Host class

The root API the IDE passes to every addin. The DLL receives a Host as the argument to its tbCreateCompilerAddin factory; the addin holds onto that reference for its lifetime and reaches every other capability through it — the currently-loaded CurrentProject, the ActiveEditors, the Toolbars for adding buttons, the ToolWindows for adding HTML-rendered panels, the DebugConsole for log output, the virtual FileSystem, the KeyboardShortcuts registry, the Themes state, plus the dialog helpers ShowMessageBox / ShowNotification.

Typically held via WithEvents so the addin can subscribe to lifecycle events:

Private WithEvents Host As Host

Public Sub New(ByVal Host As Host)
    Set Me.Host = Host
End Sub

Private Sub Host_OnProjectLoaded()
    With Host.Toolbars(0)
        .AddSplitter
        Set MyButton = .AddButton("MyButton", "My Action")
    End With
End Sub

Almost every meaningful addin builds its toolbar buttons and tool windows inside the OnProjectLoaded handler — that is the first moment the IDE is fully ready to accept extensibility commands.

Properties
Methods
Events
DebuggerEvaluateOptions

Properties

ActiveEditors

The collection of editors currently open in the IDE. Use Host.ActiveEditors(0) for the active one — at present the IDE exposes exactly one active editor at a time and Host.ActiveEditors.Count is 1 when an editor is open, 0 when none is. As Editors. Read-only.

CompilerVersion

The full compiler-version string of the running IDE, e.g. "0.15.371". String, read-only. Useful for diagnostic log lines and for compatibility gates.

CurrentProject

The currently-loaded project. Provides project name and path, lifecycle methods (Save / Close / Build / Clean), the project’s RootFolder into the virtual file system, expression evaluation against the running project context, and persistent meta-data storage inside the .twinproj file. As Project. Read-only.

DebugConsole

The IDE’s DEBUG CONSOLE pane. Print, clear, or set focus. As DebugConsole. Read-only.

FileSystem

The IDE’s virtual file system — the abstraction that lets the addin walk and read source files without touching the on-disk paths. As FileSystem. Read-only.

IDEProcessID

The OS process ID of the running IDE process. Long, read-only. Useful for inter-process scenarios — e.g. an external helper EXE that needs to know which IDE invoked it.

IDEWindowHandle

The Win32 HWND of the IDE’s main window. LongPtr, read-only. Pass to Win32 APIs that need a window owner, or use as the parent handle when displaying owned modal dialogs from the addin.

KeyboardShortcuts

The keyboard-shortcut registry. Use KeyboardShortcuts.Add to bind a key combination to a callback. As KeyboardShortcuts. Read-only.

Themes

The IDE’s theme state. Exposes the active theme name and group; pair with the OnChangedTheme event to react to user theme changes. As Themes. Read-only.

Toolbars

The collection of IDE toolbars. Currently a one-element collection — Host.Toolbars(0) is the only available toolbar. As Toolbars. Read-only.

ToolWindows

Factory for HTML-rendered tool windows. Use ToolWindows.Add to create one. As ToolWindows. Read-only.

Methods

ShowMessageBox

Displays a modal IDE-styled dialog with a customisable button strip. Returns the zero-based index of the pressed button, or -1 if the dialog was closed without picking one.

Syntax: host.ShowMessageBox( Prompt, Buttons, Title ) As Long

Prompt: required The message to display. String.
Buttons: required A String of button captions separated by |. E.g. "OK" for a single OK button, "Yes|No|Cancel" for three buttons.
Title: required The dialog’s title-bar text. String.

Select Case Host.ShowMessageBox("Save changes before closing?", _
                                 "Save|Discard|Cancel", "Confirm")
    Case 0: ' Save
    Case 1: ' Discard
    Case 2, -1: ' Cancel or closed
End Select

ShowNotification

Displays a non-modal, discreet notification pop-up in the IDE — a toast-style transient message that does not require the user to react.

Syntax: host.ShowNotification Prompt

Prompt: required The notification text. String.

Use ShowMessageBox when the user has to answer something; ShowNotification is for “the user should know but doesn’t have to react”.

Events

The Host CoClass exposes three events. The third (and any future addition) is tagged with the compile-time [AllowUnpopulatedVtableEntry] attribute, which lets a newer addin compile against the newer events interface and still load against an older IDE that does not yet fire the newer event — older IDEs simply leave the slot empty and the addin never receives that particular event.

OnProjectLoaded

Fires once the IDE has finished loading the project and is ready to accept extensibility commands. The canonical place to set up toolbar buttons, open tool windows that should be visible by default, register keyboard shortcuts, and log the start-up state to the DebugConsole.

Syntax: host_OnProjectLoaded()

Private Sub Host_OnProjectLoaded()
    With Host.Toolbars(0)
        .AddSplitter
        Set MyButton = .AddButton("MyButton", "My Action")
    End With
End Sub

OnChangedActiveEditor

Fires when the user switches the focused editor. Use this to refresh any addin UI that depends on the current editor (e.g. a context-aware tool window). Available since IDE BETA 504+; older IDEs simply do not fire it.

Syntax: host_OnChangedActiveEditor(EditorIdx As Long, Editor As Editor)

EditorIdx: The zero-based index of the newly active editor in the ActiveEditors collection.
Editor: The newly active editor object. Castable to CodeEditor for code panes — see Editor castability.

OnChangedTheme

Fires when the user changes the IDE theme. Pair with Themes.ActiveThemeName / Themes.ActiveThemeNameGroup to refresh any colour-sensitive elements the addin draws inside its tool windows.

Syntax: host_OnChangedTheme(ThemeName As String)

ThemeName: The new theme’s name — same value the user now sees in Themes.ActiveThemeName (e.g. "Classic", "Dark", "Light").

DebuggerEvaluateOptions

A flags enum declared inline on the Host interface; consumed by Project.Evaluate (and the future debugger-evaluation surface). Currently a single-value placeholder — additional flags may appear in later IDE versions.

Constant	Value	Description
NONE	0	No special evaluation options.