CIS162AD C

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CIS162AD - C

• Methods, Menus, and Dialog Boxes
• 05_methods_menus.ppt

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Overview of Topics

• Top-Down Design
• Built-in Methods
• Black Box Analogy
• Programmer-Defined Methods
• Methods Signature Overloading
• Pass-by-value Arguments
• Menu Designer
• Context Menus (right-click)
• Common Dialog Boxes

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Top-Down Design

• A design method where the major task to be
  accomplished is divided into subtasks.
• Divide-and-Conquer
• Stepwise Refinement
• The goal is to write a modular program that is
  easier to read and maintain.

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Top-Down Design - Analogy

• A design method where the major task to be
  accomplished is divided into subtasks.
• Major Task clean house
• Subtasks dust, vacuum, sweep, mop
• Programming example.
• Major Task CS5 Sales Calculator
• Subtasks input qty, pricecalculate sales
  tax, shipping, subtotal, etcdisplay total bill

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Subtasks

• Each subtask should perform a single well-defined
  task.
• Each subtask may produce some result.
• Treat them as small programs.
• Input -gt Process -gt Output
• These subtasks can be used at different times in
  one program or placed in a library and used by
  many different programs.
• The int.Parse method is a complicated task that
  converts strings to numbres, and is used by many
  different programs.

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Top-Down Design Implementation

• Top-Down design is implemented using methods.
• A method is a collection of statements that are
  grouped together to perform a specific operation.
• Methods have inputs called arguments.
• Methods can be defined to return no value, but if
  it does return a value, only one value can be
  returned through the return statement.
• Methods can return more than one value through
  call-by-reference arguments (more on this later).
  

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Programmer-Defined Methods

• Before coding some programmer-defined methods,
  lets look at some built-in methods a little
  closer.
• It will help understand what we are trying to
  develop if we look at how methods are used.

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Built-in Methods

• They are like small programs.
• They have their own input process output.
• They can have one or more inputs.
• But methods can only return one output.
• As programmers, we dont get to see the code
  (process) of built-in methods.
• The process is like a black box

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Black Box Analogy

• Many methods are designed as black boxes.
• This means that as programmers we should not be
  concerned how the methods performs its
  processing.
• We only need to know the inputs, outputs, and
  what it does.
• We know what is required to use it, but we dont
  know how it does its calculations. 
• Develop your own methods with the Black Box
  Analogy in mind.

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Convert Text to Integer int.Parse

• Convert Text to Integer method is named
  int.Parse.
• The documentation for int.Parse states the value
  that will be returned, method name, and the type
  and number of arguments. intNumber
  int.Parse(String) returnedValue MethodName
  (arguments)
• Int.Parse takes one argument that is a String.
• The method is called using the following
  syntaxIf txtQuantity.Text contains 3 then
  the function call intNumber
  int.Parse(txtQuantity.Text)would return a value
  of 3 into intNumber.

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Method Call

• We issue a method call when we use it.
• Processing control is passed to the method until
  it completes its task and returns control back to
  the calling method.
• Most methods return a value back,but only one
  value can be returnedthrough the return
  statement.

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Round Method

• Methods can only return one value, but may have
  more than one argument.decWholeNum
  decimal.Round(decNum, 0)
• The value returned is a whole number with no
  digits after the decimal point.

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Methods Signature Overloading

• Method overloading occurs when more than one
  method with the same name is defined, but differ
  in the parameter list.MessageBox.Show(TextMessag
  e)MessageBox.Show(TextMessage,
  TitleBar)MessageBox.Show(TextMessage, TitleBar,
  ButtonType)MessageBox.Show(TextMessage,
  TitleBar, ButtonsType, Icon)
• Each methods signature is unique and consists
  of
• Method name
• The number, data types, and order of its
  parameters
• Parameters can also be modified with the keywords
  ref and out (These keywords are covered in next
  powerpoint presentation)
• The signature does NOT include the data type of
  the returned valueand the names used to identify
  the parameters.

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Small Programs

• Think of each method as a small program with
  input, process, and output steps. Output
  lt Process lt Input
• returnedValue MethodName (arguments)
• intNumber int.Parse(String)

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Programmer-Defined Methods

• The single value that a method returns can be a
  string or numeric.
• Two Components 1. Method Definition 2. Method
  Call

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Function Definition - Syntax

• Syntaxprivate dataType MethodName(arguments)
  statement(s) return expression
• dataType is where we specify what type of value
  is being returned, string or numeric.
• Use the return statement to return the value.
• Variables that will be used to store the values
  sent into the method are listed in parentheses as
  arguments.

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Method Definition - Example

• private decimal calcExtendedPrice(int intQty,
  decimal decPrice) decimal decExtendedPrice
  decExtendedPrice intQty decPrice return
  decExtendedPrice
• decimal is the data type of the value being
  returned.
• calcExtendedPrice is the Method Name.
• intQty and decPrice are the arguments passed to
  method.
• The signature of this method is
  calcExtendedPrice(int, decimal)

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Return Statement

• Return statement returns the value back to the
  variable listed to the left of the equal sign on
  the call statement.
• Return statement returns processing control back
  to the calling procedure.
• Only one value can be returned.
• Variable data type of returned value must match
  the return type specified in heading.

