listbox,combobox,Visual basic 6.0

5/12/2018 listbox,combobox,Visual basic 6.0 - slidepdf.com

http://slidepdf.com/reader/full/listboxcomboboxvisual-basic-60 1/27

VISUAL BASIC CONTROLSLIST BOXES & COMBO BOXES



LIST BOX & COMBO BOX

Combo box tool List box tool



(CONTD«.)



A DDING ITEMS TO A LIST

We can add items to a list box at either design time or at runtime.

A t design time, we can use the List property, which is a veryhandy array of the items in the list box; and at runtime, we canuse both the List property and the AddItem() method.

Here·s how we use the List property in code,

ListBox .List(index ) [= string ]

We can track the total number of items in a list box usingListCount property

We·ll use ListCount as the maximum value to loop to.

A t runtime, we can either use the indexed List property asdetailed previously, or the

AddItem() method this way:Private Sub Form_Load()

List1. A ddItem (´Item 1µ)




End Sub



REFERRING TO ITEMS IN A LIST BY INDEX

When we add items to a list box, each item is given an

index, and we can refer to the item in the list box usingthis index (for example, you can get the item·s text by

using the List property: List(index)).

The first item added to a list box gets the index 0,

the next index 1, and so on. When the user selects an item in a list box, you can get

the selected item·s index with the list box·s ListIndex

property.

For example,Private Sub Form_Load()

List1. A ddItem ("Item 0")




End Sub



RESPONDING TO LIST BOX EVENTS

C lick And DblC lick

y We use two main events with list boxes: Click and DblClick.y How we actually use them is up to you, because different

programs have different needs.

y We use the Click event just as we use the Click event in

a button, with a Click event handler.

y Here, we display the item in the list box the user has clicked,

using the ListIndex property (we can get the selecteditem·s text with List1.List(ListIndex) or with List1.Text):

Private Sub List1_Click()

MsgBox " You clicked item " & Str(List1.ListIndex)

End Sub

y A nd displaying the selected item is the same for DblClick³you just add a DblClick handler with the code we want:

Private Sub List1_DblClick()

MsgBox " You clicked item " & Str(List1.ListIndex)

End Sub



(CONTD«.)

Multiselect List Boxes

y List boxes can also be multiselect list boxes, which

means the user can select a number of items in the

list box.

y If our list box is a multiselect box, you can determine

which items the user has selected by using theSelected property this way:

For intLoopIndex = 0 To List1.ListCount - 1

If List1.Selected(intLoopIndex) Then

...

End If

Next intLoopIndex



REMOVING ITEMS FROM A LIST

We can remove items from a list box at designtime simply by deleting them in the List

property.

A t runtime, you use the RemoveItem()

method.

Here·s an example; in this case, we add four

items, Items 0 through 3 to a list box:Private Sub Form_Load()





End Sub

Private Sub Command1_Click()

List1.RemoveItem 1

End Sub



SORTING A LIST BOX

We can alphabetize the items in a list box bysetting its Sorted property to True (it·s False

by default) at design time or runtime.



DETERMINIG HOW M A NY ITEMS A RE IN A

LIST BOX

We can use the ListCount property to

determine how many items are in a list box.

When setting up loops over the items in a list

box, we should note that ListCount is the totalnumber of items in a list, whereas index values

start at 0, not 1.

For example,Private Sub Command1_Click()

Dim intLoopIndex A s Integer


...

Next intLoopIndex

End Sub



DETERMINING IF A LISTBOX ITEM IS SELECTED

We get the index of the selected item in a list box with the

ListIndex property. If no item is selected, ListIndex will be ²1.

We can get the text of a list·s selected item as List1.Text or

List1.List(List1.ListIndex).

We can use a list box·s Selected array to determine if individual items in the list box are selected or not.

A nd we check the Selected array for each item to find

the selected item:Private Sub Command1_Click ()

Dim intLoopIndex


If List1.Selected(intLoopIndex) Then

MsgBox " You selected " & List1.List(intLoopIndex)

End If

Next intLoopIndex

End Sub



USING MULTISELECT LIST BOXES

A multiselect list box allows the user to select a

number of items at one time.

We make a list box into a multiselect list box with the

MultiSelect property.

The user can then select multiple items using the

Shift and Ctrl keys. Here are the possible settings for MultiSelect:

0³ Multiple selection isn·t allowed (this is the default).

1³Simple multiple selection. A mouse click or pressing the

spacebar selects or deselects an item in the list. (Arrow keys

move the focus.)

2³Extended multiple selection. Pressing the Shift key and

clicking the mouse or pressing the Shift key and one of the

arrow keys extends the selection from the previously selected

item to the current item. Pressing the C trl key andclicking

the mouse selects or deselects an item in the list.



M AK ING LIST BOXES SCROLL

HORIZONT A LLY

If we break up the list into columns using the

C olumns property.

W hen that property is set to 0, the default, the

list box presents just a vertical list to the user. When you set the Columns property to

another value, the list box displays its items

in that number of columns instead.



