Anonymous or Substitute Handlers

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Substitute handlers/delegates are deprecated and will be removed from Blender.MapUri in Starcounter 2.4. Please use normal handlers instead.
Introduction
Sometimes, it is required to get a partial without declaring a handler. This is when anonymous handlers became handy.
model.Partial = Self.GET("/custom-url", () =>
{
    return new Page()
    {
        Html = "/custom-page.html"
    };
});
The model.Partial will contain the returned new Page() and all the responses from all the apps mapped to the "/custom-url". The anonymous handler can be called to any url.
Things to Know About Anonymous Handlers
The anonymous handlers should never be used for direct calls to handlers defined in other apps. Follow the practice that the apps should not be aware of each other.
An app can only have one response per URL, that is why anonymous handlers can't be combined with declared ones.
The Html property is not required, it may be blank if the calling app does not have any response.
The anonymous handler response should be of type Starcounter.Page otherwise it won't be possible to merge with other responses.
When to Use Anonymous Handlers
Shared UI Sections
The most common case is the Launcher. The Launcher defines different UI sections and populates them with anonymous Self.GET requests.
//UriMapping.MappingUriPrefix - a constant, equals to "/sc/mapping"
model.Menu = Self.GET(UriMapping.MappingUriPrefix + "/menu", () => new Page());
The model.Menu contains merged responses from all handlers mapped to /sc/mapping/menu. The mapping would look like this:
UriMapping.Map("/Products/menu", UriMapping.MappingUriPrefix + "/menu");
Read more about mapping here: Mixing apps.
UI View Composition with Layout Editor
Composition technology requires some extra HTML elements and JSON wrapping which are injected per partial using middleware. This means that partials which are created without a request won't be available for view composition.
// The IndexPage is available for view composition.
// It is retrieved with a request.
Handle.GET("/my-app", () => new IndexPage());
Handle.GET("/my-app", () => new MasterPage()
{
    // The IndexPage is not available for view composition.
    // It is retrieved without a request.
    CurrentPage = new IndexPage()
});
// The MasterPage and the IndexPage are both retrieved
// with a request and available for view composition.
Handle.GET("/my-app", () => MasterPage()
{
    CurrentPage = Self.GET("/my-app/partials/index")
});
​
Handle.GET("/my-app/partials/index", () => new IndexPage());
An anonymous handler can be used instead of the custom partial handler definition.
// The IndexPage is still available for view composition,
// It is retrieved with an anonymous request.
Handle.GET("/my-app", () => MasterPage()
{
    CurrentPage = Self.GET("/my-app/partials", () => new IndexPage())
});
Middleware
URL Aliases and Redirects
Last modified 4yr ago
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Outline
Introduction
Things to Know About Anonymous Handlers
When to Use Anonymous Handlers
Shared UI Sections
UI View Composition with Layout Editor