Cannot change array element in collection
Hey
I found today that apparently one cannot change an array element's value if that array is stored in a collection. The only way to change it is to remove the array from the collection and replace it with a different one.
Is this true, or have I lost it?
Code:
Dim c As Collection
Dim a(0 To 1) As String
Dim b(0 To 1) As String
Set c = New Collection
a(0) = "foo"
a(1) = "123"
c.Add a, "key1"
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
c("key1")(0) = "bar"
c("key1")(1) = "789"
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
b(0) = "bar"
b(1) = "789"
c.Add "", "REPLACE", "key1"
c.Remove "key1"
c.Add b, "key1", , "REPLACE"
c.Remove "REPLACE"
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
And the output:
Code:
0: foo
1: 123
0: foo
1: 123
0: bar
1: 789
Re: Cannot change array element in collection
Quote:
Originally Posted by
OldClock
I found today that apparently one cannot change an array element's value if that array is stored in a collection.
That's problem #1 - but it can be solved by changing to Collection-Replacements, which allow changing Elements directly
(without a Remove->Re-Add sequence).
Quote:
Originally Posted by
OldClock
The only way to change it is to remove the array from the collection and replace it with a different one.
Is this true, or have I lost it?
That's a (slightly different) problem #2...
An Array in VB is implemented as a SafeArray - being a "Pointer-Type" (like a String).
So, assuming you have already switched to a Collection which supports changing Elements directly,
you still cannot do something like:
Code:
Col(i)(k) = New_ArrayValue_For_Index_k
Instead you will have to retrieve the whole Array, change stuff in it - and set it back into the Index-Position i in the Col.:
Code:
Col(i) = Replace_ArrayValue_Inside( Col(i) )
Function Replace_ArrayValue_Inside( Arr() As SomeType ) As SomeType()
Arr(k) = NewValue
Replace_ArrayValue_Inside = Arr 'return the changed result from the helper-function
End Function
Same thing with Strings (in case you assume for a moment, that "String" is just another name for "Array of Chars")
Code:
Col(i) = Replace_StringValue_Inside( Col(i) )
Function Replace_StringValue_Inside( S As String ) As String
Replace_StringValue_Inside = Replace(S, "OldChars", "NewChars")
End Function
To achieve what you want, you will have to switch to Object-Encapsulations of Arrays or Strings.
E.g. the following works with
- the RC5-cCollection (a VB-compatible Collection-replacement, which allows direct Item-Changes)
- the RC5-cArrayList (a wrapper around differently typeable, single-dimension-arrays)
Code:
Private Sub Form_Load()
Dim Col As cCollection
Set Col = New_c.Collection
'add a ByteArray to the Collection (with 3 Byte-Value-Members)
Col.Add New_c.ArrayList(vbByte, 1, 2, 3)
'Print the current Array-content at the (OneBased) Collection-Index 1
Debug.Print Col(1).Join(",") '... will print out: 1,2,3
'since the ByteArray is wrapped behind an Object, you can now directly change the first Array-Member (at Idx 0)
Col(1)(0) = 111
'Print the current Array-content again
Debug.Print Col(1).Join(",") '... will print out: 111,2,3
End Sub
HTH
Olaf
Re: Cannot change array element in collection
Another option could be to use a class that holds your array, similar to what Olaf was describing as "Object-Encapsulations"
Class. We'll name this clsArray
Code:
Private myArray() As String ' variant, long, integer, etc
Public Sub SizeArray(lowerBound As Long, upperBound As Long, Optional bPreserve as Boolean = False)
If bPreserve Then
ReDim Preserve myArray(lowerBound to upperBound)
Else
ReDim myArray(lowerBound to upperBound)
End If
End Sub
Public Property Get Item(Index As Long) As String ' variant, long, integer, etc
Item = myArray(Index)
End Property
Public Property Let Item(Index As Long, Value As String)
myArray(Index) = Value
End Property
Public Property Get LowerBound() As Long
LowerBound = LBound(myArray)
End Property
Public Property Get UpperBound() As Long
UpperBound = UBound(myArray)
End Property
now using your example:
Code:
Dim c As Collection, a As ClsArray
Set a = New ClsArray
a.SizeArray 0, 1
Set c = New Collection
a.Item(0) = "foo"
a.Item(1) = "123"
c.Add a, "key1"
Debug.Print "0: " & c("key1").Item(0)
Debug.Print "1: " & c("key1").Item(1)
c("key1").Item(0) = "bar"
c("key1").Item(1) = "789"
Debug.Print "0: " & c("key1").Item(0)
Debug.Print "1: " & c("key1").Item(1)
Re: Cannot change array element in collection
Thank you for the replies!
