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Chapter 6: Using VB .NET Supplied Classes

Chapter 6: Using VB .NET Supplied Classes. Visual Basic .NET Programming: From Problem Analysis to Program Design. Objectives. Learn more about the Framework Class Library Invoke methods in the String class Display message boxes Format numeric output Work with dates

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Chapter 6: Using VB .NET Supplied Classes

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  1. Chapter 6: Using VB .NET Supplied Classes Visual Basic .NET Programming: From Problem Analysis to Program Design

  2. Objectives • Learn more about the Framework Class Library • Invoke methods in the String class • Display message boxes • Format numeric output • Work with dates • Read and write sequential files Visual Basic .NET Programming: From Problem Analysis to Program Design

  3. Introducing the Framework Class Library • Assembly • File with .dll suffix • Contains Intermediate Language (IL) • Framework Class Library • Consists of approximately 100 assemblies • Each containing one or more classes • Organized logically into namespaces Visual Basic .NET Programming: From Problem Analysis to Program Design

  4. Introducing the Framework Class Library (continued) • Namespace • Can contain both classes and other namespaces • System is rootof all other namespaces • Framework compilers do not automatically search all namespaces for classes used by code • Except System namespace • For all other namespaces • Use Imports keyword Visual Basic .NET Programming: From Problem Analysis to Program Design

  5. Visual Basic .NET Programming: From Problem Analysis to Program Design

  6. Invoking Methods in the String Class • String data • Collection of characters • Stringclass • Member of System namespace. • Stored in reference variable • Property • Special kind of VB .NET method • Access like public variable Visual Basic .NET Programming: From Problem Analysis to Program Design

  7. Visual Basic .NET Programming: From Problem Analysis to Program Design

  8. Visual Basic .NET Programming: From Problem Analysis to Program Design

  9. Invoking Methods in the String Class (continued) • String instances in VB .NET are immutable • Cannot be changed • Methods create and return new String • Each character in String instance has index • Indicates position • Index for first character is 0 Visual Basic .NET Programming: From Problem Analysis to Program Design

  10. Visual Basic .NET Programming: From Problem Analysis to Program Design

  11. Using the Length Property • Length property • Contains number of characters in String • To access length for String s1: • s1.length Visual Basic .NET Programming: From Problem Analysis to Program Design

  12. Using the Copy Method • Creates copy of String instance • Returns reference to new instance • Example: • s2 = String.Copy(s1) • Class method • Invoke using class name Visual Basic .NET Programming: From Problem Analysis to Program Design

  13. Using the Chars Method • Returns character located at specified index • Example: • s1.Chars(6) • Instance method • Invoke using reference variable name Visual Basic .NET Programming: From Problem Analysis to Program Design

  14. Using the Equals Method • See if two Stringinstances contain same data • Example: • s1.Equals(s2) • Not same as = Visual Basic .NET Programming: From Problem Analysis to Program Design

  15. Using the Substring Method • Extract one or more characters from a String • Return new String containing extracted characters • Arguments: • Index of first character • Number of characters • Example: • s2 = s1.Substring(0, 5) Visual Basic .NET Programming: From Problem Analysis to Program Design

  16. Using the Replace Method • Replace one or more characters in String • With one or more other characters • Arguments: • String containing character(s) to be replaced • Stringcontaining replacement character(s) • Example: • s2 = s1.Replace(“Hello”, “Hi”) Visual Basic .NET Programming: From Problem Analysis to Program Design

  17. Using the Insert Method • Add one or more characters into existing String • Beginning at specified index • Example: • s2 = s1.Insert(6, “There “) • Arguments: • Index where to begin insertion • Characters to be inserted Visual Basic .NET Programming: From Problem Analysis to Program Design

  18. Using the StartsWith and EndsWith Methods • StartsWith • Compares String with beginning character(s) of another String • Returns True or False • Depending on whether there is a match • EndsWith • Compares ending characters • Use both methods to search for text containing specified characters Visual Basic .NET Programming: From Problem Analysis to Program Design

