vb011 list boxes vb15. vb012 list boxes a list box contains a list of items one underneath the other...

VB01 1

List Boxes

VB15

VB01 2

List Boxes

• A list box contains a list of items one underneath the other

DanPeterJaneRobertElaineNiamhAlan

VB01 3

lstName.AddItem

lstNaughty.AddItem “Peter”

Adds Peter to the list called lstNaughty

Peter

VB01 4

lstName.AddItem

lstNaughty.AddItem “Mike”

Adds Mike to the list called lstNaughty

PeterMike

VB01 5

lstName.Clear

lstNaughty.Clear

Removes all the items from the list box

VB01 6

lstName.List (int)

RodJaneFreedyZippyBungleJeferyArcher

Individual list box items can be referenced by a subscript just like an array

lstNaughty.List (0) is “Rod”

lstNaughty.List (3) is “Zippy”

lstNaughty.List (4) is “Bungle”

VB01 7

lstName.List (int)

RodJaneFreedyZippyBungleJeferyArcher

The .list method can also be used to change an item.

lstNaughty.List (3) = “Peter”

RodJaneFreedyPeterBungleJeferyArcher

VB01 8

lstName.ListCount

• The .ListCount method is used to determine the number of items in the list

• lntNaughty.ListCount is 7

RodJaneFreedyPeterBungleJeferyArcher

VB01 9

lstName.RemoveItem (int)

• The .RemoveItem method is used to remove a particular item

• lntNaughty.RemoveItem (4)

RodJaneFreedyPeterBungleJeferyArcher

RodJaneFreedyPeterJeferyArcher

VB01 10

Using List Boxes- Example 1

RodJaneFreedyZippy

PatRory

Add name

Naughty

Nice

Naughty NiceSanta’s List

VB01 11

Santa’s List

RodJaneFreedyZippy

PatRory

Add name

Naughty

Nice

Naughty Nice

lstNaughty lstNice

optNaughty

txtName

VB01 12

Santa’s List - Code

strName = txtName.Text

If optNaughty.value then

lstNaughty.AddItem strName

Else

lstNice.AddItem strName

End If

VB01 13

Using List Boxes- Example 2

• lstNaughty is a list of names• Write a VB program that

counts the number names in the list that begin with the letter R and puts this number into a variable called intTotalCount

RodJaneRyuichiRoryBungleJeferyArcher

VB01 14

Algorithm

Set intTotalCount = 0

For each name

If it begins with “R” then

Add one to intTotalCount

Next name

VB01 15

Dim intTotalCount As IntegerDim strName as StringintTotalCount = 0For n = 0 to lstNaughty.ListCount - 1

strName = lstNaughty.List (n)If left (strName, 1) = “R” Then

intTotalCount = intTotalCount + 1End If

Next n

VB01 16

Dim intTotalCount As IntegerDim strName as StringintTotalCount = 0For n = 0 to lstNaughty.ListCount - 1

strName = lstNaughty.List (n)If left (strName, 1) = “R” Then

intTotalCount = intTotalCount + 1End If

Next n

VB01 17

Dim intTotalCount As IntegerDim strName as StringintTotalCount = 0For n = 0 to lstNaughty.ListCount - 1

strName = lstNaughty.List (n)If left (strName, 1) = “R” Then

intTotalCount = intTotalCount + 1End If

Next n

VB01 18

Dim intTotalCount As IntegerDim strName as StringintTotalCount = 0For n = 0 to lstNaughty.ListCount - 1

strName = lstNaughty.List (n)If left (strName, 1) = “R” OR left (strName, 1) = “r” Then

intTotalCount = intTotalCount + 1End If

Next n

VB01 19

Using List Boxes - Example 3

RodJaneRyuichiRoryBungleJeferyArcher

9874596

Two list boxes lstNames and lstAges are used to store the names and ages of children respectively.

