VB Event driven Programming Timers

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VB Event driven ProgrammingTimers Motion,
Sub Function

• Arif Zaman

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Form Properties

• Caption, Font
• Name (dont change after starting programming)
• Top, Left, Width, Height
• ScaleWidth, ScaleHeight (are very useful to
  measure the actual working area of the form).
  They can also be used to set up convenient
  co-ordinates (read on your own).
• MousePointer (HourGlass)

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Graphics

• AutoRedrawTRUE (if graphics)
• DrawWidth
• DrawMode (read on your own)
• DrawStyle
• FillColor
• FillStyle

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Event Driven Programming

• Up till now the programmer user.
• Essential to learn USER oriented programming.
• A waiter provides the menu and then waits for
  instructions. The customer (user) may want the
  after-dinner mint first, and the appetizer at the
  end.
• We respond to user events.

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Some Events

• Click, DblClick
• KeyDown, KeyPress, KeyUp
• MouseDown, MouseMove, MouseUp
• ReSize (Should reposition and resize things
  appropriately)

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Counting Clicks

• Private Sub Form_Click()
• n n 1
• Print n
• End Sub

• You would expect to get different numbers every
  time you click.
• What happened?
• Debug by putting a breakpoint.

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Global - Local Variables

• Dim variable at the top creates global variables.
• Other variables are local, They are created when
  a sub is started, and discarded at the end.
• Forms (and their properties) are global.
• Try adding the line
• Dim n
• to the top of the previous program. Now it
  works.

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This works

• Private Sub Form_Click()
• Form1.Left Form1.Left 50
• End Sub

• Because Form.Left is global

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Buttons

• If you want to click other things besides forms,
  you can make buttons.
• Caption, Font (others just like form)
• Events Click, MouseDown, MouseMove
• You can mess around with
• Picture, Style (graphical)
• DisabledPicture, DownPicture
• MaskColor and UseMaskColor.

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How to keep Tariq busy all day

• Make a button called Command1 on a form called
  Form1, with a caption Hit Me.
• Private Sub Command1_MouseMove(Button As Integer,
  Shift As Integer, X As Single, Y As Single)
• Command1.Top Rnd (Form1.ScaleHeight -
  Command1.Height)
• Command1.Left Rnd (Form1.ScaleWidth -
  Command1.Width)
• End Sub
• Private Sub Command1_Click()
• Command1.Caption "You Win"
• End Sub

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Your own Sub Function

• Just copy the format Private Sub MySub
• Remember variables will be local unless
  explicitly made global
• Subs can have arguments.
• Functions can return ONE value.

• Private Function ConvertX(x)ConvertX x _
  Form1.ScaleWidth
• End Function
• Private Function ConvertY(y)
• ConvertY (1-y) _ Form1.ScaleHeight
• End Function
• Command1.Left ConvertX(0.5)
• Command1.Top ConvertY(0.9)

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Slide a button to the left

• We want a continuous sliding motion. Try
• Private Sub Command1_Click()
• For i 0 To 5000
• Command1.Left i
• Next i
• End Sub

• Slow it down by
• Private Sub Command1_Click()
• For i 0 To 500000
• Command1.Left i/100
• Next i
• End Sub

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Do it Right use a Timer

• Double click the clock icon (timer). This is a
  control that has no visible appearance on the
  form.
• Set the interval property to 4 and perhaps
  disable it to start off.

• Private Sub Timer1_Timer()
• Command1.Left _ Command1.Left 10
• If Command1.Left 5000 Then
• Timer1.Enabled False
• End If
• End Sub
• Private Sub Command1_Click()
• Command1.Left 0
• Timer1.Enabled True
• Timer1.Interval 4
• End Sub

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A Bouncing Ball

• Position changes by the velocity every time.
• Velocity increases by a fixed amount every time.
• When you hit the ground, you bounce. Velocity
  becomes negative. Position becomes positive.

• Height Form.ScaleHeight- radius of ball
• PosX PosX VelX
• PosY PosY VelY
• VelY VelY 10
• If PosXgtHeight Then
• VelY -VelY
• PosX 2Height PosX
• End If

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Slightly Non-Physical

• Dim VelX
• Dim VelY
• Dim Ht
• Dim Wd
• Private Sub Form_Load()
• VelX 25
• VelY 0
• Ht Form1.ScaleHeight - Shape1.Height
• Wd Form1.ScaleWidth - Shape1.Width
• Timer1.Interval 20
• Timer1.Enabled True
• End Sub

• Private Sub Timer1_Timer()
• Shape1.Top Shape1.Top VelY
• Shape1.Left Shape1.Left VelX
• VelY VelY 10
• If Shape1.Top gt Ht Then
• Shape1.Top 2 Ht - Shape1.Top
• VelY -VelY 0.9
• End If
• If Shape1.Left gt Wd Then
• Shape1.Left 2 Wd - Shape1.Left
• VelX -VelX
• ElseIf Shape1.Left lt 0 Then
• Shape1.Left -Shape1.Left
• VelX -VelX
• End If
• End Sub