Null check in VB

Question

All I want to do is check if an object is null  but no matter what I do  if it compiles  it throws a NullReferenceException just trying to check  Here s what I ve done       If   Not  comp Container Is Nothing   And  Not  comp Container Components Is Nothing    Then         For i As Integer   0 To comp Container Components Count   - 1 Step 1             fixUIIn comp Container Components Item i   style          Next     End If      If   Not IsDBNull comp Container   And  Not IsDBNull comp Container Components    Then         For i As Integer   0 To comp Container Components Count   - 1 Step 1             fixUIIn comp Container Components Item i   style          Next     End If      If   Not IsNothing comp Container   And  Not IsNothing comp Container Components    Then         For i As Integer   0 To comp Container Components Count   - 1 Step 1             fixUIIn comp Container Components Item i   style          Next     End If      If   Not  comp Container Is DBNull Value   And  Not  comp Container Components Is DBNull Value    Then         For i As Integer   0 To comp Container Components Count   Step 1             fixUIIn comp Container Components Item i   style          Next     End If   I ve looked through VB books  searched several forums  and everything that SHOULD work doesn t  Sorry for asking such a remedial question  but I just need to know   Just so you know  the debugger says that the null object is comp Container

User · Accepted Answer

Change your Ands to AndAlsos A standard And will test both expressions   If comp Container is Nothing  then the second expression will raise a NullReferenceException because you re accessing a property on a null object  AndAlso will short-circuit the logical evaluation   If comp Container is Nothing  then the 2nd expression will not be evaluated

User · Answer

Your code is way more cluttered than necessary   Replace  Not  X Is Nothing   with X IsNot Nothing and omit the outer parentheses   If comp Container IsNot Nothing AndAlso comp Container Components IsNot Nothing Then     For i As Integer   0 To comp Container Components Count   - 1         fixUIIn comp Container Components i   style      Next End If   Much more readable       Also notice that I   ve removed the redundant Step 1 and the probably redundant  Item   But  as pointed out in the comments   index-based loops are out of vogue anyway  Don   t use them unless you absolutely have to  Use For Each instead   If comp Container IsNot Nothing AndAlso comp Container Components IsNot Nothing Then     For Each component In comp Container Components         fixUIIn component  style      Next End If

[vb.net] Null check in VB

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