objects, classes, and hierarchies 1: windows and menus

1
objects, classes, and hierarchies 1windows and
menus
2
The story up until now

• Everything in your computer is data
• Including programs
• Data is divided into objects
• Objects can be inside of other objects
• Boxes inside groups
• Colors inside bitmaps
• Objects have types (or classes)
• Procedures
• Numbers (1, -3.5)
• Strings (this is a string, blue)
• Bitmaps
• Picture objects (lines, groups, boxes, etc.)

3
Looking inside data objects
Ellipse Width 15 Height 10

• Data objects are like forms
• They have fields (aka members)
• Filled in by values
• The fields
• Have names (Width, Height)
• The fields are filled in by other data objects
• The objects type (Box, Color) determines what
  fields it has

Box Width 10 Height 10
Number Value 10
Procedure Name iterated-group Arguments proc
count Body apply group
up-to count proc
Color R 240 G 220 B 0
4
Member notation
Ellipse Width 15 Height 10

• You can ask for a field of a data object using
  the . notation object.memberName
• myColor.R
• pixel myBitmap 0 0.R
• iterated-group.Name
• iterated-group.Arguments
• mybox.Width
• Note to simplify the presentation, Ive lied
  here about what the actual fields of boxes,
  procedures, etc. are.
• You can find out what fields are really in an
  object using the inspector.

Box Width 10 Height 10
Number Value 10
Procedure Name iterated-group Arguments proc
count Body apply group
up-to count proc
Color R 240 G 220 B 0
5
Types and subtypes
Object

• Types often have subtypes
• Integers are a subtype of numbers
• Boxes are a subtype of Pictures
• All types are subtypes of the magic type Object
• Subtyping means objects can have many types
• All Integers are also Numbers
• All Boxes are also Pictures
• And all objects are Objects

List
Number
Array
Integer
Float
Picture
Box
Line
Group
6
Example 1The Windows Forms class hierarchy
Control

• User-interface components (windows, buttons,
  etc.) are all objects
• Individual windows are Form objects
• Individual elements of windows are objects of
  type Button, TextBox, Label, etc.
• Form, Button, etc. are all subtypes of the type
  Control
• Controls can have other Controls inside of them
• Which is how buttons can be inside forms
• All these classes are in the System.Windows.Forms
  namespace

Form
TextBox
Button
TrackBar
Label
PictureBox
Greatly simplified version of the winforms class
hierarchy
7
Wait a minute, whats a class?

• For our purposes, we can think of it as a synonym
  for type
• In C, Java, and .NET, classes are a kind of
  type
• Have fields
• Have methods (essentially fields that hold
  procedures)
• Fields and methods of an object are determined by
  its class
• Objects of the same class have the same fields
  and methods (procedures that seem like fields)
• But not necessarily the same values for the fields

8
Fields of the Control class

• These can be used to change the appearance of any
  control
• There are many more, but these should be enough
  for you for now.

• BackColor, ForeColor
• Background/foreground color for the control
• Font
• Font that text appears in (see the slide at the
  end for how to specify a font)
• Text
• Text that appears in the control (if any)
• Height, Width
• The size of the control
• Location
• The X,Y coordinate of the top-left corner (as a
  point)
• Left, Top
• The individual X- and Y- coordinates of the
  control within its window

9
Member procedures (aka methods)

• Some of an objects members are procedures
• They act like theyre stored inside the object
• You call them by saying object.name args
• They are usually called methods
• N.B. method is also used to refer to a
  slightly different kind of procedure well talk
  about in the next unit
• Examples
• x.ToStringReturns a string that represents x
• g.DrawLine startx starty endx endyDraws a line
  in a window given its

10
Class-based inheritance

• When a class is a subtype of another class it
  automatically has
• All the fields of the parent class
• All the methods of the parent class
• We say that the subclass inherits the fields and
  methods of the parent class

11
The Form class

• A form is a window that can hold controls
• Its also a subclass of Control, so it has all
  the standard fields of controls
• E.g. Width, Height, BackColor, etc.

• using System.Windows.Forms
• Tells system to use classes in the Windows Forms
  namespace
• new Form
• Makes a form
• form.Controls.Add control
• Adds a control to a form
• Application.Run form
• Displays form and lets the user work with it
  until they close it.
• form.Show
• Used to show a new form after Application.Run has
  already been invoked

12
Creating new data objects

• new type arguments
• Creates a new object of the specified type
• The arguments depend on the type
• For windows forms classes, they generally dont
  take any arguments
• Great, but how do we get at the data in the
  object?

