Mouse Events. Mouse Driven Events Unlike control_click() which is passed no arguments (unless it's an index for an array), MouseDown, MouseUp and MouseMove.

Mouse Events

Mouse Driven Events

• Unlike control_click() which is passed no arguments (unless it's an index for an array), MouseDown, MouseUp and MouseMove events have much more information available– Button as integer - which mouse button(s) were pressed

– Shift as integer - which modifier keys were pressed

– X and Y as single - the location of the mouse pointer in the coordinate system of the object receiving the mouse event

Mouse Driven Events (2)

• Button– Status of the mouse buttons

• 1 - Left Button

• 2 - Right Button

• 4 - Middle Button

– Multiple buttons are treated as multiple events for MouseUp and MouseDown

Mouse Driven Events (3)

• Shift– Keys (Shift, Control and Alt)

• 1 - Shift Key

• 2 - CTRL Key

• 4 - ALT Key

– Any or all of the modifier keys can be set

Mouse Driven Events (4)

• For the Button or Shift arguments, bitwise logical testing must be performed to determine state. Examples– (shift AND 3) = 3 tests for Shift and CTRL

keys pressed– (Button AND 2) = 2 tests Right button only– (Button AND 3) = 2 tests for Right button only

Mouse Positioning Example #1 • Create a form with a textbox and code:

Private Sub Form_MouseUp(...)moveit = Falseend sub

Private Sub Form_MouseDown(...)moveit = TrueCall Form_Mousemove(Button, Shift, X, Y)End Sub

Private Sub Form_MouseMove(…)If moveit Then Text1.Move X, YEnd Sub

Mouse Positioning Example #2

• Etch-a-sketchPrivate Sub Form_MouseMove(Button As Integer, Shift As Integer,

X As Single, Y As Single)

Line -(X, Y)

End Sub

Mouse Positioning Example #3• Improved Etch-a-sketch

dim moveit

Private Sub Form_Mousemove(…, X, Y)If moveit Then Line -(X, Y) : rem circle (x,y), 50 End Sub

Private Sub Form_MouseUp(…, X, Y)Form1.CurrentX = X Form1.CurrentY = YCall Form_Mousemove(Button, Shift, X, Y)moveit = Not (moveit)End Sub

Mouse Click, Up, Down

• What occurs in what sequence?– Mouse Down is first– Mouse up is second– mouse click is third– mouse up always follows a double click– mouse move always follows a mouse click

List / Combo Boxes

Three types of list controls

• List controls– Drop-down list– Combo-Box

• The last set is “initialized” with the contents of the appropriate drive directory

• These two must be initialized via code

List Box Control• Allows the user to select from a specified set of options (but he cannot

enter an unlisted value)

• Presented as a single window with the items listed sequentially

• Selections must be initialized via code (often as part of form_load)

• The columns property permits display of multiple columns of data in a snaking fashion (horizontal scroll as well as vertical scroll)

• The multiSelect property allows selecting multiple items which are placed in the list property (an array ) and identified by the selected property (an array)– selected(i) = true indicates that the related element of list(i) has been

selected

AddItem Method

• Used to add items to a list box

• Syntax– control.AddItem item– item is the expression you want displayed, and

it can be either numeric or string– if item is a literal string constant, then it must

be enclosed in quotation marks

Arrangement of List Box Items

• By use, with the most used entries appearing first in the list

• Sorted in ascending order either alphabetically, numerically, or chronologically

Sorted Property

• Can be set to either the Boolean value True or the Boolean value False

• If set the True, the list box items will be sorted in ascending order

• If set to False, the list box items will appear in the order in which they were entered

ListIndex Property

• You can use the ListIndex property to refer to an item in the list box

• The first item in a list box has a ListIndex value of 0

• If no items are selected in the list box, the ListIndex property has a value of -1

Default Item• It is customary to select a default item in a

single-selection list box when the interface first appears– the default item should be either the most used

selection or the first selection in the list– lstName.ListIndex = 0 will select the first item

in the lstName list box

• A default selection typically is not made in a multi-selection list box

List Box Initialization Example

Dim I, start_pos, stop_pos, months, thismonth

thismonth = month(Now) ' note: month returns 1-12

months = "January February March April May June "

months = months & "July August September October November December "

start_pos = 1

For item_number = 0 To 11 ' item numbers are zero-based

stop_pos = InStr(start_pos, months, " ")

List1.AddItem Trim(Mid(months, start_pos, stop_pos - start_pos)), item_number

start_pos = stop_pos + 1

Next item_number

' note: listindex is 0-based so we have to subtract 1 to get the correct month selected

List1.ListIndex = thismonth - 1

Combo Box Control (three styles)

• Drop Down (Style 0)– Like a one-line text box with a list attached– User can select a value or enter one of his own– Options are not shown unless user displays them

• Simple Combo Box (Style 1)– Always shows the list of options to the user if you design the box

large enough– User can select a value or enter one of his own

• Drop Down List Box (Style 2)– List is not displayed until user clicks down arrow– User can only select from list of options– Typing in the text box scrolls to best fit option

