Guide to Using Checkboxes

[aburningflame]

This is in response to the whole 'how do i check if a checkbox is true' question.
THe problem people have is they compare against the wrong type (ive done it myself).

You would EXPECT a checkbox to return an L type - but I think there are certain events or times where it doesnt.
Sometimes it returns "1" or "true" instead of .t. and "0"/"false" instead of .f.

This makes the comparison fieldname==.t. lead to unexpected results in certain events/cases.

So here you go world:

This isn't a very understandable "guide to using check boxes"

Here is my guide. I use checkboxes no problem.

FieldName: active
Control Type:Checkbox
Treat as Logical Field: Checked

In other fields:
Show hide Expression: active=0or1
Enable Expression: active=0or1

Comparison in Xbasic:
convert_type(active,"L")==.t. <<Force a convert to L type (Failure to convert to L results in 0 which makes this statement false)
convert_type(active,"N")==1 <<If the above fails (which it shouldnt, you can convert to N and compare against N)

THe problem most people have is they're comparing against the wrong type
for example:

IF active==1 'if active is an L type, this may not evaluate properly
IF active==.t. 'if active is a C type, this may not evaluate properly

Using convert_type(active,"L") converts it to type L (boolean).
So, you compare the converted type L to .t.|.f. (boolean operators)


Interactive Window Mumbo Jumbo:

?convert_Type(1,"L")
= .T.

?convert_Type(0,"L")
= .F.

?convert_type("true","L")
= .T.

?convert_type("false","L")
= .F.

?convert_type(.t.,"L")
= .T.

?convert_type(.f.,"L")
= .F.

COMPARISONS
?"true"==.t.      CORRECT BUT MISUNDERSTOOD RETURN BECAUSE OF COMPARING 2 DIFFERENT TYPES
= .F.

?convert_type("true","L")==.t.  CORRECT
= .T.

?"false"==.t.   CORRECT BUT MISUNDERSTOOD RETURN BECAUSE OF COMPARING 2 DIFFERENT TYPES
= .F.

?convert_type("false","L")==.t. CORRECT
= .F.

?1==.t. CORRECT BUT MISUNDERSTOOD RETURN BECAUSE OF COMPARING 2 DIFFERENT TYPES
= .F.

?convert_type(1,"L")==.t. CORRECT
= .T.


?0==.t.
= .F.

?convert_type(0,"L")==.t.
= .F.

FINAL EXAMPLE: APPLES TO ORANGES
dim myfield as C="true"
?typeof(myfield)
= "C"
?typeof(.t.)
= "L"
?myfield==.t.  'C to L comparison - WRONG!
= .F.
?typeof(convert_type(myfield,"L"))
= "L"
?convert_type(myfield,"L")==.t.
= .T.

Moral of the story, dont compare apples to oranges.
If you are comparing x against y make sure they're the same type and you wont get unexpected results.