Schmidt by "Collection-Replacements" and RC5 do you mean this?
http://vbrichclient.com/
What you wrote here in the forum has me interested, but:
- there is no page clearly explaining what vbRichClient is (in simple terms, i.e. it doesn't sell itself), what it can do for me, which Windows versions it runs on and which it has issues with, whether it runs in Wine as VB6 classic can,
- it does not state what licence the code is under, or whether it is in the public domain,
- the "about" text on that site states that the framework will be completed in "another 1.5-2 years or so" and that was written in 2013,
- many pages have "no content yet...",
- there is no documentation,
Those point are quite discouraging from investing time in digging into it - would be great if you could clarify.
LaVolpe interesting solution!
Re: Cannot change array element in collection
Hi OldClock, I've been a happy user of the vbRichClient5 library (and it's earlier dhRichClient incarnations) for over a decade. The web-site doesn't do it justice!
RC5 (as I'll shorten vbRichClient5) is an framework/library intended to modernize your VB6 applications. It is completely free to use and distribute, but is not open source.
Some of the features it includes:
- Graphical enhancements (PNG, alpha/transparency support, etc...) by way of a wrapper for the open source Cairo library.
- A fast, powerful, self-contained database support via a wrapper for the public domain SQLite.
- The ability to perform remote procedure calls (RPC) over a network (client-server apps).
- All manner of helpful, powerful, and high-performance classes for things like the cCollection class he introduced you to in this thread. Others include an ArrayList class, FSO replacement, encryption & hash functions, etc...
There's a lot more too. Here's some projects & demos that use the library that might interest you:
There are a lot more demos to be found here: Click Here for Search Results.
Anyway, I recommend giving it a try - it certainly won't hurt!
Re: Cannot change array element in collection
@OldClock, just fyi...
If you use the class method, you can set the default property of the class to the Item property. Doing so allows you to exclude the Item term in the sample code to be more like your original example. So...
Instead of: c("key1").Item(0) = "bar"
changed to: c("key1")(0) = "bar"
Re: Cannot change array element in collection
LaVolpe I change your idea to something else:
item must be the default property
Code:
Private myArray() ' variant, long, integer, etc
Public Sub SizeArray(LowerBound As Long, UpperBound As Long, Optional bPreserve As Boolean = False)
If bPreserve Then
ReDim Preserve myArray(LowerBound To UpperBound)
Else
ReDim myArray(LowerBound To UpperBound)
End If
End Sub
Public Property Get Item(Optional Index As Variant) As Variant ' variant, long, integer, etc
Dim m As ClsArray
If IsMissing(Index) Then
Item = myArray()
ElseIf IsNumeric(Index) Then
Item = myArray(Index)
Else ' not used here........If TypeName(Index) = "Variant()" Then
Set m = New ClsArray
m() = Index
Item = m()
End If
End Property
Public Property Let Item(Optional Index As Variant, Value As Variant)
If IsMissing(Index) Then
myArray() = Value
Else
myArray(Index) = Value
End If
End Property
Public Property Get LowerBound() As Long
LowerBound = LBound(myArray)
End Property
Public Property Get UpperBound() As Long
UpperBound = UBound(myArray)
End Property
So now we have this code working
Code:
Sub test()
Dim c As Collection, a As ClsArray
Set a = New ClsArray
Set c = New Collection
a() = Array("foo", "123")
c.Add a, "key1"
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
c("key1") = a(Array("bar", "789"))
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
c("key1") = a(Array("alfa", "beta"))
Debug.Print "0: " & c("key1")(0)
Debug.Print "1: " & c("key1")(1)
Debug.Print c("key1").UpperBound
c("key1") = a(Array(a(Array("foo", "123")), a(Array("alfa", "beta"))))
Debug.Print "0: " & c("key1")(0)(0)
Debug.Print "1: " & c("key1")(1)(1)
End Sub
