CODEWITHSUNDEEP
vb.netvisual-studio-2012
dranreb dino
dranreb dino

Reputation: 260

pass parameter from loop value to dynamic function

I am making loop to make an array of Timers and give each timer a function

here's something like what i did:

dim timer(10) as Timer
for i = 0 to 5
timer(i) = new Timer
AddHandler timer(i).Tick, Function(senderX, eX) timerFunction(i)
next

i have this function:

Private Function timerFunction(ByVal timerNo As Integer)
    MsgBox(timerNo)
End Function

but i am getting 6 as the value of timerNo for every timer i call with this:

timer(3).Start()

i outputs 6 even in i change the parameter to a number from 1 to 5

why is it diong that?

Upvotes: 0

Views: 486

Answers (1)

SSS
SSS

Reputation: 5393

You have "closed over the loop variable". The value of timerNo is evaluated at the time the function is called which is always after the loop has completed, so the value of timerNo will always be 6.

You should have got a compiler warning: "BC42324 Using the iteration variable in a lambda expression may have unexpected results. Instead, create a local variable within the loop and assign it the value of the iteration variable."

To do this with your example...

Dim timer(10) As Timer
For i As Integer = 0 To 5
  Dim j As Integer = i
  timer(i) = New Timer
  timer(i).Interval = 1000
  timer(i).Enabled = True
  AddHandler timer(i).Tick, Function(senderX, eX) timerFunction(j)
Next

Function timerFunction(timerNo As Integer) As String
  MsgBox(timerNo)
  Return timerNo.ToString
End Function

This way, a new instance of j is created for each iteration of the loop.

Upvotes: 1

Related Questions