CIS 338: VB.NET Components

Dr. Ralph D. Westfall April, 2011

Components = Building Blocks

form is the fundamental VB.NET component = interface between user and other code

parts of a form control box (click or double-click upper left

corner) Text (title) property title bar small buttons: minimize, maximize, close

follow along on laptops

Form Methods

if only one form, shows at Startup can stop it by clicking small Close (x) button

at top right, or run Close in code do NOT use [frmName].Hide with only one

form! [frmName.]Close closes form, and also shuts

down the project if there is only one form End shuts down the project if there is more

than one form

Controls

visible objects on forms or elsewhere built into Visual Basic.NET or available

from 3rd parties examples of built in form controls

Button, TextBox, Label, CheckBox, RadioButtons, ListBox, ComboBox, etc. (view names on Visual Studio.NET Toolbox buttons)

Commonly Used VB.NET Controls

Label – puts text on a form TextBox – accepts inputs, displays outputs (Command) Button – causes code to run CheckBox – accepts Yes/No inputs (Option) RadioButtons – selects only one

from multiple choices ListBox – select from a list of choices ComboBox – select from list or enter value

Sample Properties of Controls

properties = variables e.g., (Name) of form or control Location.X .Y = # of pixels from left

and top edges of “container” sets position on screen container = what item is inside a form is the container for Button,

etc. Size: Width Height are also in pixels Anchor – attaches to side(s) of the form

Sample Properties of Controls - 2

more properties Enabled – True means user can change

for a Text Box that shows a calculated output, set Enabled = False (or show output in a Label instead)

Visible = True (or False) guess what this does where use? why? 'code

Using Properties of Controls

can set during development (“design time”)can also use code to change (“run time”) example: disable a Go to Next Form

button until after user has entered inputs and clicked Enter button

use “dot notation” to reference properties txtPayment.Text = CStr(decPayment)

decPayment = CDec(txtPayment.Text) conversions needed with Option Strict On

Some Label Control Properties

can set in Properties window or in code AutoSize – label’s “box” expands to fit text Font – size (points), font (typeface), style

(bold, italic, etc.) ForeColor – text color BackColor – background color (behind text)

can use a white background color to make Label look like a TextBox (but why?)

Some TextBox Control Properties

setting content value (default) txtName.Text = "Bubba"

for handling larger quantities of text MultiLine – True enables text wrapping

goes to next line when reaches right side

ScrollBars determines if a scroll bar is used on a text box, and what type(s) (None | Horizontal | Vertical | Both)

(Command) Button Properties

can use & in Text property to set shortcut key [Alt] e runs &Exit, [Alt] r runs G&rin may see an underline if & is before a

letter in the middle of the word e.g., Grin

Enabled if =True button is usable, but not if

=False when would you set it =False?

CheckBox Properties

2 possible Checked (Boolean) Values: False (not checked) True (checked)

3 possible CheckState Properties: Unchecked Indeterminate (checked and grayed;

try it) Checked

(Option) RadioButtons

only one radio button at a time can be selected clicking one "unclicks" the other different than clicking 2+ checkboxes

can use a GroupBox (container) to set up separate groups of radio buttons user can only select one from each group

(Option) RadioButtons - 2

Checked property is either True or Falsetwo ways to run (checkboxes also) can use [name]_Click method to cause

code to run as soon as user clicks one can use If … Then … Else or a Select

Case structure to test a user choice later, instead of triggering an immediate action

GroupBoxes (are Containers)

can put other controls in a GroupBoxneed to 1st put GroupBox on form, then put controls into it GroupBox will not include controls already

on form, even if you put it over them

can change appearance Text – present or absent FlatStyle – Standard, Popup, or System ForeColor, BackColor, BackGroundImage

ListBoxes

2 different kinds of ListBox ListBox: selection is highlighted CheckedListBox: selection is checked

lst[name].SelectedIndex property item number of selected item in list (zero-

based, starts at 0, but is -1 if unselected)

lst[name].Items.Count property (2 dots) total number of items in ListBox 'code

Other List Box Properties

can use Sorted = True to sort, but this only sorts by left side of list if leftmost characters are the same

numbers are handled as text characters (lexical sort), so don't sort correctly e.g.,

119 1-9 (or a-9)5649 2-64 (or b-64, etc.)94 3-1199 4-5649 'prefix gives order

'or use leading zeros (0009, 0064 …)

ListBox Multiple Selection

0, 1, or many based on SelectionMode works on ListBox, not on CheckedListBox

0 None – disabled 1 One – can select only one item 2 MultiSimple – can select with mouse,

or arrow key followed by spacebar 3 MultiExtended – also use Shift, Ctrl

keys if no item is selected, then SelectedIndex

value is -1 regardless of SelectionMode

ListBox Multiple Selection - 2

total number of selected items = lst[name].SelectedItems.Count

VB.NET creates a collection of specific selected items can cycle through in a for loop e.g., For Each item inListBox1.SelectedItems MsgBox(item)Next

