如何将3个列表框项目添加到一个列表框中

Question

I'm using vb.net form.

I have 3 listboxes each one contains many items (listbox1 , listbox2,listbox3) and another empty listbox (listbox4) im trying to add first three listboxes items into the 4th listbox

ex: ) listbox1 first items is 'A' , listbox2 first items is 'b' , listbox3 first items is 'c' now listbox4 first item must be "Abc"

The problem is I't's work but keep loop the items. here is my code :

For i = 1 To ListBox1.Items.Count - 1

       For j = i To ListBox2.Items.Count - 1

           For k = j To ListBox3.Items.Count - 1

               ListBox4.Items.Add(ListBox1.Items(j).ToString + ListBox2.Items(j).ToString + ListBox3.Items(k).ToString)

               Exit For
           Next
       Next
   Next

Answer 1

You have nested the loops. This means that the inner loops are repeated at each loop of the outer loops. Eg If the three list boxes have 3, 4, and 6 elements the most inner loop will loop 3 x 4 x 6 = 72 times!

Instead make only one loop:

Dim n As Integer = _
    Math.Min(ListBox1.Items.Count, Math.Min(ListBox2.Items.Count, ListBox3.Items.Count))

For i As Integer = 0 To n - 1
    ListBox4.Items.Add( _
        ListBox1.Items(i).ToString + _
        ListBox2.Items(i).ToString + _
        ListBox3.Items(i).ToString)
Next