ArcObjects Library Reference  (Controls)    

HookHelper CoClass

Helps commands work with the MapControl, PageLayoutControl, ArcMap, custom controls and applications.

Product Availability

Available with ArcGIS Engine.


The HookHelper is designed to help developers write custom commands that will work with some ArcGIS Engine Controls and applications.

When creating a custom command the ICommand::OnCreate event is passed a hook to the control or application that the command will work with. The command needs to determine the type of hook that is passed so it knows how to handle itself. Rather than adding code into the ICommand::OnCreate event to determine the type of hook a HookHelper object can do this. The HookHelper is used to hold the hook and return the IActiveView, PageLayout or FocusMap regardless of whether the hook is a MapControl, PageLayoutControl, ToolbarControl (with a 'buddy' MapControl or PageLayoutControl), the ArcMap application or a custom control or application implementing ICommandHook.

When using the HookHelper in the ICommand::OnCreate event of custom commands the following must be considered:

Extended Error Information

Use the ISupportErrorInfo method InterfaceSupportsErrorInfo to determine if the object supports extended error information. If the object supports extended error info, VC++ developers should use the OLE/COM IErrorInfo interface to access the ErrorInfo object. Visual Basic developers should use the global error object Err to retrieve this extended error information.


Interfaces Description
IConnectionPointContainer Supports connection points for connectable objects.
IHookActions Provides access to actions such as flashing, panning and zooming that help in the development of commands to work with controls, custom controls and applications.
IHookHelper Provides access to members needed when developing commands to work with the MapControl, PageLayoutControl, ArcMap, and custom controls and applications.
ISupportErrorInfo Indicates whether a specific interface can return Automation error objects.

Event Interfaces

Interfaces Description
IHookHelperEvents (default) Provides access to events that occur when the state of a hook changes.

Working with Events

[Visual Basic 6.0]

When working with HookHelper's default outbound interface in Visual Basic 6 declare variables as follows:

Private WithEvents pHookHelper as HookHelper