Tutorial :Avoid doubling in combobox



Question:

I have following code that is generating random no. between 1 to 10. This is working fine. But, I do not want doubling in combobox (cmbRnd is my combo box). How can I avoid it?

Private Sub cmdRnd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles cmdRnd.Click      Dim random As New Random(), i As Integer = 1      Do While i < 10          cmbRnd.Items.Add(random.Next(1, 10))          i = i + 1      Loop  End Sub  


Solution:1

A better way is to generate an array of numbers 1â€"10 and then shuffle them.

The easiest way of shuffling numbers is sorting them randomly:

Dim rng As New Random()  Dim numbers As Integer() = Enumerable.Range(1, 10).OrderBy( _      Function(x) rng.Next()).ToArray()  

Next, please read why shuffling numbers like this is a bad idea! and how to do it better.

An unrelated remark:

Don’t use a While loop for iterating over numbers. This special use-case is better mapped by the For loop and people looking at your code will wonder for what reason the For loop was avoided. Consistency is sometimes a bit silly, but in such well-established cases there’s no reason to deviate from the norm.


Solution:2

Dim random As New Random(), i As Integer = 1  Dim cmbRnd As New Windows.Forms.ComboBox  Do While i < 10      Dim newItem As Int32 = random.Next(1, 10)      If Not cmbRnd.Items.Contains(newItem) Then          cmbRnd.Items.Add(newItem)          i = i + 1      End If  Loop  

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