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VB Shell Programming by J.P. Hamilton

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Data Handler Interfaces

Data handlers implement two interfaces: IPersistFile andIDataObject. Everything that needs to be said about IPersistFile has already been said (see Section 5.2.1 in Chapter 5). Conversely, we know almost nothing about IDataObject. And even when we are done with this chapter, there will still be much that has not been said about this interface. The world of IDataObject is huge. It is one of the fundamental interfaces involved in OLE data transfers.

IDataObject

Table 8.1 shows all nine methods of IDataObject, but only three are required when writing data handlers in Visual Basic: QueryGetData, EnumFormatEtc, and GetData.

Table 8-1. The IDataObject Interface

Method

Description

GetData

Retrieves data from a data object, as defined by a FORMATETC structure. The data is then transferred through a STGMEDIUM structure.

GetDataHere

Similar to GetData except the caller is responsible for allocating and freeing all memory associated with FORMATETC and STGMEDIUM.

QueryGetData

Given a FORMATETC structure, this method determines if a resulting call to GetData will be successful.

GetCanonicalFormatEtc

Determines if two different FORMATETC structures would produce the same data, providing a means to eliminate a second call to GetData.

SetData

Allows another object to send data to the data object.

EnumFormatEtc

Provides a means to enumerate all the ways a data object can describe data in a FORMATETC structure.

DAdvise

Creates an event sink ...

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