Lists & Combo Boxes

• The Integralheight property – if true will force box size to display an integral number of lines

and no partial lines– if false will retain box design dimensions, but may display partial

lines

• The listindex property contains the index (0-based) of the selected item (-1 = no item selected)

• The additem method (not event) is used to add or replace an item

• The removeitem method is used to remove an item• The clear method will remove all items

Lists & Combo Boxes (2)

• The sorted property sorts the list but can be very slow when adding to large lists

• The text property contains the last selected item

• The listcount property contains the number of items, always one more than the maximum listindex

• The topindex property contains the index value for the top of the displayed portion of the list when there is a vertical scroll bar

• There are other methods available (Use Object Browser to see them)

List & Combo Box Differences

• Selected and List properties– only for List Boxes which allow multiple selections

• Change event– only for combo boxes and only when a new entry is typed in

• Dropdown event– only for dropdown combo and dropdown list

Variable Arrays

Variable Arrays• A group of variables that have the same name and

data type and are related in some way• Can have as many as 60 dimensions in Visual Basic;

the most commonly used arrays are one-dimensional and two-dimensional

• Programmers use arrays to store related data in the internal memory of the computer

• Data stored inside the computer can be both written and read much faster than data stored in a file on a disk

Variable Arrays

• A one-dimensional array is simply a row (or column) of variables; a two-dimensional array resembles a table in that it has rows and columns

• Each element in an array is identified by a subscript

• You refer to an array element by the array’s name followed by the element’s subscript

Variable Arrays (2)

• Lower-bound is zero by default unless – option base 1 is declared, in which case it is 1– it is explicitly declared using the to keyword

• dim cards(1 to 52)• dim line_numbers(100 to 1000)

• Upper element designated by a long in parentheses after the name - ex. dim cards(51) (an array of 52 items numbered 0-51)

• Arrays must usually be initialized before use using some kind of looping construct or the array statement

dim x(4)x = array(5,7,9,"this",true)

One-dimensional Array

Nebraska New Jersey New Mexico Tennessee Texas

Nebraska

New Jersey

New Mexico

Tennessee

Texas

Two-dimensional Array

Nebraska

New Jersey

New Mexico

Tennessee

Texas

Lincoln

Trenton

Santa Fe

Nashville

Austin

One-dimensional Array

– Dim arrayname(lower subscript To upper subscript) As datatype

– Public arrayname(lower subscript To upper subscript) As datatype

• lower subscript and upper subscript are numbers that define the lowest and the highest subscript in the array

– The Dim (and Public) statements create and initialize the array variables in memory

One-dimensional Array

– Dim strMonthArray(1 To 6) As String– Dim intSquareArray(1 To 5) As Integer– Dim sngNum(1 To 10) As Single– Dim udtEmp(1 To 20) As EmpStruc

– Note: It is not necessary for an array name to contain the word “Array.”

One-dimensional Array

strMonthArray(1) = “Jan”

strMonthArray(2) = “Feb”

strMonthArray(3) = “Mar”

strMonthArray(4) = “Apr”

strMonthArray(5) = “May”

strMonthArray(6) = “June”

One-dimensional Array

For intNum = 1 to 5

intSquareArray(intNum) = intNum * intNum

Next intNum

For intNum = 1 to 10

sngNum(intNum) = Val(InputBox(“Enter number”))

Next intNum

One-dimensional Array

Do While Not EOF(1)

intNum = intNum + 1

Input #1, udtEmp(intNum).Name, udtEmp(intNum).Salary

Loop

Array Initialization• Use loops to initialize

dim row as integer, col as integerstatic big_matrix(1 to 5, 1 to 10) as integerfor row = 1 to 5

for col = 1 to 10big_matrix (row,col) = row*10+col

next colnext row

Calculating the Average

Declare variables

Repeat for intNum = 1 to 20 by 1add array score to intTotal variable

End repeat for intNum

Calculate the average by dividing intTotal by 20

Display the average

Finding the Highest Value

Declare variablesAssign first array value to intHigh variableRepeat for intNum = 2 to 20 by 1

If current array value > intHigh value thenassign current array value to intHigh

End If

End repeat for intNumDisplay the highest value(stored in intHigh)

Updating an ArrayDeclare variablesPrompt user for the value to addRepeat for intNum = 2 to 20 by 1

add value to current array value

End repeat for intNumDisplay “Updated” messageOpen a fileRepeat for intNum = 1 to 20 by 1

Write array value to fileEnd repeat for intNumClose the file

Two-dimensional Array

• Dim arrayname(lower subscript To upper subscript, lower subscript To upper subscript) As datatype

• Public arrayname(lower subscript To upper subscript, lower subscript To upper subscript) As datatype

Two-dimensional Array

– Dim strNameArray(1 To 6, 1 To 3) As String

– Dim intNum(1 To 5, 1 To 10) As Integer– Dim sngSales(1 To 20, 1 To 2) As Single

– Note: It is not necessary for an array name to contain the word “Array.”

Two-dimensional ArrayDeclare variablesOpen the fileRepeat for intRow = 1 to 4 by 1

Repeat for intCol = 1 To 2 by 1Read name from file and store it in the current array element

End repeat for intColEnd repeat for intRowClose the file