Hacker’s Guide to Visual FoxPro
An irreverent look at how Visual FoxPro really works. Tells you the inside scoop on every command, function, property, event and method of Visual FoxPro.
Sys(1269)
SYS(1269) returns information about an object’s properties. It provides two pieces of information about each—whether it’s been changed from the default and whether it’s read-only. Broken in VFP 3.0, it has been superseded in later versions by the preferable PEMStatus().
Usage
lPropertyHasAttribute = SYS( 1269, oObject, cProperty,
nAttribute )
|
Parameter |
Value |
Meaning |
|
oObject |
Object |
The object whose properties are to be checked. |
|
cProperty |
Character |
The name of the property to check. |
|
nAttribute |
0 |
Has the property changed from its default value? |
|
1 |
Is the property read-only? |
SYS(1269) was a very late addition to VFP 3; in fact, it was added to the product so late that it didn’t get into the docs. It didn’t work so well in that version, either, but by 3.0b was performing as advertised. However, by that point, the facilities it offered were so clearly needed that they got incorporated in a real, mnemonically (well, almost mnemonically) named function—PEMStatus(). So, in practice, there’s never any reason to use SYS(1269), except in VFP 3.0, where it doesn’t work right. (Specifically, in that version, passing 1 for nAttribute always returns .F., whether or not the property is read-only.)
|
When you pass 0 for nAttribute, SYS(1269) returns .T. only if the property has changed by being explicitly set. For example, if you add an object to a form, so ControlCount changes from 0 to 1, SYS(1269, oForm, "ControlCount", 0) returns .F., not .T. as we'd expect. It's possible, though, that it's meant to reflect only changes due to direct assignments. Similarly, SYS(1269) returns .F. when a property was changed in the class on which the object is based, but not in this instance of the object. |
Example
oForm = CreateObject('Form')
? SYS(1269, oForm, "Left", 0) && Returns .F.
oForm.Left = 50
? SYS(1269, oForm, "Left", 0) && Returns .T.
? SYS(1269, oForm, "BaseClass", 1) && Returns .T.
&& except in VFP 3.0