The nth item in lstAges is the age of the child whose name in the nth item in lstNames

Write a program that finds the name of the youngest child and stores it in strYoungest

VB01 20

Algorithm• Set strYoungest to the first name in lstNames• Set the intYoungestSoFar to the first age in

lstAges• Go though the ages one by one• For each item in intAges• If it is smaller than intYoungestSoFar then

– Set intYoungerstSoFar to it– Set strYoungest to the corresponding name

• Go on to the next one

VB01 21

Dim strYoungest As StringDim intYoungestSoFar As IntegerstrYoungest = lstNames.List(0)intYoungestSoFar = lstAges.List(0)For n = 0 to lstAges.ListCount - 1

If lstAges.List(n) < intYoungestSoFar ThenintYoungestSoFar = lstAges.List(n)strYoungest = lstNames.List(n)

End IfNext n

VB01 22

Dim strYoungest As StringDim intYoungestSoFar As IntegerstrYoungest = lstNames.List(0)intYoungestSoFar = lstAges.List(0)For n = 0 to lstAges.ListCount - 1

If lstAges.List(n) < intYoungestSoFar ThenintYoungestSoFar = lstAges.List(n)strYoungest = lstNames.List(n)

End IfNext n

VB01 23

Dim strYoungest As StringDim intYoungestSoFar As IntegerstrYoungest = lstNames.List(0)intYoungestSoFar = lstAges.List(0)For n = 0 to lstAges.ListCount - 1

If lstAges.List(n) < intYoungestSoFar ThenintYoungestSoFar = lstAges.List(n)strYoungest = lstNames.List(n)

End IfNext n

VB01 24

Dim strYoungest As StringDim intYoungestSoFar As IntegerstrYoungest = lstNames.List(0)intYoungestSoFar = lstAges.List(0)For n = 0 to lstAges.ListCount - 1

If lstAges.List(n) < intYoungestSoFar ThenintYoungestSoFar = lstAges.List(n)strYoungest = lstNames.List(n)

End IfNext n

VB01 25

Dim strYoungest As StringDim intYoungestSoFar As IntegerstrYoungest = lstNames.List(0)intYoungestSoFar = lstAges.List(0)For n = 1 to lstAges.ListCount - 1

If lstAges.List(n) < intYoungestSoFar ThenintYoungestSoFar = lstAges.List(n)strYoungest = lstNames.List(n)

End IfNext n

VB01 26

Using List Boxes - Example 3

RodJaneRyuichiRoryBungleJeferyArcher

910

71415

96

Two list boxes lstNames and lstAges are used to store the names and ages of children respectively.

The nth iten in lstAges is the age of the child whose name in the nth item in lstNames

Write a program that removes all of the children who are 10 years of age or older

VB01 27

RodJaneRyuichiRoryBungleJeferyArcher

910

71415

96

RodRyuichiJeferyArcher

9796

VB01 28

Algorithm

For each child

If age >= 10 then

Delete that childs name from the list

End If

Next child

VB01 29

For n = 0 to lstAges.ListCount - 1

If lstAges.List (n) >= 10 Then

lstNames.RemoveItem (n)

End If

Next n

VB01 30

RodJaneRyuichiRoryBungleJeferyArcher

910

71415

96

RodRyuichiRoryJefery

910

71415

96

What happened!!???

VB01 31

RodJaneRyuichiRoryBungleJeferyArcher

910

71415

96

RodRyuichiRoryJefery

910

71415

96

What happened!!???

The ages weren’t removed

Wrong names removed

VB01 32

For n = 0 to lstAges.ListCount - 1

If lstAges.List (n) >= 10 Then

lstNames.RemoveItem (n)

lstAges.RemoveItem (n)

End If

Next n This will remove ages

VB01 33

For n = 0 to lstAges.ListCount - 1

If lstAges.List (n) >= 10 Then

lstNames.RemoveItem (n)

lstAges.RemoveItem (n)

As items are deleted the size of the list box changes.

Does n count to whatever ListCount-1 was at the start or does it check ListCount every time? ?

VB01 34

n = 0

Do Until n > lstAge.ListCount

If lstAges.List (n) >= 10 then

lstAges.RemoveItem (n)

lstNames.RemoveItem (n)

Else

n = n + 1

End If

Loop