CODEWITHSUNDEEP
vb.netfor-loopdictionaryarraylist
babboon
babboon

Reputation: 793

vb.net arraylist dictionary loop

What I did here is save table of two columns in a arraylist and dictionary. 

Dim result As New ArrayList()
While dr.Read()
        ' Insert each column into a dictionary
        Dim dict As New Dictionary(Of String, Object)
        For count As Integer = 0 To (dr.FieldCount - 1)
            dict.Add(dr.GetName(count), dr(count))
        Next
        ' Add the dictionary to the ArrayList
        result.Add(dict)
    End While

......... Now I want to go through it and when it found - remove it. Its for time saving as there are lots of data. I get error "Collection was modified; enumeration operation may not execute." after removal and going to next. I understand the problem but how do I overcome this? How to convert it to loop with removal? 

For Each dat As Dictionary(Of String, Object) In result 
                        comp2 = dat("ID") 
                        If comp2 = comp Then
                            advcode = advcode & "," & dat("ADVC")
                            found = True
                            firstattempt = False
                            result.Remove(dat)
                        Else
                            If found And Not firstattempt Then Exit For
                        End If
                    Next

Upvotes: 1

Views: 3490

Answers (3)

SysDragon
SysDragon

Reputation: 9888

Try this:

Dim iCont As Integer = 0

While result.Count > iCont
    Dim dat As Dictionary(Of String, Object) = CType(result(iCont), Dictionary(Of String, Object))
    comp2 = dat("ID") 
    If comp2 = comp Then
        advcode = advcode & "," & dat("ADVC")
        found = True
        firstattempt = False
        result.Remove(dat)
    Else
        If found And Not firstattempt Then Exit For
        iCont += 1
    End If   
End While

Upvotes: 1

Rex
Rex

Reputation: 2140

normally two ways to fix it:

  1. traverse the arraylist from the back:

    For i As Integer = result.Count - 1 To 0 Step -1
    Dim dat = CType(result(i), Dictionary(Of String, Object))
    ' ...
    ' if found:
    result.RemoveAt(i)
Next

  2. copy the arraylist to a new array:

    For Each Dat As Dictionary(Of String, Object) In result.ToArray()
    ' do your stuff here
Next

option 1 should give better performance

Upvotes: 1

sloth
sloth

Reputation: 101142

Why don't you use a List(Of Dictionary(Of String, Object)) instead of an ArrayList? That would make the code clearer.

Nonetheless, just copy the collection into a new one, so removing an element from the original collection does not stop the iteration of the copy:

For Each dat As Dictionary(Of String, Object) In result.ToArray() ' Copy into new array '
    comp2 = dat("ID") 
    If comp2 = comp Then
        advcode = advcode & "," & dat("ADVC")
        found = True
        firstattempt = False
        result.Remove(dat)
    Else
        If found And Not firstattempt Then Exit For
    End If
Next

Upvotes: 2

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