ISM 3253 Topics 2: Form, Control, Event

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ISM 3253 Topics 2 Form, Control, Event

• Program Elements
• Assignment Operations
• Events Event Procedures
• Properties
• Tab Order and Access Keys

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Review Visual Studio Programming

• A computer program consists of instructions
  readable by the computer which direct its
  operations
• In modern development, programs begin as
  instructions readable by (trained) humans
• And end up as instructions readable by the
  computer (and generally incomprehensible to all
  but the most sophisticated developers)

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Review Visual Studio Programming (cont.)

• Most programs consist of many parts
• Visual Studio and Visual Basic support
• Authoring the component parts of the programs
• Managing the program parts
• Converting the parts you write into machine
  readable format
• Combining the parts you write with a huge
  collection of pre-written instructions
• Many other tasks

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Projects

• Projects may consist of many parts
• Solutionmultiple programsdeveloped together
• We will not use this
• Projectone program
• All elementsare optional
• but it musthave at least one

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ProjectsForms

• Forms provide the visual interface for a
  program
• Forms contain
• Controls
• Properties
• Methods
• Events with code
• Non-event code
• Controls also contain Properties, Methods, and
  Event Code

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Assignment Operations (Our First Code)

• A common code involves assigning a value to a
  container
• Both Container and Value can be
• Property
• Variable
• Object
• In this use the equal sign is the assignment
  operator

Container Value
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Assignment Operations (cont.)

• Examples
• intQuantity 123places the value 123 into the
  variable intQuantity
• stLastName Jonesplaces the value Jones
  into the variable stLastName
• lblLastName.Text stLastNameplaces the contents
  of the variable stLastName (whatever they are)
  into the Text property of the label control
  lblLastName

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Events

• Forms, Controls, and Classes recognize events
• Events are predefined (or programmer defined)
  actions against an object
• If the action occurs
• And if there is code written for the event
• Then the code will execute
• Three kinds of events for forms and controls
• Commonly used
• Less commonly used
• Almost never used

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Events (cont.)

• Our first eventThe Click Event for a button

cmdTransfer
txtTransfer
lblTransfer
Private Sub cmdTransfer_Click(ByVal sender As
System.Object, _ ByVal e As System.EventArgs)
Handles cmdTransfer.Click '

' Places the contents of the txtTransfer text
box ' into the lblTransfer label text
property '
lblTransfer.Text
txtTransfer.Text End Sub
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Events (cont.)
Line continuation character
Name of the event procedure
Event Arguments
Private Sub cmdTransfer_Click(ByVal sender As
System.Object, _ ByVal e As
System.EventArgs) Handles cmdTransfer.Click
Control and event that triggers the code

• Event Arguments are created automatically and are
  only used for advanced purposes
• The procedure name and Handles expression are
  also created automatically
• The event procedure header (what we are seeing
  here) is actually created as one long line
• Use the line continuation character to break it
  into two physical lines
• But still treated as one logical line

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Creating Event ProceduresDefault Events

• Double-clicking a control or form in design view
  creates the template for the default event
• Form Load event
• Button Click event
• Text Box TextChanged event
• Label Click event
• Check Box Radio Button CheckChanged event
• Combo Box List Box SelectedIndexChanged
• Date Time Picker ValueChanged event
• NumericUpDown ValueChanged event

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Creating Event ProceduresOther Events

• The at the top left corner of the code window is
  a drop-down list of all objects on the form
• Select the object whose event you want to program

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Creating Event ProceduresOther Events

• The right side of the code window contains a list
  of all events supported by form/control selected
  in the left box
• Selecting an event will create the event code
  template for that control and event combination

Selected Object (left side)
Supported Events (right side)
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Creating Event ProceduresOther Events

• There can be a dizzying variety of events
  supported for most objects
• Most are for events so obscure that you would
  never use them
• Some are incredibly useful and you should learn
  these over time

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Event ProceduresMultiple Events

• You will often want the same code to run for
  multiple events and/or controls
• Add the control/event combination to the Handles
  expression