• ? define my-form new Form

13
The TextBox control

• new TextBox
• Makes a space where the user can type
• Whatever they type appears in the Text field of
  the object (remember the Text field?)
• Again, has all the standard fields of a Control

14
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

15
Example entering text

• define get-text starting-textwith f new
  Form make the form tbox
  new TextBox f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

16
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox make the
  text box f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

17
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox add the text box
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

18
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text set its
  text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

19
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150 and width
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text

20
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10 and
  location
• Application.Run f
• tbox.Text

21
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
  give it to the user
• tbox.Text

22
Example entering text

• define get-text starting-textwith f new
  Form tbox new TextBox
  f.Controls.Add tbox
• tbox.Text ? starting-text
• tbox.Width ? 150
• tbox.Location ? point 10 10
• Application.Run f
• tbox.Text
  return the text

23
The make command

• You will find that you spend a lot of time
  calling new and then setting fields of the
  resulting object
• This can be tedious
• And hard to read
• The make command simplifies this by letting you
  simultaneously
• Make the object, and
• Set its fields

• make Type args field value
• Runs new Type args
• Then sets each field of the new object to its
  corresponding value
• N.B. the colons are mandatory

24
Rewriting using make

• define get-text starting-textwith f new
  Form tbox make TextBox
  Text starting-text
  Width 150
  Location point 10 10
• f.Controls.Add tbox
• Application.Run f
• tbox.Text

25
Aside macros and syntactic sugar

• Make is an example of a macro
• Macros are convenient shorthands for more
  complicated expressions
• Meta translates make into a call to new and a
  bunch of assignment statements (well, almost)
• Why are we telling you this?
• Because it means that if you use make incorrectly
• You probably wont see make anywhere in the
  debugger
• Youll see a call to new instead
• So we just dont want you to be confused
• If you want to learn to write your own macros,
  talk to Ian

• Some macros you may have been using
• when test expressions unless test
  expressions
• Gets translated toif test begin expressions
  , or if not test begin expressions ,
  respctvly
• cond test1 expressions test2
  expressions etc
• Gets translated toif test1 begin
  expressions if test2 begin
  expressions etc
• define name args expressions
• Gets translated todefine name args ?
  expressions

26
Three problems

• This is okay, but it has some definite problems
• You click the close box to finish (rather than an
  OK box)
• It doesnt actually work because Application.Run
  turns out to clear the Text of tbox
• Well ignore this for the moment and pretend it
  works
• The window is outrageously tall
• Well leave fixing this as an exercise for the
  reader
• The window has no name
• You can fix this by setting its Text or Name field

27
Adding a button

• define get-text starting-textwith f new
  Form tbox make TextBox
  Text starting-text
  Width 150
  Location point 10 10 b
  make Button Text
  OK Location point
  170 10
• f.Controls.Add tbox
• f.Controls.Add b
• Application.Run f
• tbox.Text

28
Trying it out

• Hey! We have a button!
• Hey! It doesnt do anything!
• Hey! The window is still too tall and has no
  name!
• Oh, shut up

29
Event handling

• You need some way of specifying what to do when
  the button is pressed
• This is done by specifying a procedure called an
  event handler or a callback
• When the even happens, the system calls the
  procedure

30
Event handling in Meta

• Events look like lists of procedures to call when
  the event happens
• To add a handler for an event, add it to the
  list
• object.event ? handler-procedure
• Or specify it as part of the make arguments
• Note Windows Forms always passes two parameters
  to the handler procedure
• The control that generated the event
• An extra data object that well ignore for the
  moment

31
Adding a Click handler

• define get-text starting-textwith f new
  Form tbox make TextBox
  Text starting-text
  Width 150
  Location point 10 10 b
  make Button Text
  OK Location point
  170 10 Click ignore
  ignore ? f.Close
• f.Controls.Add tbox
• f.Controls.Add b
• Application.Run f
• tbox.Text

32
Shortening the form

• define get-text starting-textwith f make
  Form Height 75
  tbox make TextBox
  Text starting-text
  Width 150
  Location point 10 10 b make
  Button Text OK
  Location point 170 10
  Click ignore ignore ?
  f.Close
• f.Controls.Add tbox
• f.Controls.Add b
• Application.Run f

33
Naming the form

• define get-text starting-textwith f make
  Form Height 75
• Text Please enter
  some text tbox make TextBox
  Text starting-text
  Width 150
  Location point 10 10
  b make Button Text
  OK Location point
  170 10 Click ignore
  ignore ? f.Close
• f.Controls.Add tbox
• f.Controls.Add b
• Application.Run f

34
It works!

• In particular, clicking the OK box
• Closes the form as if the user had clicked the
  close box
• Which causes Application.Run to finish
• Which causes get-text to finish and return the
  text

35
The TrackBar control

• new TrackBar
• Makes a slider control
• Useful fields (plus Controls fields)
• Value
• The current numeric value the user has chosen
• Minimum, Maximum
• The numeric values for the ends of the range of
  the slider
• TickFrequency
• How often to draw tick marks
• Orientation
• Whether it should be a horizontal or vertical
  control.Set it to either Orientation.Horizontal
  or Orientation.Vertical.
• Useful events
• ValueChanged (called when the user moves the
  slider)

