Programmer Reference : Object Linking and Embedding (OLE) : Using OLE custom controls (OCXs) : Implementing an ambient-property handler
Implementing an ambient-property handler
Ambient properties are used by a container to give an OCX information about its surroundings, such as the background color of a form, the current font, or the locale ID of the container's user interface.
Each ambient property is identified by a unique DISPID, which an OCX uses to specify which ambient property it wants from its container. To support the integration of OCXs with containers, OLE defines a set of standard ambient-property DISPIDs. This set is encoded into the Smalltalk pool dictionary PlatformConstants as follows:
Ambient Property DISPID
Class
Specifies
DispidAmbientBackcolor
Integer
The color of the interior of an OCX (in RGB values)
DispidAmbientDisplayname
String
the name the OCX should display for itself in error messages
DispidAmbientDisplayasdefault
Boolean
Whether a button OCX should draw itself with a thicker frame (for button-like OCXs only)
DispidAmbientForecolor
Integer
The color of the display of text and graphics in an OCX (in RGB values)
DispidAmbientLocaleid
Integer
The ID of the UI locale
DispidAmbientMessagereflect
Boolean
Whether the container wants to receive MS Windows messages
DispidAmbientSupportsmnemonics
Boolean
Whether the container processes mnemonics
DispidAmbientShowgrabhandles
Boolean
Whether the OCX should show grab handles when in-place activated
DispidAmbientShowhatching
Boolean
Whether an OCX should show a hatch border when in-place activated
DispidAmbientScaleunits
String
The name of the units by the container
DispidAmbientTextalign
Integer
How text should be aligned in an OCX:
0
General (numbers to the right, text to the left)
1
Left
2
Center
3
Right
4
Fully justified
DispidAmbientUsermode
Boolean
Whether the container is in design mode (false) or run mode (true)
DispidAmbientUidead
Boolean
Whether the container is in a mode in which OCXs should ignore user input
Ambient-property handlers are implemented as methods that take a single parameter, which is the DISPID of the ambient property being requested by the OCX. OCXs may not request all possible ambient properties but only those they are interested in. Likewise, a container may not necessarily be able to respond to all ambient property requests. The ambient property handler answers the value of the requested property if it can; otherwise, it answers a nil value to inform the OCX that the property is not available. For example, the ambient-property-handler method dispidAmbientPropertyAt: in the above example might be implemented as follows:
dispidAmbientPropertyAt: dispid
"Private - Handle ambient properties."
DispidAmbientShowgrabhandles == dispid ifTrue: ^false].
DispidAmbientShowhatching == dispid ifTrue: ^false].
DispidAmbientLocaleid == dispid ifTrue: ^LocaleUserDefault].
DispidAmbientUidead == dispid ifTrue: ^false].
DispidAmbientUsermode == dispid ifTrue: ^false].
^nil
Here, the constant LocaleUserDefault comes from the pool dictionary PlatformConstants.
Note:
A class that implements OLE-container behavior should declare PlatformConstants as pool dictionaries.
Last modified date: 01/29/2015