Private Sub txtTransfer_GotFocus Handles
txtTransfer.GotFocus, _ txtTransfer.Click,
txtTest.GotFocus, txtTest.Click ltEvent
Codegt End Sub
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Event ProceduresMultiple Events (cont.)
Private Sub txtTransfer_GotFocus(ByVal sender As
Object, _ ByVal e As System.EventArgs) Handles
txtTransfer.GotFocus, _ txtTransfer.Click,
txtTest.GotFocus, txtTest.Click
'
' Handles the GotFocus and
Click events of all text boxes on ' the
form. ' Automatically selects the contents
of the text box so that ' text can be
replaced by typing '
'
Create a text box object Dim theTextBox As
TextBox ' Set the object to the control that
triggered the event theTextBox sender
' Select the text in the text box
theTextBox.SelectionStart 0
theTextBox.SelectionLength theTextBox.Text.Lengt
h End Sub
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Properties

• Visual design elements (forms and controls) have
  properties that
• Control their behavior
• Determine their appearance
• Interact with the user
• Properties may be set at
• Design time
• Run time
• In code
• With user interaction
• Both Design Run Time

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Design Time Properties

• Selecting an object in formdesign mode gives
  access to the objects properties in
  theproperties window
• These properties will be thedefault properties
  when a formis first created
• Changes implemented in code or by user
  interaction will persistas long as the form is
  open oruntil they are changed again

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Name Property

• Every object has a Name property that controls
  how your object is addressed in code
• If the object is addressed in code you must
  rename your object to indicate its
• Type (use a prefix)
• Purpose of use (rest of the name)
• You need not rename labels that are not addressed
  on code

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Name Property (cont.)

• Examples
• lblLastName label
• btnCancel button
• txtStreetAddress text box
• dtpBirthDate date time picker
• cboStyle combo box
• lstDepartment list box
• chkActive check box
• rdoMaritalStatus radio button
• CustomerForm form

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Important Form Properties

• Accept Buttonbutton whose code will execute if
  the Enter key is pressed
• Cancel Buttonbutton whose code will execute if
  the Escape key is pressed
• Textdisplays in the title bar
• ControlBox, FormBorderStyle, Maximize
  Minimize Buttons
• StartPositionwhere form will initially load
• SizeWidth Height of the form

Removing these will give a form with no title
bar
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Common Control Properties

• Textwhat is displayed in the control
• Left / Topcoordinates in pixels from the upper
  left corner of the form for the location of the
  upper left corner of the control
• Width / Heightsize in pixels of the control
• EnabledControl is always visible but can be
  toggled to active or inactive dimmed
• VisibleControl is visible or not
• TabIndexsequence of the control in the forms
  tab order

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Key Interaction Control Value Properties

• Text BoxText
• Check BoxChecked
• Radio ButtonChecked
• Combo Box List BoxText, SelectedIndex,
  SelectedValue, SelectedText
• Date Time PickerValue

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Reading Setting Properties in Code

• Properties may be read and set in code by
  referring to them on the appropriate side of an
  assignment operator (equal sign)

Private Sub cmdTransfer_Click(ByVal sender As
System.Object, _ ByVal e As System.EventArgs)
Handles cmdTransfer.Click '

' Places the contents of the txtTransfer text
box ' into the lblTransfer label text
property '
lblTransfer.Text
txtTransfer.Text End Sub
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Properties in Code
Private Sub btnCatchMe_MouseMove(ByVal sender As
Object, _ ByVal e As System.EventArgs)
Handles btnCatchMe.MouseMove
'
' What is going on here????
'
If Now.Second lt 55 Then
If Now.Second lt 30 Then
btnCatchMe.Top 20 Else
btnCatchMe.Top Me.Height - btnCatchMe.Height -
30 End If If Now.Second Mod 2 1
Then btnCatchMe.Left 20 Else
btnCatchMe.Left Me.Width - btnCatchMe.Width
- 20 End If End If End Sub
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Getting Stupid with Properties

• You can do VERY stupid with appearance properties
• BackColor
• ForeColor
• Font
• Experiment and get it out of your system
• Then stick with the defaults for your work in
  this class

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Setting Tab Order

• After the form is complete there is an easy to
  set the whole forms tab order sequence
• Select View Tab Order from the menu
• Click box by each control in the tab order you
  want
• If you screw it up start over
• Set individual control Tab Stop properties to
  False to exclude from the tab order

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Setting Access Keys

• Putting an in the Text property of a control
  makes the following letter the hot key for the
  control.
• Gives control focus if Alt-Letter is pressed
• Executes button if it is a buttons Access key
• Text boxes have no permanent Text property
• Set the hot key in a label that immediately
  precedes the text box in the forms tab order
• Labels cannot get focus but focus will shift to
  the text box