36
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

37
What does this do?

• with f new Form
  make a form r make TrackBar Top 10 g
  make TrackBar Top 60 b make TrackBar
  Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

38
What does this do?

• with f new Form r make TrackBar
  Top10 make three sliders to go
  with it g make TrackBar Top 60 b
  make TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

39
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
  run this procedure
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

40
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
  on r, g, and b
• Application.Run f

41
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
  add the slider to the
  form
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

42
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
  make it 255 pixels wide
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

43
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
  set its limits to 0 and 255
  
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

44
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  add the following handler for
• 
  when the slider changes
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

45
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore arguments
  and change the background color
  of the form ignore ignore
  ? f.BackColor ? color
  r.Value g.Value b.Value
• list r g b
• Application.Run f

46
What does this do?

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f
  start the form up

47
Running it
48
Fixing a bug

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

This what it looks like when you start it up.
Whats wrong with this?
49
Fixing a bug

• with f new Form r make TrackBar Top
  10 g make TrackBar Top 60 b make
  TrackBar Top 110
• f.BackColor ? color 0 0 0
• for-each slider ?
• f.Controls.Add slider
• slider.Width ? 255
• slider.Minimum ? 0
• slider.Maximum ? 255
• slider.ValueChanged ?
  ignore ignore ?
  f.BackColor ? color r.Value
  g.Value b.Value
• list r g b
• Application.Run f

50
What does this do?

• define slider-text
• with f new Form
• s make TrackBar
  Top 10
  ValueChanged i i ? t.Text ? to-string
  s.Value
• t make TextBox
  Top60 TextChanged
  i i ? s.Value ? System.Int32.Parse t.Text
• f.Controls.Add s
• f.Controls.Add t
• Application.Run f
• Hints
• System.Int32.Parse string returns the number
  represented by string.Example
  System.Int32.Parse 10 returns 10 (the
  integer, not a string)

51
Fixing a bug

• define slider-text
• with f new Form
• s make TrackBar
  Top 10
  ValueChanged i i ? t.Text ? to-string
  s.Value
• t make TextBox
  Top60 TextChanged
  i i ? ignore-errors
  ? s.Value ?
  System.Int32.Parse t.Text
• f.Controls.Add s
• f.Controls.Add t
• Application.Run f
• Ignore-errors runs its argument procedure and
  ignores any errors that occur
• Since ? expressions looks funny, you can also
  say expressions

52
It works!
53
Some other useful Controls

• new Label
• Like a textbox but the user cant change it
• new CheckBox
• Makes a box
• Useful fields
• Checked (whether the box has been checked (true
  or false))

54
Some other useful Controls

• new PictureBox
• Lets you show pictures
• Useful fields
• Width, Height, LocationSame as any other form
• ImageThe image to show. You make an image by
  saying new Bitmap file where file is a
  pathname for a .jpg or other image file.
• SizeModeControls how to scale the size of the
  picture. Set to
• PictureBoxSizeMode.AutoSizeTo make it scale
  images to fit the window (this doesnt actually
  seem to work for me)
• PictureBoxSizeMode.StretchImageTo make it
  stretch/squish image to exactly fit the window
  (this may change the aspect ratio of the image).

55
Another useful component

• make Timer Interval
  time-in-milliseconds Enabled true
  Tick ignore ignore ? code
• Creates a timer object that runs code every
  time-in-milliseconds
• Not actually a type of Control, so dont try to
  add it to a form

56
appendix

• picky little details I ignored

57
Object-oriented programming terminology

• Object
• Any piece of data
• Has type, members (e.g. fields)
• Type
• Determines what kinds of members an object has
• Class
• Essentially means type
• Subclass
• A class that inherits all the members of its
  parent class

• Member
• Data (including procedures) associated with
  objects
• Fields, Methods, Events, Properties
• Field
• Little variable inside an object
• Holds a data value
• Method
• Essentially a field that holds a procedure
• Event
• Essentially a field that holds a list of
  procedures

58
How do I specify a font?

• Just type
• new Font fontfamily
  System.Convert.ToSingle size style
• where
• Fontfamily is a string, like Times New Roman
• Size is a number (the size of the font in
  points), e.g. 10 or 12
• Style is one of
• FontStyle.Regular, FontStyle.Bold,
  FontStyle.Italic, FontStyle.Strikeout,
  FontStyle.Underline

59
How do we fix get-text to return the stupid text?

• Change
• with f new Form
• b new Button
• tbox new TextBox
• bla bla bla
• Application.Run f
• tbox.Text

• To
• with f new Form
• b new Button
• tbox new TextBox
• remember starting-text
• bla bla bla
• tbox.TextChanged ? ignore ignore ?
  remember ? tbox.Text
• Application.Run f
• remember

We add a new event handler that runs whenever the
user changes the text