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.NET Hot Reload support for ASP.NET Core

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.NET Hot Reload applies code changes, including changes to stylesheets, to a running app without restarting the app and without losing app state. Hot Reload is supported for all ASP.NET Core in .NET 6 or later projects.

Generally, updated code is rerun to take effect with the following conditions:

  • Some startup logic is only run once:
    • Middleware, unless the code update is to an inline middleware delegate.
    • Configured services.
    • Route creation and configuration, unless the code update is to a route handler delegate (for example, OnInitialized).
  • In Blazor apps, the framework triggers a Razor component render automatically.
  • In MVC and Razor Pages apps, Hot Reload triggers a browser refresh automatically.
  • Removing a Razor component parameter attribute doesn't cause the component to rerender. The app must be restarted.

For more information on supported scenarios, see Supported code changes (C# and Visual Basic).

Blazor WebAssembly

Blazor WebAssembly Hot Reload supports the following code changes:

  • New types.
  • Nested classes.
  • Most changes to method bodies, such as adding, removing, and editing variables, expressions, and statements.
  • Changes to the bodies of lambda expressions and local functions.
  • Adding static and instance methods to existing types.
  • Adding static and instance fields, events, and properties to existing types.
  • Adding static lambdas to existing methods.
  • Adding lambdas that capture this to existing methods that already captured this previously.

Note that when an attribute is removed that previously set the value of a component parameter, the component is disposed and re-initialized to set the removed parameter back to its default value.

The following code changes aren't supported for Blazor WebAssembly apps:

Blazor WebAssembly Hot Reload supports the following code changes:

  • New types.
  • Nested classes.
  • Most changes to method bodies, such as adding, removing, and editing variables, expressions, and statements.
  • Changes to the bodies of lambda expressions and local functions.
  • Adding static and instance methods to existing types.
  • Adding static fields to existing types.
  • Adding static lambdas to existing methods.
  • Adding lambdas that capture this to existing methods that already captured this previously.

Note that when an attribute is removed that previously set the value of a component parameter, the component is disposed and re-initialized to set the removed parameter back to its default value.

The following code changes aren't supported for Blazor WebAssembly apps:

  • Adding a new await operator or yield keyword expression.
  • Changing the names of method parameters.
  • Adding instance (non-static) fields, events, or properties.

Blazor WebAssembly Hot Reload supports the following code changes:

  • Most changes to method bodies, such as adding, removing, and editing variables, expressions, and statements.
  • Changes to the bodies of lambda expressions and local functions.

The following code changes aren't supported for Blazor WebAssembly apps:

  • Adding new lambdas or local functions.
  • Adding a new await operator or yield keyword expression.
  • Changing the names of method parameters.
  • Changes outside of method bodies.
  • Adding instance (non-static) fields, events, or properties.

.NET CLI

Hot Reload is activated using the dotnet watch command:

dotnet watch

To force the app to rebuild and restart, use the keyboard combination Ctrl+R in the command shell.

When an unsupported code edit is made, called a rude edit, dotnet watch asks you if you want to restart the app:

  • Yes: Restarts the app.
  • No: Doesn't restart the app and leaves the app running without the changes applied.
  • Always: Restarts the app as needed when rude edits occur.
  • Never: Doesn't restart the app and avoids future prompts.

To disable support for Hot Reload, pass the --no-hot-reload option to the dotnet watch command:

dotnet watch --no-hot-reload

Disable Hot Reload

The following setting in Properties/launchSettings.json disables Hot Reload:

"hotReloadEnabled" : false

Additional resources

For more information, see the following resources in the Visual Studio documentation: