Action filters

In large apps and sites, you need to do apply global actions e.g. for each button click on a specific page, section or even on all pages in the app. Additionally, you may want to do global exception handling and logging, or switch the culture based on a value from cookies etc.

In DotVVM, we have a concept of filters. If you know Action filters in ASP.NET MVC, it is the same thing.

Filter events

If you want to apply a common logic to one or more viewmodels, viewmodel commands or a whole application, you need to create a class that derives from ActionFilterAttribute.

You can then override any of the method listed below.

• Presenter-level events (applicable to DotVVM pages and custom presenters)

  • OnPresenterExecutingAsync is executed immediately after the URL is mapped to a specific route and presenter is resolved. This method is called also for DotVVM pages as they are handled by DotvvmPresenter class.
  • OnPresenterExecutedAsync is executed immediately after the presenter completes processing of the request. This method is called also for DotVVM pages as they are handled by DotvvmPresenter class.
  • OnPresenterExceptionAsync is executed when an unhandled exception is thrown from the presenter. This method is called also for DotVVM pages as they are handled by DotvvmPresenter class.

• Page-level events (applicable to DotVVM pages)

  • OnPageInitializedAsync is executed after the page control tree is built and viewmodel instance is initialized.
  • OnPageRenderedAsync is executed after the response is rendered completely and before the viewmodel instance is disposed.
  • OnPageExceptionAsync is executed when an unhandled exception occurs during the processing of the DotVVM page.

• ViewModel-level events (applicable to DotVVM pages)

  • OnViewModelCreatedAsync is executed after the viewmodel instance is created and assigned to the root of the control tree, and the PreInit phase is completed.
  • OnViewModelSerializingAsync is executed after the PreRenderComplete phase is completed and before the viewmodel is serialized to JSON.
  • OnViewModelDeserializedAsync is executed on postbacks, after the viewmodel from the client was deserialized, before the Load phase is initiated.

• Command-level events (applicable to postbacks on DotVVM pages)

  • OnCommandExecutingAsync is executed on postbacks, before the command referenced from a command binding is called.
  • OnCommandExecutedAsync is executed on postbacks, after the command referenced from a command binding is called.

There is also a class called ExceptionFilterAttribute which adds another event:

• OnCommandException is executed on postbacks, when the command referenced from a command binding throws an exception.

If you only need to target specific events, you don't need to inherit from these attributes. You can implement the IPresenterActionFilter, IPageActionFilter, ICommandActionFilter or IViewModelActionFilter interface instead.

See also

• Filters
• Exception filters
• Authentication and authorization