OLEDISPPARAMS type

The arguments of a call through IDispatch.Invoke, with the layout of the Windows DISPPARAMS structure.

OLEDISPPARAMS is a user-defined type declared in the package’s OLEGuids module, so both OLEDISPPARAMS and OLEGuids.OLEDISPPARAMS name it. It mirrors the Windows structure DISPPARAMS, which holds the addresses and the counts of the arguments and of the named arguments of a call.

Public Type OLEDISPPARAMS
    rgvarg As LongPtr
    rgdispidNamedArgs As LongPtr
    cArgs As Long
    cNamedArgs As Long
End Type

Fields

rgvarg

A LongPtr holding the address of an array of Variant values, which are the arguments. They are in reverse order: element 0 is the last argument of the call and the highest element is the first. The named arguments come first in the array, so they are the last of the call’s own order.

rgdispidNamedArgs

A LongPtr holding the address of an array of Long values, which are the dispatch identifiers of the named arguments, in the order of the first cNamedArgs elements of rgvarg. It is 0 when there are no named arguments.

cArgs

A Long holding the number of elements in rgvarg, the named arguments included.

cNamedArgs

A Long holding the number of elements in rgdispidNamedArgs.

A variable that is not filled in holds only zeros, which is a call with no arguments.

An assignment to a property passes the new value as the only argument, named with the reserved identifier DISPID_PROPERTYPUT (-3): cArgs and cNamedArgs are 1, and rgdispidNamedArgs is the address of a Long holding -3. The IDispatch page in the COM Interfaces section describes the structure further.

Where it is used

IDispatchUnrestricted.Invoke takes the address of an OLEDISPPARAMS variable, from VarPtr, as lpdispparams. No method of the package takes the structure by name.

Example

This procedure assigns 25 to the Level property of a Gauge object by its dispatch identifier, through Invoke with the access flag 4 (DISPATCH_PROPERTYPUT).

Dim g As New Gauge
Dim d As IDispatchUnrestricted = g

Dim iid As OLECLSID
Dim namePtr As LongPtr = StrPtr("Level")
Dim id As Long
d.GetIDsOfNames iid, namePtr, 1, 0, id

Dim newValue(0 To 0) As Variant
newValue(0) = 25
Dim putId As Long = -3  ' DISPID_PROPERTYPUT
Dim params As OLEDISPPARAMS
params.rgvarg = VarPtr(newValue(0))
params.rgdispidNamedArgs = VarPtr(putId)
params.cArgs = 1
params.cNamedArgs = 1

Dim argErr As Long
d.Invoke id, iid, 0, 4, VarPtr(params), 0, 0, argErr
Debug.Print g.Level  ' 25

See Also

• IDispatchUnrestricted interface – finds and calls members of an automation object by name or dispatch identifier
• OLECLSID type – a class or interface identifier