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An OLE custom control is a reusable software component designed to run inside a host application. In current Microsoft terminology, the closest equivalent is an ActiveX control: a COM-based component that uses OLE functionality. Depending on the control and host, it may display an interface, expose properties and methods, raise events, and save its state. Microsoft classifies ActiveX as legacy technology and advises against using it for new development.
What does “OLE custom control” mean?
“OLE custom control” is a historical or informal name for a programmable component that participates in OLE hosting. Microsoft’s current documentation describes the related ActiveX control model rather than treating “OLE custom control” as a separate modern technology.
An ActiveX control is a reusable component built on the Component Object Model (COM). A host application—often called a control container—can embed it and interact with the capabilities it provides. The control might be a button or a more specialized component for tasks such as database access, data monitoring, or graphing. These are examples, not features guaranteed in every control. Microsoft Learn describes ActiveX controls as reusable COM components that support OLE functionality.
How does an OLE custom control work with its host?
The container and control cooperate. The container positions and displays the control, supports relevant user interaction, and can call the control’s methods or change its properties. The control may notify the container by raising events. Exactly which interactions are available depends on what both the control and container implement.
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Interfaces and optional capabilities
Microsoft’s control-container guidelines identify IUnknown as the minimum interface for an ActiveX control. Other interfaces and features are optional, and containers vary in what they support. A container should use QueryInterface to check whether a control provides a particular interface before relying on it. If a needed capability is unavailable, the application should handle that case rather than assume every control behaves alike. Microsoft’s guidelines explain interface checking and container variability.
Properties, methods, events, and display
A control can expose properties that the host reads or sets, methods that the host invokes, and events that report something the control has detected. It may also draw a visual interface inside the host. These capabilities are not universal; confirm what a particular control supports and what its container recognizes. Microsoft’s ActiveX controls architecture documentation describes these parts of the control-and-container model.
Persistence
Persistence is the ability to save control state, such as property values, so an embedded control can be recreated with that state. The container provides or manages access to persistent storage; the control does not independently select or obtain the host’s storage medium. Microsoft Learn’s MFC documentation discusses persistence among ActiveX control capabilities.
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Is an OCX the same as an ActiveX control?
Not exactly. “ActiveX control” describes a component model and its role; .ocx is a file extension associated with certain control files. Microsoft’s Excel support documentation also describes registering an ActiveX control file with an .ocx or .dll extension. The extension alone does not establish that a file is an ActiveX control, compatible with a particular host, safe, or supported.
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Microsoft provides a specific Excel workflow for adding or registering an ActiveX control. Treat that as an application-specific procedure, not as a general reason to register an unfamiliar file.
Is ActiveX still supported?
ActiveX remains relevant when maintaining some existing Windows software, but Microsoft labels it legacy technology and says it should not be used for new development. Support also depends on the application and platform, so a control that worked in one environment may not be available in another.
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- Windows desktop Office: Microsoft says ActiveX controls are disabled by default in desktop versions of Excel, Word, PowerPoint, and Visio in Microsoft 365 and Office 2016 or later.
- Office for Mac and Office on the web: Microsoft says these platforms do not support ActiveX controls.
- New Office solutions: Microsoft points to Form Controls, Office Add-ins, or other modern features as alternatives. The suitable choice depends on what the solution needs to do.
These statements apply to the Office products and platforms Microsoft identifies; they do not establish the support status of every Windows application or ActiveX container. See Microsoft’s ActiveX support and registration guidance for the Office-specific details, and Microsoft Learn’s MFC documentation for the legacy warning.
What should you check before using an existing control?
- Host and platform: Confirm that the target application and operating system support the control, including any relevant security defaults.
- Required interfaces: Identify which COM interfaces and component capabilities the control needs, then verify that the container supports them.
- Actual behavior: Check the properties, methods, events, display behavior, and persistence features the control implements; do not infer them from the term “OLE control” or a file extension.
- Alternative approach: For new work, determine whether a supported modern feature can meet the same need instead of adopting a legacy ActiveX dependency.
Microsoft’s model is described across its MFC ActiveX overview, control-container guidelines, and ActiveX architecture documentation.
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