1. Computer Programming Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology andres@dlit.edu.tw http://www.cse.dlit.edu.tw/~andres

2. 2 Chapter 5 Event-Driven Input and Software Design Strategies

3. 3 Chapter 5 Topics Declaring and Instantiating a TextBox Declaring and Instantiating a Button Handling Button click events l Converting strings into numeric types l Using the object-oriented design (OOD) strategy l Using CRC cards l Using the Functional Decomposition strategy l Using Pseudocode

4. 4 Interface An interface is a connecting link at a shared boundary that allows independent systems to meet and act on or communicate with each other. Interface computerprogrammer shared boundary (screen)

5. 5 Event-Driven Programming l VB.NET uses event-driven programming. ( 事件驅動 ) The user’s interaction with a GUI component is an event that can be processed by the program. l To do so, the programmer must write code inside an event-handling method that is pre-defined in Visual Studio.NET

6. 6 Event Handling (p.110) Window Closing Opened … Mouse Moved Dragged Clicked … Key Pressed Rleased Protected Overloads Overrides _ Sub Dispose (ByVal disposing _ as Boolean) ……… End Sub Public Class Form1 Inherits System.Windows.Forms.Form Private Sub New (.... )... End Class Firing a event Events Event handler Program to Hold

7. 7 Graphical User Interfaces l GUIs are built from GUI components (also called widgets for window gadgets). l GUI component classes are part of System.Windows.Forms.Form (Abstract Windowing Toolkit package). l GUIs are event-driven. They generate events when the user interacts with the GUI. l An event is an action such as clicking the mouse, clicking a button, that takes place asynchronously (not at a particular time) with respect to the execution of the program.

8. 8 Some GUI components Form A kind of window in which components can be placed. Label A component where text can be displayed. Button A component that generates an event when the user clicks on it with the mouse. TextBox A component in which the user can type a value. The user must first place the cursor in the field by clicking inside the field.

9. 9 Some of the VB.NET Objects Hierarchy Component ButtonLabelTextBoxBase TextBox Object

10. 10 More of the VB.NET Object Hierarchy Object System.Windows.Forms System.Windows.Forms.Form System.Windows

11. 11 Steps for using a Windows Form 1 Open a new Windows Application project 2. Add output control to the default for (such as a label) 3. Assign data to the output control in an appropriate event 4. Run the application

12. 12 Public Class Form1 Inherits System.Windows.Forms.Form... Private Sub Form1_Load (.... ) Label1.Text = “Total is $” & total End Sub End Class Writing Code for a Form

13. 13 class Private data and methods New Dispose

14. 14 Syntax for Instance Method Call. InstanceMethodCall ObjectName. MethodName ( parameter, parameter... ) EXAMPLES Mybase.New() Console.WriteLine (“Good morning.”)

15. 15 2 Steps for processing an event lAdd code template for event by double- clicking control which triggers event lWrite code in event method

16. 16 Handling a window event l Window controls have pre-defined events for handling most events occurring during a Windows application l Custom events can be created l Events are found by double-clicking the control that generates event

17. 17 Form Methods l Every form has two methods that are part of the class : New and Dispose l The New method calls methods from the Form base class to create a Form instance. l The Dispose method calls another Dispose method to remove all components from the form and to close the form

18. 18 New Method Public Sub New() MyBase.New ' This call is required by Windows Form Designer InitializeComponent() ' Other code can go here End Sub

19. 19 Dispose Method Protected Overloads Overrides Sub Dispose_ (ByVal disposing As Boolean) If disposing Then If Not (components Is Nothing) Then components.Dispose( ) End If MyBase.Dispose (disposing) End Sub

20. 20 Public Class Form1 Inherits System.Windows.Forms.Form Const MONTH_NAME As String = "August" 'The name of the month Const MONTH_NUMBER As String = "8" 'The number of the month Const DAY As String = "18" 'The day of the month Const YEAR As String = "2001" 'The four-digit year Dim first As String 'Date in Month day, year format Dim second As String 'Date in day Month year format Dim third As String 'Date in mm/dd/yyyy format Dim fourth As String 'Date in dd/mm/yyyy format #Region "Windows Form Designer generated code" Case Study : DateFormats Program

21. 21 Public Sub New() MyBase.New() 'This call is required by the Windows Form Designer InitializeComponent( ) 'Create date formats and display on screen first = MONTH_NAME & " " & DAY & ", " & YEAR lblFirst.Text = first second = DAY & " " & MONTH_NAME & " " & YEAR lblSecond.Text = second third = MONTH_NUMBER & "/" & DAY & "/" & YEAR lblThird.Text = third fourth = DAY & "/" & MONTH_NUMBER & "/" & YEAR lblFourth.Text = fourth End Sub

22. 22 'Form overrides dispose to clean up the component list. Protected Overloads Overrides Sub Dispose(ByVal_ disposing As Boolean) If disposing Then If Not (components Is Nothing) Then components.Dispose() End If MyBase.Dispose(disposing) End Sub #End Region End Class

23. 23 5.2 Using Button and TextBox Button – A Component of a form that fires an event when the user clicks on it with the mouse Text box- A component of a form in which the user can type a value. The user must first place the cursor in the text box by clicking inside the box (see Figure 5.2 on page 169 of your textbook)

24. 24 5.3 Adding a Text Box to a Form 1.Put a textbox on the form 2. Set the appropriate properties for the textbox

25. 25 5.4 Extracting a Value From a Text Box textContents = inputBox.Text InputBox.Text = “Replace me “ lblLabel1.Text = “Enter more data: ”

26. 26 5.5 Steps for using a Button 1.Add a button to the form 2.Set appropriate properties for the button 3.Write code for button’s Click event