  19. Using the StartsWith and EndsWith Methods (continued) • StartsWith example: • s1.StartsWith(“Hi”) • EndsWith example: • s1.EndsWith(s3) Visual Basic .NET Programming: From Problem Analysis to Program Design

  20. Using the ToUpper, ToLower, IndexOf, and ToString Methods • Change case of String value to uppercase or lowercase • ToUpper • Uppercase • ToLower • Lowercase Visual Basic .NET Programming: From Problem Analysis to Program Design

  21. Using the ToUpper, ToLower, IndexOf, and ToString Methods (continued) • IndexOf method • Search Stringinstance for specific value • Returns index of first character of value • Or -1 • If no matching value is found • ToString • Convert numeric value to String Visual Basic .NET Programming: From Problem Analysis to Program Design

  22. Displaying Message Boxes • Use message box to • Display message • Get response • MessageBox class • Member of System.Windows.Forms namespace • Single method named Show • Creates instance of MessageBox • Makes it visible Visual Basic .NET Programming: From Problem Analysis to Program Design

  23. Displaying Message Boxes (continued) • Show() method arguments • Message to display • Can string literal or variable • Caption to display • Buttons to display • Type of icon to show Visual Basic .NET Programming: From Problem Analysis to Program Design

  24. Example 6-12: Displaying message boxes 1. ' display a message 2. MessageBox.Show(“Hello Again”) 3. 'display a message and a caption 4. MessageBox.Show(“Hello Again”, “MessageBox Demo”) 5. 'display message, caption, Yes/No/Cancel buttons 6. MessageBox.Show(“Hello Again”, “MessageBox Demo”, MessageBoxButtons.YesNoCancel) Visual Basic .NET Programming: From Problem Analysis to Program Design

  25. Example 6-12: Displaying message boxes (continued) 7. 'display message, caption, Yes/No/Cancel buttons, and Icon 8. MessageBox.Show(“Hello Again”, “MessageBox Demo”, MessageBoxButtons.YesNoCancel, MessageBoxIcon.Information) Visual Basic .NET Programming: From Problem Analysis to Program Design

  26. Visual Basic .NET Programming: From Problem Analysis to Program Design

  27. Displaying Message Boxes (continued) • Button combinations • Automatically displayed by IntelliSense • After you type class name MessageBoxButtons • Select specific buttons to be displayed from list • Icons • Displayed by IntelliSense when typing MessageBoxIcon Visual Basic .NET Programming: From Problem Analysis to Program Design

  28. Visual Basic .NET Programming: From Problem Analysis to Program Design

  29. Visual Basic .NET Programming: From Problem Analysis to Program Design

  30. Displaying Message Boxes (continued) • show() method return value • Data type DialogResult • Compare to specific values using Ifstatement Visual Basic .NET Programming: From Problem Analysis to Program Design

  31. Visual Basic .NET Programming: From Problem Analysis to Program Design

  32. Formatting Numeric Output • Format numeric output to make it: • More attractive • Easier to read • Use ToString method to format numeric data • Argument types: • Format codes • Format mask Visual Basic .NET Programming: From Problem Analysis to Program Design

  33. Visual Basic .NET Programming: From Problem Analysis to Program Design

  34. Formatting Numeric Output (continued) • Format mask examples: • s = phoneNo.ToString(“(###) ###-####”) • s = d.ToString(“$#,##0.00”) • ssNo.ToString(“###-##-####”) Visual Basic .NET Programming: From Problem Analysis to Program Design

  35. Working With Dates • FCL structures: • DateTime • Contains actual date value • TimeSpan • Contains computed difference between two dates • Belong to System namespace Visual Basic .NET Programming: From Problem Analysis to Program Design

  36. Working With Dates (continued) • Today • Property of DateTime • Gets system date • Returns DateTime instance. • Example: • todaysDate = DateTime.Today • Now property • Captures current time Visual Basic .NET Programming: From Problem Analysis to Program Design

