cis 115 lecture 3. forms form properties controls control properties event driven programming ...
TRANSCRIPT
CIS 115 Lecture 3
FormsForm propertiesControls Control propertiesEvent Driven ProgrammingForm EventsControl EventsEvent HandlersVB Example Program
A form is a container for controlsA form is used to design a GUI-based
window in a Windows applicationA form displays information and
receives input from the user. Always orient a form at a task as
defined by the user
Text – defines the text to display in the caption bar
StartPosition – determines position of form when it first appears (eg. CenterScreen)
Size.Width, Size.Height – the 2D area occupied by the form, in units of pixels
Location.X, Location.Y – the relative position of the form on the screen
Visible – can be seen by the user Enabled – the user can interact with the form
FormBorderStyle – determines the appearance and behavior of the borders of the form Sizable: (Default) Has min, max, and close buttons;
can be resized by dragging edges Fixed3D: Has a 3D look; min, max, and close
buttons; cannot be resized FixedSingle: Has single line border; min, max, and
close buttons; cannot be resized AcceptButton - designates which button on
the form is activated by the Enter Key Cancel Button - designates which button on
the form is activated by the ESC Key
Visual objects that are placed on a form to enable customized activities
Familiar Visual Basic controls: Label - displays text the user cannot change TextBox - allows the user to enter text Button – performs an action when clicked RadioButton - A round button that is selected or deselected with a
mouse CheckBox – A box that is checked or unchecked with a mouse click Form - A window that contains these controls
Built-in controls defined in Windows Form class library, and are defined with ToolBox and Form Designer or strictly with code
Text edit (TextBox—txt___) Text display (Label—default name or lbl___) Selection from a list (ListBox—lst___, ComboBox—
cbo___, ListView, TreeView, NumericUpDown…) Graphic display (PictureBox—pic___) Graphic storage (ImageList) Value setting (CheckBox—chk___, CheckListBox,
RadioButton,…) Date setting (DateTimePicker, MonthCalendar) Dialog boxes (OpenFileDialog, PrintDialog…) Menu controls (MainMenu, …) Commands (Button—btn___, LinkLabel…) Grouping other controls (GroupBox, TabControl,
Panel)
Common properties shared by many controls Name, Text Size.Height & Width, Location.X &Y, Dock BackColor: Sets the background (fill) color ForeColor: Sets the foreground (text) color CanFocus, ContainsFocus, Focused Visible & Enabled determine availability to user Font properties affect text display in the control
▪ Font, size, bold, etc. Tab Index & Tab Stop
Design Time Set in Properties Window
Run Time Set / Change in Code
Slide 2- 10
Specify the control name (btnExit)Then a dotThen the PropertyName (Visible)
controlName.propertyName btnExit.Visible
▪ refers to the Visible property of the btnExit control▪ The visible property values may only be true or false
Item to receive the value (Left Side)Assignment Indicator = Value to be assigned(Right Side)
VariableName = Value NumberVariable = 5
ControlName.PropertyName = Setting btnExit.Visible = False
▪ Assigns the value False to the Visible property of the btnExit control
▪ Causes the text of the btnExit control to become hidden to the user
txtFirstName.text = “Paul” txtLastName.text = “Overstreet”
Properties Text
▪ &Cancel -> Cancel▪ && -> &
Events Click
Use labels and link labels for text display Text property (no more Caption)
defines text to display User cannot change a label
LinkLabel enables hyperlinks Links.Add inserts a hyperlink into
text Must write event-handler to invoke
browser See example
Text box allows user to enter or edit data
Properties MaxLength, MultiLine AcceptsTab AcceptsReturn WordWrap ScrollBars
Events TextChanged
CheckState property Checked Unchecked Indeterminate
(checked but grayed)
Text property displays built-in caption
If chkMarried.CheckState = CheckState.Checked Then End If
ComboBox Properties Text DropDownStyle
▪ Simple▪ Dropdown▪ DropdownList
Sorted Methods
Items.Clear Items.Add Items.Remove
cboChoice.Items.Clear()cboChoice.Items.Add("First")cboChoice.Items.Add("Second")cboChoice.Items.Add("Third")cboChoice.Items.Add(TextBox1.Text)
cboChoice.Items.Remove("Third")
Executes code after a specified interval
Timer Event Unique event that executes
after the interval specified in the interval property expires
Interval Property 0 - 65,535 milliseconds
▪ 0 - means disabled▪ 60,000 milliseconds is one
minute Enabled property must
also be true for timer to work.
