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Resolved ClassName() Null object reference

  1. How-to
0
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  1. Tomas Beran
    Tomas Beran
  2. PowerBuilder
  3. Thursday, 31 August 2023 18:39 PM UTC

PB2022 R2 2819, this code:

window lw_wnd

string ls_classname

if ( IsNULL( lw_window )) then return

ls_classname = ClassName( lw_window )

 

triggers "Null object reference" at line 4 exception.

Is this correct and expected behavior? Or is it something new in PB2022?

Is there anybody who could check it in PB2021 or older?

Thank you

PBSHR.dll 0x0008ed1e
Power-Client -
Responses (3)
Tomas Beran
Tomas Beran Accepted Answer Pending Moderation
  1. Friday, 1 September 2023 11:57 AM UTC
  2. PowerBuilder
  3. # 1

Thank you for testing. So this behavior wasn't been changed in PB2022.

 

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Arnd Schmidt
Arnd Schmidt Accepted Answer Pending Moderation
  1. Thursday, 31 August 2023 19:23 PM UTC
  2. PowerBuilder
  3. # 2

Expected. Same in PB 10.5.

Use IsValid() to check if the window is valid.

window lw_window

string ls_classname

if IsValid( lw_window ) then
   ls_classname = ClassName( lw_window )
else
   return
end if

 

hth

Arnd

Comment
Chris Pollach @Appeon
  1. Chris Pollach @Appeon
  2. Thursday, 31 August 2023 20:26 PM UTC
Hi Arnd;

Yes, IsValid should be used and NOT IsNull for that validation check! ;-)

Regards ... Chris
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Francisco Martinez @Appeon
Francisco Martinez @Appeon Accepted Answer Pending Moderation
  1. Thursday, 31 August 2023 19:21 PM UTC
  2. PowerBuilder
  3. # 3

What happens if you use not IsValid(...) instead of IsNull(...)?

AFAIK IsNull(...) checks that the variable contains the explicitly-assigned value NULL. When a variable is declared but not initialized, it's not NULL, it's... uninitialized.

Regards,
Francisco

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