ListBox Properties that Are Useable in Code

.SelectedItem property shows user's 1st selected item (simple approach)str[variable] = lst[name].SelectedItem

.SelectedIndex property shows the sequential identifier of selected item collection of items in the ListBox (1st) selected item # is lst[name].ListIndex

lst[name].Items(lst[name].ListIndex)

Programmable List Box Properties - 2

can set default selection in code with SelectedIndex property 1st item in ListBox has SelectedIndex

of 0 2nd item has 1 SelectedIndex of -1 means that none

is selectedlst[name].SelectedIndex = 2 'which item?

can't set this in Properties window

ListBox & Collection Together

lst[name].Items(lst[name]._SelectedIndex)orlst[name].Items.SelectedItem

als[name](lst[name]._ SelectedIndex)

Joelst[name].Items(Items(lst[name].SelectedIndex)

123456789als[name](Items(lst[name].SelectedIndex)

Analst[name].Items(1) ' hard coded

345678901als[name](1) ' hard coded

Adding Items to ListBox

using Items editor via Properties window type in items, then click OK can also paste into the editor window

programmaticallylst[name].Items.Add("CIS")lst[name].Items.Add(str[variable]) can load values into a parallel ArrayList

(unlike an array, don't need to use a counter)als[name].Add(191919) 'code

ComboBox

like a combination (combo) of a TextBox and a ListBox user can type information into the

TextBox part to either enter an item not in the list or scroll down to item(s) in the (Sorted = True) list that start with the same letters

properties and methods are usually same or similar to those of a ListBox

ComboBox Properties

DropDownStyle property 0 Simple (TextBox on top of a ListBox)

can select an item or type in something not in the ListBox part (Prof. Westfall's FAVORITE!!)

1 Dropdown (ListBox drops down on a click) can type in an item or initial letter(s), but don't see

any match from the ListBox until it drops down 2 DropdownList (ListBox drops down on click)

can't type anything in the TextBox part, but must click to drop down the ListBox to select an item

ComboBox Properties - 2

Text property (for Styles Simple or DropDown) can set it as a default selection, or

make it be an instruction to the user when it runs, or leave it blank

code can access .Text property to get user inputs that are not in the list(box)

ComboBox Properties - 3

can add objects to a ComboBox and make one attribute the DisplayItemcan then access other attributes of selected item e.g., select name, get Social Security #

'code

Controlling Tab Sequence

if a control's TabStop property = True, user can use tab key to move from one control to the next sequence is initially determined by

order that item was added to form set TabStop = False for items that will

not be used for input (e.g. a Label or a TextBox or ListBox that displays outputs)

Changing Tab Sequence

can change by changing TabIndex use a large number to make an item last VB 6 changed tab indices to compensate

for other changes Visual Basic.NET seems to keep track of

this in another way tutorial (click Types of Windows>Tab

Order)

set TabStop=True for Radio Buttons

Clicking to Change Tab Stops

in VB.NET, can mouse click items to change their tab sequence View>Tab Order then click each item in the order that

you want for the tab sequence repeated clicks on same item cycles

through the TabIndex values then click View>Tab Order (toggle it

off) to set new values

Clicking to Change Tab Stops - 2

note that Labels have a TabIndex property too, but not a TabStop property so can't tab to them could click them repeatedly to set all the

values to 0, but not necessary

note that tab values in View>Tab Order don't match with TabIndex properties

Clearing Common Controls

sometimes need to clear (remove contents) of a control txtName.Text = Nothing or txtName

= "" chkComputerOwner.Checked = False rdoCategory.Checked = False lstPersons.ClearSelected() cboCities.SelectedItem = Nothing

Design Tips for Controls

hold down left mouse button and use cursor to select multiple controls or hold Ctrl key and click items

after multiple items are selected, can move them as a groupcan change properties of all selected controls by changing in one control e.g., Font on Labels, Format>Align

Visual Studio's Format Menu

horizontal or vertical spacing increase/decrease, make equal,

remove

make same size size to grid (all corners on grid points)

alignment tops, lefts, etc.

Showing Grid Lines on Form

it can be helpful in designing a form to have grid lines showing during designTools>Options>Windows Forms Designer>General>Layout Settings>click Show Grid option SnapToGrid LayoutMode forces controls

to space themselves based on grid

Exercise

put a Button on a Form, and several other input controls covered todayclick the Button, write code to put the keyboard inputs from one control into a different kind of control that takes Texttest, and then repeat with another pair of controls