One of the many neat functions added to Visual Studio in VS 2010 was the Navigate To feature. You can find it by clicking Edit, Navigate To, or by using the keyboard shortcut Ctrl, (yes, that's control plus the comma key). This pops up the Navigate To dialog that looks like this:

As you type, Navigate To starts searching through a number of different search providers for your term. The entries in the list change as you type, with most providers doing some kind of fuzzy or at least substring matching. If you have C#, C++ or Visual Basic projects in your solution, all symbols defined in those projects are searched. There's also a file search provider, which displays all matching filenames from projects in the current solution as well. And, if you have a Visual Studio package of your own, you can implement a provider too. Micro Focus (where I work) provide the Visual COBOL language inside Visual Studio (http://visualstudiogallery.msdn.microsoft.com/ef9bc810-c133-4581-9429-b01420a9ea40 ), and we wanted to provide this functionality too. This post provides some notes on the things I discovered mainly through trial and error, but also with some kind help from devs inside Microsoft.

The expectation of Navigate To is that it searches across the whole solution, not just the current project. So in our case, we wanted to search for all COBOL symbols inside all of our Visual COBOL projects inside the solution. So first of all, here's the Microsoft documentation on Navigate To: http://msdn.microsoft.com/en-us/library/ee844862.aspx . It's the reference information on the Microsoft.VisualStudio.Language.NavigateTo.Interfaces Namespace, and it lists all the interfaces you will need to implement to create your own Navigate To provider.

Navigate To uses Visual Studio's latest mechanism for integrating external functionality and services, Managed Extensibility Framework (MEF). MEF components don't require any registration with COM or any other registry entries to be found by Visual Studio. Visual Studio looks in several well-known locations for manifest files (extension.vsixmanifest). It then uses reflection to scan for MEF attributes on classes in the assembly to determine which functionality the assembly provides. MEF itself is actually part of the .NET framework, and you can learn more about it here: http://mef.codeplex.com/. To get started with Visual Studio and MEF you could do worse than look at some of the editor examples on the VSX page http://archive.msdn.microsoft.com/vsx . I've also written a small application to help with switching between development and production MEF assemblies, which you can find on Codeproject: http://www.codeproject.com/KB/miscctrl/MEF_Switch.aspx.

The Navigate To interfaces

Back to Navigate To, and summarizing the MSDN reference documentation, you need to implement the following interfaces:

• INavigateToItemProviderFactory
  
  This is Visual Studio's entry point to your Navigate To implementation, and you must decorate your implementation with the following MEF export attribute:

  
  [Export(typeof(INavigateToItemProviderFactory))]

• INavigateToItemProvider
  

  Your INavigateToItemProviderFactory needs to return your implementation of INavigateToItemProvider. This class implements StartSearch() and StopSearch(). StartSearch() is the guts of your provider, and we'll come back to it in a minute. This object also needs to implement IDisposeable().
  

• INavigateToItemDisplayFactory
  

  Your INavigateToItemProvider hands back NavigateToItems to the NavigateTo framework. But to give you good control over what appears in the NavigateTo dialog box, these items will be handed back to your INavigateToItemDisplayFactory, which must create objects implementing INavigateToItemDisplay

   

• INavigateToItemDisplay
  
  Each of these objects represents one result in the Navigate To dialog box. As well as providing the description and name of the item, this object also has a NavigateTo() method that should be capable of displaying the item in an editor when invoked.

Carrying out the search

The lifecycle of your INavigateToItemProvider is the same as that of the Navigate To dialog. This dialog is modal, which makes your implementation a little easier because you know that the user can't be changing things in editors and the IDE while this dialog is up. But the Navigate To dialog DOES NOT run on the main UI thread of the IDE – so you need to be aware of that if you want to interact with editors or other parts of the IDE UI.

When the user invokes the Navigate To dialog, your INavigateToItemProvider gets sent a TryCreateNavigateToItemProvider() message. Instantiate your INavigateToItemProvider and hand this back.

The sequence diagram below shows what happens next. Your INavigateToItemProvider will get called with StartSearch(), and passed an INavigateToCallback. StartSearch() is an asynchronous request – you must return from this method as soon as possible, and conduct your search on a separate thread. For each match to the search term, instantiate a NavigateToItem object and send it to INavigateToCallback.AddItem(). But as the user types in the Search Terms field, NavigateTo will invoke your StartSearch() method repeatedly with the changing search term. When you receive the next StartSearch() message, you have to abandon your current search, and start a new one. You can't rely on receiving a StopSearch() message every time. Finally, when the Navigate To dialog box is closed by the user, you will get a Dispose() message – that's your cue to abandon any uncompleted searches, and dispose any resources you might be using as part of your search.

While you conduct your search invoke INavigateToCallback.ReportProgress() occasionally to provide feedback about how close you are to completing the search. There does not appear to be any particular requirement to how often you invoke ReportProgress(), and you report your progress as the ratio of two integers. In my implementation I report progress in terms of the number of symbols I've searched over the total number of symbols in my dictionary, and send a progress report every 16 symbols.

Displaying the Results

The Navigate to framework invokes INavigateToItemDisplayProvider.CreateItemDisplay() once for each result you passed to the INavigateToCallback. CreateItemDisplay() is passed the NavigateToItem you handed to the callback, and must return an INavigateToItemDisplay object. NavigateToItem is a sealed class which has a few properties, including the name of the symbol. It also has a Tag property, of type object. This enables you to stash away all the information you will need to create your INavigateToItemDisplay, which must implement an INavigateTo() method to display a symbol in an editor IDE when the user double-clicks an entry in the Navigate To dialog box. Since the tag is of type object, it is up to you, the implementor, to decide what kind of object you store in here, and how it enables the retrieval of other information which is not included in the NavigateToItem properties.

Some of the INavigateToItemDisplay properties are self-explanatory, but a couple of them are less obvious:

• Additional information
  
  The string you return here is displayed inside brackets on the same line as the Name property. In English locales, Visual Studio includes the preposition "of". If you look at the first line in the Navigate To screenshot at the top of this article, Book_WebRole.Default is the additional information for textBookAuthor, and is the namespace qualified type name the symbol appears in. For procedural COBOL code we display the Program Id as the additional information
  
• DescriptionItems
  
  You can use this property to return any textual description you want about the item currently selected. You return a collection of DescriptionItem objects, each of which has a category and description collection of DescriptionRun objects. A DescriptionRun enables you to specify some text, and optional formatting, so you have some control over the appearance of the displayed text. The DescriptionItems property is displayed at the bottom of the Navigate To dialog box, with the Categories on the left and the Descriptions on the right. The Visual COBOL implementation uses it to display more information about the location of an item, making it easier for the user to know disambiguate duplicate names (something there can be a lot of in large COBOL applications).

Summary

I hope this article is useful for anyone implementing Navigate To. It is a fantastic navigation feature that Microsoft have added to Visual Studio, but at the moment there still don't seem to be any examples on how to implement it, and the reference information on MSDN is a little brief for anyone attempting an implementation.