USING CHECK M A RK S IN A LIST BOX

When you use checkmark list boxes, selected

items appear with a checkmark in front

of them. You can make a list box into a

checkmark list box with its Style property, which can take these values:

0³Standard list box (the default)

1³C heckmark list box



CRE A TING A LIST BOX

We can use the Clear method to clear a list box. We just use clear like this: List.C lear.

Here·s how that looks in code; in this case, we·re

clearing a list box, List1, when the user clicks a

command button: Private Sub Command1_Click()

y List1.Clear

End Sub



CRE A TING SIMPLE COMBO BOXES,

DROP-DOWN COMBO BOXES & DROP-

DOWN LIST COMBO BOXES

Combo boxes are those controls that usually display

a text box and a drop-down list.

In fact, we might think there is only one kind of

combo box, but there are really three types, and weselect which type we want with the combo box·s

Style property.

The default type of combo box is probably what we

think of when we think of combo boxes, because, as

mentioned, it is made up of a text box and a drop-

down list.

However, we can also have combo boxes where the

list doesn·t drop down.



(CONTD«)

Here are the settings for the combo box Style

property: VbComboDropDown³0; drop-down combo box. Includes a

drop-down list and a text box. The user can select from the list or

type in the text box. (This the default.)

VbComboSimple³1; simple combo box. Includes a text box

and a list, which doesn·t drop down. The user can select from thelist or type in the text box. The size of a simple combo box includes

both the edit and list portions. By default, a simple combo box is

sized so that none of the list is displayed. Increase the Height

property to display more of the list.

VbComboDrop-DownList³2; drop-down list. This style

allows a selection only from the drop-down list. This is a good oneto keep in mind when you want to restrict the user·s input;

however, if you want to use this one, you should also consider

simple list boxes. The selected item appears in the (read-only) text

box.



A DDING ITEMS TO A COMBO BOX

A combo box is a combination of a text box and a list box, so at

design time, we can change the text in the text box part by

changing the Text property.

We change the items in the list box part with the List

property.

A t runtime, we can add items to a combo box using the

AddItem() method, which adds items to the list box part.

We can also add items to the list box using the List property,

which is an indexed array of items in the list box.

If we want to set text in the text box, set the combo box·s Text

property.

Here·s an example,Private Sub Form_Load()

Combo1. A ddItem ("Item 0")




End sub



RESPONDING TO COMBO BOX SELECTIONS

Combo boxes are combinations of text boxes and

list boxes, and that combination means that

there are two sets of input events: Change

events when the user types into the text box

and Click or DblClick when the user uses

the mouse.

Note that, unlike standard list boxes, you

cannot make multiple selections in a combo box·s

list box.



(CONTD«.)

C hange Events

y When the user changes the text in a combo box, a

Change event occurs, just as it does when the

user types in a standard text box.

y We can read the new text in the text box with the

Text property

Private Sub Form_Load()



Combo1. A ddItem ("Item 2")Combo1. A ddItem ("Item 3")

End Sub

Private Sub Combo1_Change()

MsgBox "New text is: " & Combo1.Text

End Sub



(CONTD«)

C lick Eventsy We can also get Click events when the user

makes a selection in the list box using the

mouse.

y We can determine which item the user clicked using

the combo·s ListIndex property (which holds theindex of the clicked item) or get that item·s text using

the Text property, because when we click an item, it

is made the new selected item in the text box.



(CONTD«.)

DblC lick Events

y We might expect that where there are Click events

there are DblClick events, and that·s true³but

for simple combo boxes only (Style =

VbComboSimple, where VbComboSimple is a Visual Basic constant that equals 1).

y When you click an item in the list part of a combo

box once, the list closes, so it·s impossible to double-

click an item³except in simple combo boxes, where

the list stays open at all times



REMOVING ITEMS FROM A COMBO BOX

Just as with list boxes, you can remove items

from combo boxes using the RemoveItem()

method.

We just pass the index of the item you want to

remove from the combo box·s list to RemovPrivate Sub Command1_Click()

Combo1.RemoveItem 1

End SubeItem().



GETTING THE CURRENT SELECTION IN A

COMBO BOX

When we make a selection in a combo box, that

new selection appears in the combo box·s text

box, so it·s easy to get the current selection³we

just use the combo box·s Text property.

We can also get the currently selected item·s

index in the combo box·s list using the ListIndex

property. If no selection is made (for

instance, when the form first loads and the

combo·s text box is empty), this property willreturn ²1.



SORTING A COMBO BOX

We can leave the work up to the combo box itself if you set its Sorted property to True

Default is false in the sorted property



CLEARING A COMBO BOX

the current items there one by one withRemoveItem()

No, we can clear a whole combo box at once with the

Clear() method.Private Sub Command1_Click()

Combo1.Clear

End Sub



LOCKING A COMBO BOX

You can lock a combo box by setting its Locked

property to T r ue.

W hen locked, the user cannot enter text in the

combo·s text box and cannot make selections fromthecombo·s list (although if the list is drop-down,

it will still open).

However, when programmers think of ´lockingµ a

combo box, it·s not usually the Locked property

thatthey want.

listbox,combobox,Visual basic 6.0

Documents

Transcript of listbox,combobox,Visual basic 6.0