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Multiple Returns

• A method may be defined with multiple Return
  statements.
• The first Return statement executed returns the
  value and returns processing control back to the
  calling procedure.
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice if (intQty lt 26) return
  intQty decPrice else return intQty
  (decPrice .95) //5 discount

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Single Return Preferred

• Although methods can be coded using multiple
  Return statements, one Return statement is
  preferred.
• Having multiple Returns in complex procedure can
  be difficult to maintain and debug.
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice ) decimal decExtendedPrice
  if (intQty lt 26) decExtendedPrice intQty
  decPrice else decExtendedPrice intQty
  (decPrice .95) //5 discount return
  decExtendedPrice

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A Method without a Return

• If a method that is supposed to return a value
  does not contain a return statement, then the
  compiler will generate a syntax error.
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice ) decimal decExtendedPrice
  if (intQty lt 26) decExtendedPrice intQty
  decPrice else decExtendedPrice intQty
  (decPrice .95) //return decExtendedPrice
  //commented out syntax error

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Method Call

• The method call is issued when the method is used
  in another method.private void
  btnCalculate_Click() intQty
  int.Parse(txtQuantity.Text) decPrice
  decimal.Parse(txtPrice.Text) decExtendedPrice
  calcExtendedPrice(intQty, decPrice)

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Local Variables

• Variables are local to the method in which they
  are defined.
• Variables defined in a particular method are
  assigned their own memory and can only be
  referenced in that method.
• Variables defined in calcExtendedPrice( ) are
  assigned their own memory and can only be
  referenced in calcExtendedPrice( ).
• Different methods cannot see or reference each
  others variables.
• They have separate memory allocations even though
  the variable names may be the same.

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Passing Arguments

• private void btnCalculate_Click() int
  intQty decimal decPrice, decExtendedPrice
  intQty int.Parse(txtQuantity.Text) decPrice
  decimal.Parse(txtPrice.Text) decExtendedPrice
  calcExtendedPrice(intQty, decPrice)
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice) decimal decExtended decExt
  ended intQty decPrice return decExtended

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Declare Variables
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Input Values
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decExtendedPrice calcExtendedPrice(intQty,
decPrice)
Pass-by-Value - Values in variables of
btnCalculate are sent to variables of
calcExtendedPrice.
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Methods Use Local Variables

• private void btnCalculate_Click() int
  intQty decimal decPrice, decExtendedPrice
  intQty int.Parse(txtQuantity.Text) decPrice
  decimal.Parse(txtPrice.Text) decExtendedPrice
  calcExtendedPrice(intQty, decPrice)
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice) decimal decExtended decExt
  ended intQty decPrice return decExtended

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decExtended intQty decPrice
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Returning Method Values

• private void btnCalculate_Click() int
  intQty decimal decPrice, decExtendedPrice
  intQty int.Parse(txtQuantity.Text) decPrice
  decimal.Parse(txtPrice.Text) decExtendedPrice
  calcExtendedPrice(intQty, decPrice)
• private decimal calcExtendedPrice(int intQty,
  decimal decPrice) decimal decExtended decExt
  ended intQty decPrice return decExtended

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decExtendedPrice calcExtendedPrice(intQty,
decPrice)
Return statements sends the value to variable on
the left side of the equal sign on the method
call statement.
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Menu Designer

• Plan menu options / paths.
• Add MenuStrip control to component tray.Just
  like the ToolTip.
• Enter Text for menu item in box labeled Type
  Here.
• Use ampersands to define control keys.
• Name menu items using menu path and mnu prefix.
• Need to know name so we can tell which menu item
  was selected in the code.private void
  mnuFileExit_Click(object sender, System.EventArgs
  e) this.Close()

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Menu Designer Example
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Context Menus

• Context menus are shortcut menus that pop up with
  a right-click.
• Add a ContextMenuStrip control to the component
  tray.
• Use the Menu Designer to add items.
• More than one context menu can be added.
• In order to make the context menu available to
  users, it must be assigned to the form or control
  by using the ContextMenuStrip property.
• See the images on the next two slides

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Context Menu Example
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Assign Context Menu to Form
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Common Dialog Boxes

• Common dialog boxes available
• FontDialog
• ColorDialog
• OpenFileDialog
• SaveFileDialog
• PrintDialog
• PrintPreviewDialog

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Common Dialog Boxes

• The Common Dialog Box controls can save
  programmers the time and trouble of designing
  custom dialog boxes for common purposes.
• Add a common dialog box control to the component
  tray.
• The default Name of the Dialog maybe used, unless
  more than one is being used in the
  program.. colorDialog1, fontDialog, etc.
• You wont see anything in design time, because
  the dialog box is displayed at run-time with
  code.
• Use the ShowDialog method to display a dialog
  box. fontDialog1.ShowDialog( ) colorDialog1.Sh
  owDialog( )

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FontDialog Box
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Using Selected Options

• Dialog Boxes are objects themselves with
  properties.
• The values selected by users in a font or color
  dialog box are stored in the dialog boxs
  properties.
• The values in the dialog boxes selected by users
  need to be applied to controls on the
  form. lblGrandTotal.Font fontDialog1.Font lb
  lGrandTotalForeColor colorDialog1.Color
  Note property on Labels and Textboxes is
  ForeColor.
• Before showing a dialog box, you should assign to
  it the current value selected just incase users
  click on Cancel. fontDialog1.Font
  lblGrandTotal.Font

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Method Example

• private void mnuEditFont_Click(object sender,
  System.EventArgs e)
• //Initialize the font in the dialog box to the
  current font
• fontDialog1.Font lblGrandTotal.Font
• //Display dialog box so user can pick a font
• fontDialog1.ShowDialog()
• //Apply the font chosen to the Totals section
• lblGrandTotal.Font fontDialog1.Font
• lblNumberOfOrders.Font fontDialog1.Font
• lblAverageOrder.Font fontDialog1.Font

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Summary

• Top-Down Design
• Built-in Methods
• Black Box Analogy
• Programmer-Defined Methods
• Methods Signature Overloading
• Menu Designer
• Context Menus
• Common Dialog Boxes