Context-sensitive components

• Using _ContextMixin to access context in components
• Changing the current context
• Listening to changes to the current context using subscription
• Implementing a context resolver on the server
• Querying for a new context by URL
• ContextHistory and navigating back to previous context

How it works

Episerver supports context-sensitive client components. Context could be the current page that the user is working with. Because components are loosely coupled, the context service object is responsible for handling the current context. To get hold of the current context you could simply do this:

var contextService = epi.dependency.resolve("epi.shell.ContextService");
var currentContext = contextService.currentContext;

The context service on the client interacts with the server to resolve context for the selected page/block/entity. The actual properties on the context object depends on the type of context being displayed but a few properties are available for all context:

Context on the server implements the IClientContext interface and is serialized to the client.

Example: epi.cms.contentdata Context

JavaScript

{
    "parentLink":"4",
    "customViewType":"",
    "language":"en",
    "publicUrl":"/MaintAlloy/Alloy-Track/",
    "capabilities":
    {
        "languageSettings":true,
        "securable":true,
        "dynamicProperties":true,
        "isFolder":false,
        "isPage":true,
        "contentResources":true,
        "language":true,
        "isBlock":false
    },
    "languageContext":
    {
        "isTranslationNeeded":false,
        "language":"en",
        "isPreferredLanguageAvailable":true,
        "preferredLanguage":"en",
        "reason":1,
        "warning":null,
        "hasTranslationAccess":true
    },
    "hasSiteChanged":false,
    "fullHomeUrl":"http://localhost/MaintAlloy/EPiServer/CMS/Home",
    "versionedUrl":"",
    "dataType":"epi.cms.page",
    "uri":"epi.cms.contentdata:///8_8",
    "previewUrl":"/MaintAlloy/EPiServer/CMS/Alloy-Track,,8_8/?id=8_8&epieditmode=true",
    "data":null,
    "name":"Alloy Track",
    "requestedUri":"epi.cms.contentdata:///8",
    "versionAgnosticUri":"epi.cms.contentdata:///8"
}

Using _ContextMixin to access context in components

To simplify interaction with the context you can implement a mix-in that provides access to the context from a component.

define("epi-cms/component/PageVersions", [
    "epi/shell/_ContextMixin"
], function (_ContextMixin) {
    return dojo.declare("epi.cms.component.PageVersions", [_ContextMixin], {
        constructor: function(){
            dojo.when(this.getCurrentContext(), function(context){
                console.log("we have context: ", context);
            });
        }
    }
});

The _ContextMixin extends the class with a the following methods:

Changing the current context

If you need to change the current context, publish a message to the /epi/shell/context/request channel with parameters for the new context as the data. A URI parameter property is required to determine which type of context to load. The following example changes the current context to an Episerver CMS ContentData object:

var pageLink = "5_135"; //Replace with code to determine the pageLink for the page you want to change to..
var contextParameters = { uri: 'epi.cms.contentdata:///' + pageLink };
dojo.publish("/epi/shell/context/request", [contextParameters]);

Listening to changes to the current context using subscription

Without using _ContextMixin, you can subscribe to context changes using the dojo pub/sub infrastructure. If you want to react to a context change, subscribe to the /epi/shell/context/changed message:

startup: function () {
    this.subscribe("/epi/shell/context/changed", this._contextChanged);
},
_contextChanged: function (newContext) {
    if (!newContext) {
        return;
    }
    //Do something with newContext.
}

Implementing a context resolver on the server

To provide context for a certain type of entities you can implement the following context resolver interfaces.

• Resolve a known reference using URI.
• Query context on a specific URL.

The following example shows a context resolver that performs both these tasks:

/// Resolves URIs and URLs to files for the shell context service.
[ServiceConfiguration(typeof(IUrlContextResolver))]
[ServiceConfiguration(typeof(IUriContextResolver))]
public class CmsFileContextResolver : IUriContextResolver, IUrlContextResolver
{
    private VirtualPathProvider _vpp;

    public CmsFileContextResolver(VirtualPathProvider vpp)
    {
        SortOrder = 123;
        _vpp = vpp;
    }

    /// The name of the model the context contextualizes.
    public string Name
    {
        get { return "epi.cms.unifiedfile"; }
    }

    /// Resolves a page link in URI format.
    public bool TryResolveUri(Uri uri, out IClientContext instance)
    {
        instance = ResolvePath("~" + uri.LocalPath);
        return instance != null;
    }

    /// Tries to resolve an url to page context.
    public bool TryResolveUrl(Uri url, out IClientContext instance)
    {
        instance = ResolvePath(url.LocalPath);
        return instance != null;
    }

    private IClientContext ResolvePath(string path)
    {
        var file = _vpp.GetFile(path) as UnifiedFile;
        if (file == null)
        {
            return null;
        }
        return new Models.UnifiedFileContext
        {
            Uri = new Uri("epi.file.unifiedfile://" + VirtualPathUtilityEx.ToAppRelative(file.VirtualPath).TrimStart('~')),
            Data = new
            {
                file.VirtualPath,
                // ... more unifiedfile-specific data
            },
            PreviewUrl = file.VirtualPath
        };
    }

    /// Sort order among peer url resolvers.
    public int SortOrder { get; set; }
}

Querying for a new context by URL

Context resolvers that implement the IUrlContextResolver interface are queried when you load a URL in the preview frame. Publish a message to programmatically change the context to the context associated with a URL, as shown in the following example. 

// queries the context service for the context belonging to a URL
var contextParameters = { url: someUnknownUrl.toString() };
dojo.publish("/epi/shell/context/request", [contextParameters, { sender: this }]);

define("epi-cms/contextNavigation", function (contextNavigation) {
    return dojo.declare("epi.cms.component.MyCustomeView", {
        clicked: function(){
            contextNavigation.back(this);
        }
    }
});