Timer control is never visible at run time
Stored in Component Tray at design time
Applications recognize and respond to events by executing code known as event procedures
Event: An action that is recognized by an object. User Actions
▪ Mouse Click▪ Entering Text▪ Pressing a Key
Program Calculations Triggered by the system
▪ Timer Event Handler: Code that is written by the
programmer to respond to an event Executes only when particular event occurs
Common Form Events Form1_Load() - Occurs before a form is
displayed for the first time. Form1_Activated() - Occurs when form
becomes the active window - through code or by user
Form1_Deactivate() - Occurs when the form loses focus and is not the active form
Form1_Closing() - Occurs when the form closes, either through an event or the windows close button being clicked
Many controls share a Common set of events to which they can react Click, DoubleClick MouseMove, MouseDown, MouseUp,
MouseWheel, MouseHover, MouseLeave KeyPress, KeyDown, KeyUp Resize DragDrop GotFocus LostFocus
Focus is when an object becomes the “Active Control”
Focus Event Sequence: Enter GotFocus Leave Validating Validated LostFocus
Create Event Procedure Double Click on Control Displays Code Window and Event Procedure
Stub for default eventOr
Open the Code Editor (F7 or View Menu:Code Command)
Select Control & Event from drop down windows in Code Editor
Event Code Goes In Here
Exit Button – Clicked Method (btnExit_Click)
Private Sub btnExit_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnExit.Click' End the applicationEnd
End Sub
Line Continuation Mark
Name of the event the procedure responds to
Name of the control that owns the event procedure
Marks the beginning of this event procedure
Ends the program
Event handled by this procedure
Input Controls
Process Events
Output Controls
UDIE – Implement the solution in VB:Create the Interface
Input Controls Output Controls
Set the Properties Configure the appearance and behavior of the
controlsWrite the Code to execute when events
occur Process the inputs to create the outputs
Using Visual Basic.Net create the following form
ObjectObject PropertyProperty SettingSetting
Form1Form1 TextText DemonstrationDemonstration
txtFirsttxtFirst TextText (blank)(blank)
txtSecondtxtSecond TextText (blank)(blank)
btnRedbtnRed TextText Change Color Change Color to Redto Red
When btnRed is clicked - Change txtFirst text color to red
Double Click on btnRedCode window should appear
(with Event Procedure Stub)
Add code to the event procedure stub: txtFirst.ForeColor = Color.Red
When the text is edited in txtFirst - Change txtFirst text color to blue
In Code WindowSelect the Control for the Event Procedure
txtFirst from the ClassName boxSelect the Event from the Method Name Box
TextChanged
Class Name Box
Method Name Box
Add code to the event procedure stub: txtFirst.ForeColor = Color.Blue
When txtFirst is deselected - Change txtFirst text color to black
In Code WindowSelect the Control for the Event Procedure
txtFirst from the ClassName boxSelect the Event from the Method Name Box
LeaveAdd code to the event procedure stub:
txtFirst.ForeColor = Color.Black
Click F5 or the Run ButtonType “Hello” into the 1st textbox
What HappensClick on the 2nd Textbox
What happened in txtFirst and Why Click on the Button
What happened in txtFirstType “Friends” into the 1st textboxStop Program by clicking Red X in
corner
Add a Button to your Form Name: btnExit Text Property: &Quit
Add a Button Click Event for this Button Code: END
Finds Syntax Errors (Errors in Programming Language)
Return to btnRed Click Event ProcedureAdd this line of Code:
txtSecond.text = Hello
Notice Wavy Blue Line – This indicates a Syntax Error that must be fixed.
Test All Events
Click Quit Button
Homework 1 Visual Basic Controls and Properties See handout for details and due date Questions?