof(Layout.MainLayout)" />

The name of the layout is strongly typed. Blazor will only syntax-highlight the code correctly if there is a layout with the name specified. The compiler will also fail if the identifier is incorrect.

Note: If you just wish to alter the appearance of the existing layout you should alter the /Components/Layout/MainLayout.razor file.

Using _Imports.razor

_Imports.razor is a convention used by Blazor to specify defaults. These can be @using declarations for specifying commonly imported namespaces or, in this case, a default @layout to use.

  1. Edit /Components/Routes.razor.
  2. Find the <RouteView> component.
  3. Remove the attribute DefaultLayout="typeof(Layout.MainLayout)".

If you now run the app it will look pretty awful, because there is no layout wrapping any of the pages. To fix this, follow these steps:

  1. Expand the /Components/Pages folder.
  2. Create a new file _Imports.razor.
  3. Add the following content
@layout MainLayout

Now run the app again and note the layout is back.

WARNING: Make sure you edit the _Imports.razor file inside /Components/Pages and not the one directly inside /Components. The reason is /Components/Layout/MainLayout.razor will inherit all code defined inside /Components/_Imports.razor, meaning it will have itself as a layout. Blazor detects circular layout references and throws an InvalidOperationException at runtime rather than hanging.

Specifying a default template for a sub area of the app

If your app has separate areas to it, for example an "Admin" area, it is possible to specify a default layout to use for all pages within that area simply by grouping them within their own child-folder that has its own _Imports.razor file.

We have seen this previously in the Using _Imports.razor section earlier. During Razor compilation, Blazor walks up the folder hierarchy from the page's folder looking for _Imports.razor files. When found, their contents are merged into the top of the generated Razor class. This walk continues to the parent folder, then the grandparent, and so on.

All the imported directives are combined before the Razor source generator produces the compiled class. When a directive can only have a single value ('@layout', @inherits), the value defined in the _Imports.razor closest to the page wins.

_Imports

Example

Create a new Blazor Web App, and then update the navigation menu to contain a link to a new page we'll create shortly.

  1. Open the /Components/Layout/NavMenu.razor file.
  2. Locate the last <div> element, it should contain a <NavLink> component.
  3. Duplicate the <div> element.
  4. Change the NavLink's href attribute to "admin/users".
  5. Change the text inside the <NavLink> to Admin users.

Next we'll create a very basic page

  1. Expand the /Components/Pages node in the Solution Explorer.
  2. Create a folder named Admin.
  3. Create a new file within the folder named AdminUsers.razor.
@page "/admin/users"

<h2>Users</h2>

Note: The URL to the page does not have to reflect the folder structure.

Running the app now will present you with an app that has a new menu item named Admin users. When you click on the item it will show a very basic page that simply says "Users". Next we'll create a default layout for all Admin pages.

  1. Create another new file in the /Components/Pages/Admin folder named _Imports.razor.
  2. Enter the following code:
@layout AdminLayout

At this point there is no file within the app named AdminLayout, so you should see a red-line in Visual Studio beneath the name indicating it cannot be found. You can fix this by creating an AdminLayout.razor in the /Components/Layout/ folder.

@inherits LayoutComponentBase

<h1>Admin</h1>
@Body

If you now run the app and click the Admin users link you will see an awful user experience consisting merely of an h1 and an h2. We will fix this in the section on Nested layouts, but for now we'll use it as an exercise in how to explicitly specify a layout from the page itself.

Specifying a layout explicitly for an individual page

So far we've seen that a default layout can be specified in the /Components/Pages/_Imports.razor file, and we've also seen that this setting can be overridden by Blazor finding a more specific _Imports.razor file in a folder closer to the page it is rendering (/Components/Pages/Admin/_Imports.razor).

The most explicit level of specifying a template to use is to literally specify it in the page itself using the @layout directive.

@page "/admin/users"
@layout MainLayout

<h2>Users</h2>

Running the app again and clicking on the Admin users link will now show basic page using the app's standard layout.

It is also possible to opt out of any layout entirely on a per-page basis by specifying @layout null. This is useful for pages that should render without any surrounding template, such as a full-screen login page.