Overriding OM GET() - Revision history

Krashan: Links++;

2011-01-26T08:21:32Z

Links++;

Krashan: Formatting.

2011-01-26T08:19:24Z

Formatting.

Krashan: Formatting.

2011-01-26T08:15:04Z

Formatting.

Krashan: Link to Polish translation.

2011-01-26T08:09:18Z

Link to Polish translation.

AusPPC at 06:05, 7 January 2011

2011-01-07T06:05:14Z

Krashan: Added a note of importance of returning TRUE for recognized attributes.

2011-01-05T21:20:15Z

Added a note of importance of returning TRUE for recognized attributes.

Krashan: Formatting.

2011-01-04T08:36:59Z

Formatting.

Krashan: More contents.

2011-01-04T08:36:40Z

Krashan: Contents added.

2011-01-04T08:25:51Z

Contents added.

Krashan: Added code.

2011-01-03T20:24:18Z

Added code.

New page

''Grzegorz Kraszewski''

IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)
{
switch (msg->opg_AttrID)
{
case Some_Integer_Tag:
*msg->opg_Storage = /* value of the tag */;
return TRUE;

case Some_String_Tag:
*(char**)msg->opg_Storage = "a fixed string value";
return TRUE;
}

return DoSuperMethodA(cl, obj, (Msg)msg);
}

@@ Line 13: / Line 13: @@
   };
-Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in the ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ''ULONG'', but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
+Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in the ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ''ULONG'', but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a [[Taglists|taglist]] iteration loop, its implementation is simple:
   IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)

@@ Line 13: / Line 13: @@
   };
-Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in the ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ULONG, but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
+Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in the ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ''ULONG'', but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
   IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)

← Older revision		Revision as of 08:15, 26 January 2011
Line 4:		Line 4:


−	The ''OM_GET()'' method, used for getting an attribute from an object, receives an opGet structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:	+	The ''OM_GET()'' method, used for getting an attribute from an object, receives an ''opGet'' structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:

	struct opGet		struct opGet

← Older revision		Revision as of 08:09, 26 January 2011
Line 1:		Line 1:
	''Grzegorz Kraszewski''		''Grzegorz Kraszewski''
		+	----
		+	<small>This article in other languages: [[Przeciążanie metody OM_GET()\|Polish]]</small>

@@ Line 2: / Line 2: @@
-The ''OM_GET()'' method, used for getting an attribute from an object, receives opGet structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:
+The ''OM_GET()'' method, used for getting an attribute from an object, receives an opGet structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:
   struct opGet
@@ Line 11: / Line 11: @@
   };
-Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ULONG, but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
+Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in the ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ULONG, but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
   IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)
@@ Line 29: / Line 29: @@
+  }
-The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized, the method should return ''TRUE''. It is very important, as [[Event Driven Programming, Notifications#Notifications in MUI|MUI notifications]] rely on OM_GET() and will not work on the attribute if ''TRUE'' is not returned. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as the ''default'' clause of the ''switch'' statement. It is important that ''msg->opg_Storage'' is '''deferenced''' when storing the attribute value. If the value type is not integer, a typecast is needed. For a value type ''T'', the deferention combined with typecast is denoted as ''*(T*)''.
+The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized, the method should return ''TRUE''. It is very important, as [[Event Driven Programming, Notifications#Notifications in MUI|MUI notifications]] rely on OM_GET() and will not work on the attribute if ''TRUE'' is not returned. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as the ''default'' clause of the ''switch'' statement. It is important that ''msg->opg_Storage'' is '''dereferenced''' when storing the attribute value. If the value type is not integer, a typecast is needed. For a value type ''T'', the dereferencing combined with typecast is denoted as ''*(T*)''.

← Older revision		Revision as of 21:20, 5 January 2011
Line 29:		Line 29:
	}		}

−	The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized, the method should return ''TRUE''. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as the ''default'' clause of the ''switch'' statement. It is important that ''msg->opg_Storage'' is '''deferenced''' when storing the attribute value. If the value type is not integer, a typecast is needed. For a value type ''T'', the deferention combined with typecast is denoted as ''(T)''.	+	The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized, the method should return ''TRUE''. It is very important, as [[Event Driven Programming, Notifications#Notifications in MUI\|MUI notifications]] rely on OM_GET() and will not work on the attribute if ''TRUE'' is not returned. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as the ''default'' clause of the ''switch'' statement. It is important that ''msg->opg_Storage'' is '''deferenced''' when storing the attribute value. If the value type is not integer, a typecast is needed. For a value type ''T'', the deferention combined with typecast is denoted as ''(T)''.

← Older revision		Revision as of 08:36, 4 January 2011
Line 1:		Line 1:
	''Grzegorz Kraszewski''		''Grzegorz Kraszewski''
		+

	The ''OM_GET()'' method, used for getting an attribute from an object, receives opGet structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:		The ''OM_GET()'' method, used for getting an attribute from an object, receives opGet structure as its message. The structure is defined in the ''<intuition/classusr.h>'' header file:

@@ Line 10: / Line 10: @@
   };
-Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ULONG, but it may point to anything (for example some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simpler:
+Unlike ''[[Overriding OM_SET()|OM_SET()]]'', this method handles only one attribute at a time. The attribute is placed in ''opg_AttrID'' field. The field ''opg_Storage'' is a '''pointer''' to a place where the attribute value should be stored. It is defined as a pointer to ULONG, but it may point to anything (for example to some larger structure). It allows for passing attributes not fitting in a 32-bit variable. Because ''OM_GET()'' does not have a taglist iteration loop, its implementation is simple:
   IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)
@@ Line 28: / Line 28: @@
+  }
-The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized the method should return ''TRUE''. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as a ''default'' clause of
+The implementation consists of a ''switch'' statement with ''cases'' for all recognized attributes. If an attribute is recognized, the method should return ''TRUE''. Unknown attributes are passed to the superclass. The ''DoSuperMethodA()'' call may be alternatively placed as the ''default'' clause of the ''switch'' statement. It is important that ''msg->opg_Storage'' is '''deferenced''' when storing the attribute value. If the value type is not integer, a typecast is needed. For a value type ''T'', the deferention combined with typecast is denoted as ''*(T*)''.

@@ Line 1: / Line 1: @@
 ''Grzegorz Kraszewski''
   IPTR MyClassGet(Class *cl, Object *obj, struct opGet *msg)
@@ Line 18: / Line 27: @@
     return DoSuperMethodA(cl, obj, (Msg)msg);
+  }