CSCI 3131.01 Chapter 2 Creating Application with Visual Basic Instructor: Bindra Shrestha
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Transcript of CSCI 3131.01 Chapter 2 Creating Application with Visual Basic Instructor: Bindra Shrestha
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CSCI 3131.01
Chapter 2 Creating Application with Visual Basic
Instructor: Bindra Shrestha
University of Houston – Clear Lake
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Acknowledgement
Dr. Xinhua Chen
And
Starting Out with Visual Basic 2010 by Tony Gaddis and Kip Irvine
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Topics•Building the Directions application•Responding to events•Modifying properties of a control with code: Text, Autosize, BorderStyle, and TextAlign properties•Clickable images•Using Visual Studio Help•Debugging an application
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Steps to Create an Application
1.Clearly define what the application is to do.2.Visualize the application running on the computer and design its user interface3.Make a list of the controls needed.4.Define the values of each control’s relevant properties.5.Start Visual Basic and create the forms and other controls
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Clearly Define the Task of the Application
Purpose: Display a map to the Highlander HotelInput: NoneProcess: Display a formOutput: Display on the form a graphic image showing a map
Specifications of the Application
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Visualize and Design the User Interface
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Points to Watch while Designing User Interface
Follow the convention of Windows Graphic User Interface (GUI) design.
Most Windows application consists of (1) a main (primary) window, (2) possibly some other primary windows, and (3) one or more secondary windows, called dialog boxes.
The Windows Notepad application uses the primary window for editing the document; it uses a dialog box for selecting the font related properties.
Primary windows can be resized, minimized, maximized and closed by the user.
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Using Graphics, Fonts and Color in User Interface
Using graphics, fonts and colors appropriately helps the information flow more efficiently from the user interface to the users.
Inappropriate use of graphics, fonts and colors distracts the users and may also offend some of the users.
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List the Controls Needed
Control Type Control Name Description
Form Form1 A small form that will serve as (Default Name) the window onto which the other
controls will be placed
Label Label1 Displays the message(Default Name) "Directions to the Highlander
Hotel"
PictureBox PictureBox1 Displays the graphic image(Default Name) showing the map to the hotel
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Define Control Relevant Property Values
• Form– Name: Form1– Text: "Directions"
• Label– Name: Label1– Text: "Directions to the Highlander Hotel"– TextAlign: MiddleCenter– Font: Microsoft sans serif, bold, 18 point
• PictureBox– Name: PictureBox1– Picture: HotelMap.jpg– SizeMode: StretchImage
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Use VB to Create the Application
• Establish the Form and set its Text property• Add a Label control
– Position and resize it on the form– Set Text, TextAlign, and Font properties
• Add a PictureBox control– Position and resize it on the form– Set Image property to display HotelMap.jpg
• Run the application• Close and save the application
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Responding to Events
An Application Responds to Events, Such As •Mouse Clicks•Keyboard Input
The code that handles the events are called Event Handlers or Event Procedures
Write the Event Procedures for the Directions Application
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Augment the Hotel Application
• Now the hotelowner wants toadd an optionto view writtendirections:
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Controls to be Added
Control Type Control Name Description
Label lblDirections Displays written directions to the hotel
Button btnDisplayDirections When clicked, causes lblDisplayDirections text to appear on the form
Button btnExit Stops the applicationwhen clicked
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Control Properties
• Label:
– Name: lblDirections– Text: “Traveling on I-89, take…”– Visible: False
• Button:
– Name: btnDisplayDirections– Text: “Display Directions”
• Button:
– Name: btnExit– Text: "Exit"
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Method btnDisplayDirections_Click
Private Sub btnDisplayDirections_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnDisplayDirections.Click' Make the directions visiblelblDirections.Visible = True
End Sub
Line Continuation MarkName of the event the procedure responds to
Name of the control that owns the event procedure
Marks the beginning of this event procedure
Makes the control lblDirections visible:Assigns the value True to the Visible Propertyof the lblDirections control.
Event handled by this procedure
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Syntax for Referring to the Value of a Control's Property• Specify the control name (lblDirections)
• Then a dot• Then the PropertyName (Visible)
• For example:– lblDirections.Visible– refers to the Visible property of the lblDirections
control– The visible property values may only be true or
false
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Syntax for an Assignment Statement
• Specify the item to receive the value • Then the equal symbol• Then the value to be assigned • For example:
– lblDirections.Visible = True– Assigns the value True to the Visible property of
the lblDirections control– Causes the text of the lblDirections control to
become visible to the user
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Method btnExit_Click
Private Sub btnExit_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnExit.Click' End the application by closing the windowMe.Close()
End Sub
Line Continuation MarkName of the event the procedure responds to
Name of the control that owns the event procedure
Marks the beginning of this event procedure
Closes the current form, referred to as Me, and ends the program
Event handled by this procedure
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Modifying the Text Property in Code
Private Sub btnFeet_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnFeet.Click
' Display the conversion to feet.lblMessage.Text = "1 Kilometer = 3,281 feet"
End Sub
Assigns the string to the right of the equal sign to the text property of lblMessageThis replaces the previous text propertyof lblMessage with the new value shown
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AutoSize Property for Labels
• AutoSize is a Boolean (either True or False) Property of labels
• False (the default) means the box size will not change, regardless of the amount of text assigned to it
• True means the box will automatically resize itself to fit the amount of text assigned to it
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BorderStyle Property for Labels
• BorderStyle determines the look of the box– None (the default) means no border– FixedSingle results in a border one pixel wide– Fixed3D gives the border a recessed 3-dimensional
look
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TextAlign Property for Labels
• The value of TextAlign establishes the alignment (or justification) or the text: TopLeft TopCenter TopRight
• The assignment statement below forces the text of lblTitle to appear in the middle center of the label
lblTitle.TextAlign = ContentAlignment.MiddleCenter
MiddleLeft MiddleCenter MiddleRight
BottomLeft BottomCenter BottomRight
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Clickable Images
Controls other than Buttons can have Click event procedures.
PictureBox controls can respond to mouse clicks
For example, if a national flag image is clicked, you may use a label to display the name of the country:
Private Sub picUSA_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles picUSA.Click' Display the country namelblMessage.Text = "United States of America"
End Sub
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Microsoft Document Explorer
• The Visual Studio Help, also called Microsoft Document Explorer, contains these options:– How Do I – a task-based topics list by category– Search – find help topics using words/phrases– Contents – displays a table of contents for help– Index – Search using predefined keywords– Favorites help – lets you bookmark help topics– Dynamic help – help for current task performed
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Context-Sensitive Help (F1 Key)
• Displays information about whatever feature the user is currently focused on
• For example:– Click on a Button control– Press F1– Help explains all about the Button control– Click on a Label control– Press F1– Help explains all about the Label control
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Debugging: Compilation Errors
• These are errors in the syntax (form) of your program
• Visual Basic will inform you of these errors as soon as the code is entered
• The area of the error will be underlined with a jagged blue line
• A description of the error will be given in the Error List window
• Display this window by selecting Error List from the View menu option
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Debugging: Runtime Errors
• Some errors occur as your program runs• These are different from syntax errors which
occur as the code is entered by the programmer
• Runtime errors occur when Visual Basic attempts to perform an operation that cannot be executed