  37. Working With Dates (continued) • Format date display • Invoke ToString method • Pass arguments that describe desired format • Creating DateTime instance example: • eleanorsBirthday = New DateTime(1998, 12, 15) Visual Basic .NET Programming: From Problem Analysis to Program Design

  38. Visual Basic .NET Programming: From Problem Analysis to Program Design

  39. Comparing Dates • Subtract() method • DateTime class • Compute number of days between DateTimes • Returns instance of TimeSpan class • TotalDays() method • TimeSpan class • Obtain number of days in TimeSpan Visual Basic .NET Programming: From Problem Analysis to Program Design

  40. Example 6-18: Computing the Difference between Dates 1. ' compute the difference between two dates 2. Dim daysDifference As Double, ageDifference As TimeSpan 3. ageDifference = emilysBirthday.Subtract(eleanorsBirthday) 4. daysDifference = ageDifference.TotalDays() 5. Console.WriteLine(“The age difference is “ & daysDifference) Visual Basic .NET Programming: From Problem Analysis to Program Design

  41. Comparing Dates (continued) • Compare() method • DateTime class • Compares two DateTime instances • Returns either: • -1 • 0 • +1 Visual Basic .NET Programming: From Problem Analysis to Program Design

  42. Performing Arithmetic with Dates • DateTime class • Methods add a value to month, day, or year • Named AddMonths, AddDays, AddYears, etc. • Example: • todaysDate.AddMonths(1) Visual Basic .NET Programming: From Problem Analysis to Program Design

  43. Reading and Writing Sequential Files • Classes typically employed in sequential file processing: • StreamWriter • StreamReader • Database • Data organized into one or more tables • Tables can be related Visual Basic .NET Programming: From Problem Analysis to Program Design

  44. Reading and Writing Sequential Files (continued) • Files • Contain data • Organized into fields and records • Field • Individual data item • Can be contained in a primitive variable or Stringinstance • Record • Consists of one or more related fields Visual Basic .NET Programming: From Problem Analysis to Program Design

  45. Reading and Writing Sequential Files (continued) • File • Contains one or more related records • Sequential file • Data organized with one data item following another • System.IO namespace classes: • StreamWriter • StreamReader. • Must use Imports statement Visual Basic .NET Programming: From Problem Analysis to Program Design

  46. Reading and Writing Sequential Files (continued) • StreamWriter class • WriteLine() method • Can overwrite or append file • StreamReader class • ReadLine() method • Write loop when reading from sequential file • Check for existence of data beforereading data • Use Peek() method Visual Basic .NET Programming: From Problem Analysis to Program Design

  47. Example 6-22: Appending to a Sequential File 1. Dim customerFile As New StreamWriter("C:\Customers.txt", True) 2. customerFile.WriteLine("Graham") 3. customerFile.WriteLine("Marietta") 4. customerFile.WriteLine("467-1234") 5. customerFile.Close() Visual Basic .NET Programming: From Problem Analysis to Program Design

  48. Programming Example: Employee Report • Input • Sequential file named C:\Employee.txt containing employee information • Output • Employee report containing: • 1. Social Security number formatted nnn-nn-nnnn • 2. Date employed formatted as monthname dd, yyyy • 3. Hourly pay rate formatted as currency • 4. Formatted employee name Visual Basic .NET Programming: From Problem Analysis to Program Design

  49. Summary • Visual Basic .NET stores string data in instances of String class • Provides several useful methods and properties • Immutable • MessageBox • Used to display message and get response • Invoke ToString method in primitive structures to format numeric data Visual Basic .NET Programming: From Problem Analysis to Program Design

  50. Summary (continued) • Work with dates using: • DateTime • TimeSpan • VB .NET uses two classes in System.IO namespace to work with sequential files: • StreamWriter • StreamReader Visual Basic .NET Programming: From Problem Analysis to Program Design

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