IAssocHandler::Invoke method (shobjidl_core.h)

Article
10/13/2021

Directly invokes the associated handler.

Syntax

HRESULT Invoke(
  [in] IDataObject *pdo
);

Parameters

[in] pdo

Type: IDataObject*

A pointer to an IDataObject that represents the selected item on which to invoke the handler. Note that you should not call IAssocHandler::Invoke with a selection of multiple items. If you have multiple items, call IAssocHandler::CreateInvoker instead. See Remarks for more details.

Return value

Type: HRESULT

If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Remarks

IAssocHandler objects are typically used to populate an Open With menu. When one of those menu items is selected, this method is called to launch the chosen application.

Invoke and CreateInvoker

The IDataObject used by these methods can represent either a single file or a selection of multiple files. Not all applications support the multiple file option. The applications that do support that scenario might impose other restrictions, such as the number of files that can be opened simultaneously, or the acceptable combination of file types.

Therefore, an application often must determine whether the handler supports the selection before trying to invoke the handler. For example, an application might enable a menu item only if it has verified that the selection in question was supported by that handler.

It is generally safe to assume that an application will support invocation on a single item, and in those cases the application typically calls IAssocHandler::Invoke based on that assumption.

For multiple selection scenarios, however, the application should call IAssocHandler::CreateInvoker. That method retrieves an IAssocHandlerInvoker object that allows the calling application to first check whether the selection is supported (SupportsSelection), then to invoke the handler (Invoke).

IAssocHandler::Invoke can be called on a selection of multiple files, but it is not recommended because of the large processing load involved and no guarantee that it will succeed.

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 [desktop apps only]
Target Platform	Windows
Header	shobjidl_core.h (include Shobjidl.h)

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