Xojo can return arrays from method calls like
Function foo() as String()
Now what happens if you leave such a function without a return statement ?
Xojo will happily return a NIL array – not one that has no members but one that IS NIL
For instance, if you create the function as
Function foo() as string()
End Function
and then call it later like
dim arr() as string = foo
break
The debugger will show you that arr is NIL; not a valid array with no elements (some Xojo documentation conflates these two things but they are NOT the same)
If your code was
dim arr() as string = foo
arr.append "123"
You will get a NilObjectException (yes internally arrays are objects)
So how DO you check which it is ?
- use Is Nil to test if you got a NIL array
- use the count property if the array IS NOT NIL
dim arr() as string = foo
if arr is nil then
// ok now how do I deal with this ?
// how can I make it so I can add items ?
else if arr.count = 0 then
// ok we got back an array with no items in it
// appending items will work !
else
// ok we got back an array with items in it !
// appending items will work !
end if
Notice that if we get back a NIL we cant do much since there is NO array. Trying to append will raise an exception. So what can I do to make it NOT be a nil array ?
At first you might try the Redim function to create an array like
Redim arr(-1)
in API 2 this is arr.ResizeTo like arr.ResizeTo(-1) which will also fail
The right thing to do is use the Array FUNCTION to create one with some elements then resize it to 0 like
arr = Array("")
redim arr(-1)
The resulting code then looks like
dim arr() as string = foo
if arr is nil then
// ok got a NIL array
// but thanks to norm we know how to fix this
arr = Array("")
redim arr(-1)
else if arr.count = 0 then
// ok we got back an array with no items in it
// appending items will work !
else
// ok we got back an array with items in it !
// appending items will work !
end if
// and now here you can append items
// regardless of what the function gave you back
Have a great day
