Language Service Context for the Core Editor
There are two options for a language service to provide user context using the Visual Studio core editor: provide text marker context, or provide all user context. The differences between each are outlined here.
For more information on providing context to a language service that is connected to your own editor, see How to: Provide Context for Editors or Designers.
Provide Text Marker Context to the Editor
To provide context for compiler errors indicated by text markers in the Visual Studio core editor, implement the IVsTextMarkerContextProvider interface. In this scenario, the language service provides context only when the cursor is on a text marker. This allows the editor to provide the keyword at the cursor to the Dynamic Help window with no attributes.
Provide All User Context to the Editor
If you are creating a language service and are using the Visual Studio core editor, then you can implement the IVsLanguageContextProvider interface to provide context for your language service.
For the implementation of IVsLanguageContextProvider, a context bag (collection) is attached to the editor, which is responsible for updating the context bag. When the Dynamic Help window calls the Update interface on this context bag at idle time, the context bag queries the editor for an update. The editor then notifies the language service that it should update the editor, and passes a pointer to the context bag. This is done by calling the UpdateLanguageContext method from the editor to the language service. Using the pointer to the context bag, the language service can now add and remove attributes and keywords. For more information, see IVsLanguageContextProvider.
There are two different ways to implement IVsLanguageContextProvider:
Provide a keyword to the context bag
When the editor is called to update the context bag, pass in the appropriate keywords and attributes and then return S_OK. This return value instructs the editor to retain your keyword and attribute context rather than provide the keyword at the cursor to the context bag.
Obtain the keyword from the keyword at the cursor
When the editor is called to update the context bag, pass in the appropriate attributes and then return E_FAIL. This return value instructs the editor to retain your attributes in the context bag, but update the context bag with the keyword at the cursor.
The following diagram demonstrates how context is provided for a language service that implements IVsLanguageContextProvider.
Context for a language service
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As you can see in the diagram, the Visual Studio core text editor has a context bag attached to it. This context bag points to three separate subcontext bags: language service, default editor, and text marker. The language service and text marker subcontext bags contain attributes and keywords for the language service if the IVsLanguageContextProvider interface is implemented, and text markers if the IVsTextMarkerContextProvider interface is implemented. If you do not implement either of these interfaces, then the editor provides context for the keyword at the cursor in the default editor subcontext bag.
Context Guidelines for Editors and Designers
Designers and editors must supply a general keyword for the editor or designer window. This is done so that a generic, but appropriate, Help topic will display for the designer or editor when a user presses F1. An editor must, in addition to this, supply the current keyword at the cursor or supply a key term based on the current selection. This is done to ensure that a Help topic for the text or UI element pointed to or selected displays when the user presses F1. A designer supplies context for an item selected in a designer, such as a button on a form. Editors and designers must also connect to a language service as outlined in Language Service Essentials.