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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
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Use the IsNull function to determine whether an expression contains a Null value. Expressions that you might expect to evaluate to True under some circumstances, such as If Var = Null and If Var <> Null , are always False. This is because any expression containing a Null is itself Null and therefore False.
A null indicates that a variable doesn't point to any object and holds no value. You can use a basic 'if' statement to check a null in a piece of code. Null is commonly used to denote or verify the non-existence of something.
When checking whether a reference (or nullable value type) variable is null , do not use = Nothing or <> Nothing . Always use Is Nothing or IsNot Nothing . For strings in Visual Basic, the empty string equals Nothing . Therefore, "" = Nothing is true.
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.
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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 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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