27. 27 'Button’s name is Done Private Sub Done_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles Done.Click End Sub 5.6 A Button’s Click Event

28. 28 Handling A Button Click Event 'Button’s name is Done Private Sub Done_Click(... ) 'Code goes here End Sub

29. 29 CopyString Program l Textbox Name: inputField l Textbox Font : 10 point, Bold l Textbox Text: “ “ l Textbox Name: outputLabel l Textbox Font : 10 point, Bold l Textbox Text: “ “ l Label Name: entryLabel l Label Font : 10 point, Bold l Label Text: Enter a string:] l Button Name: button1 l Button Text: Copy

30. 30 CopyString Program Public Class Form1 Inherits System.Windows.Forms.Form #Region " Windows Form Designer generated code " Public Sub New() MyBase.New() ' This call is required by the Windows Form Designer. InitializeComponent() 'Add any initialization after the InitializeComponent() call End Sub

31. 31 ' Form overrides dispose to clean up the component list. Public Overloads Sub Dispose() MyBase.Dispose() If Not (components Is Nothing) Then components.Dispose() End If End Sub......... Private Sub button1_Click(ByVal sender As System.Object, _ ByVal e AsSystem.EventArgs) Handles enter.Click ' Copies the text from the box to the label outputLabel().Text = inputField().Text End Sub End Class

32. 32 5.8 Converting a String to a Numeric Value l Predefined class Built-inObject Type IntegerInt32 LongInt64SingleDoubleChar

33. 33 Converting a String to a Numeric Value Dim someDouble As Double someDouble = Double.Parse (“37.89”) Dim intNumber As Integer intNumber = Int32.Parse (priceField.Text)

34. 34 5.10 Software Design Strategies FUNCTIONAL OBJECT-ORIENTED DECOMPOSITION DESIGN The solution is expressed in terms of objects (self-contained entities composed of data and operations on that data) that interact by sending messages to one another. The problem is divided into more easily handled subproblems, the solutions of which together create a solution to the overall problem.

35. 35 5.11 What is an object? OBJECT set of methods (public member functions)...... Private data and methods internal state (values of private data members)

36. 36 5.12 Object-Oriented Design A technique for developing a program in which the solution is expressed in terms of objects -- self- contained entities composed of data and operations on that data. Text Copy...... Clear Private data and methods New Dispose...... Show Private data and methods TextBox Form

37. 37 More about OOD l Languages supporting OOD include: VB.NET, Java, Smalltalk, Eiffel, CLOS, and Object-Pascal. l A class defines the pattern used when instantiating an object of that type. l A class generally contains private data and public operations (called methods).

38. 38 5.13 Functional Decomposition A technique for developing a program in which the problem is divided into more easily handled subproblems, the solutions of which create a solution to the overall problem. In functional decomposition, we work from the abstract (a list of the major solution steps for which some implementation details remain unspecified) to the concrete (algorithmic steps for which the implementation details are fully specified).

39. 39 Functional Decomposition FOCUS is on the sequence of actions (algorithms) required to solve the problem. BEGINS by breaking the solution into a series of major steps. This process continues until each subproblem cannot be divided further or has an obvious solution. PROGRAMS are collections of modules that solve subproblems. A module structure chart (hierarchical solution tree) is often created. DATA plays a secondary role in support of actions.

40. 40 Find Weighted Average Print Weighted Average Module Structure Chart Main Print Data Print Heading Get Data Prepare File for Reading

41. 41 Two Design Strategies FUNCTION OBJECT.................. FUNCTIONAL OBJECT-ORIENTED DECOMPOSITION DESIGN

42. 42 Case Study : Rainfall Program Variables: NameData Type Form1Form entryLabelLabel outputLabelLabel inputTextTextbox enterButton totalDouble numberEntriesDouble AmountDouble averageDouble

43. 43 Rainfall Program Public Class Form1 Inherits System.Windows.Forms.Form Dim amount As Double ' Holds input value Dim average As Double ' Holds computer average Dim total As Double ' Keeps running total Dim numberEntries As Double ' Keeps count of entries #Region " Windows Form Designer generated code " Public Sub New() MyBase.New() ' This call is required by the Windows Form Designer. InitializeComponent() 'Add any initialization after the InitializeComponent() call End Sub

44. 44 ' Form overrides dispose to clean up the component list. Protected Overloads Overrides Sub Dispose(ByVal disposing As_ Boolean) If disposing Then If Not (components Is Nothing) Then components.Dispose() End If MyBase.Dispose(disposing) End Sub Private Sub Form1_Load(ByVal sender As System.Object, ByVal e_ AsSystem.EventArgs) Handles MyBase.Load total = OR numberEntries = OR End Sub

45. 45 Private Sub enter_Click(ByVal sender As System.Object, _ ByVal e AsSystem.EventArgs) Handles enter.Click ' Convert string in inputText to a double value amount = CDbl(inputText.Text) numberEntries += 1 ' Increment entries total = total + amount ' Add value to sum average = total / numberEntries ' Compute average outputLabel.Text = average ' Display average inputText.Text = "" ' Clear input text box End Sub End Class

46. 46 Exercises l Chapter4 n Exam preparation exercises: 1, 4( 計算過程 ),5, 9 n Programming warm-up exercises: 3 l Chapter5 n Quick Check: 2, 6, 7, 8, 9 n Exam preparation exercises: 4,9 n Programming warm-up exercises: 1, 2, 3 l Due Date: 10/21 ( 四 ) l 請將題目翻譯成中文 l 請寫在 A4 報表紙上，勿使用電腦列印