VB – Event driven Programming Timers & Motion, Sub & Function Arif Zaman

Form Properties Caption, Font Name (don’t 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)

Graphics AutoRedraw=TRUE (if graphics) DrawWidth DrawMode (read on your own) DrawStyle FillColor FillStyle

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.

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

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.

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.

This works Private Sub Form_Click() Form1.Left = Form1.Left + 50 End Sub Because Form.Left is global

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.

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

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)

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 Command1.Left = i/100 Next i End Sub

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

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 PosX>Height Then VelY = -VelY PosX = 2*Height – PosX End If

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 > Ht Then Shape1.Top = 2 * Ht - Shape1.Top VelY = -VelY * 0.9 End If If Shape1.Left > Wd Then Shape1.Left = 2 * Wd - Shape1.Left VelX = -VelX ElseIf Shape1.Left < 0 Then Shape1.Left = -Shape1.Left VelX = -VelX End If End Sub