DragDrop Technique

MouseDown

SourceControl.Drag in MouseDowm event

DragIcon of the SourceControl you'are dragging. Pick DragIcon from available Graphics\Icons\DragDrop subdirectory

DragOver ' Use this event to give some feedback to user. Eg: change colour of control when something is dragged over it.

DragDrop ' Refer to SourceControl to know which control has just been dropped. Can use property Tag of SourceControl to know more about it. Use TypeOf function to know what type of SourceControl it was.

 

VB Programming Syntax

Naming Convention: txtTextBox, lblLabel, CmdCommandButton, etcẨ

Comment character is '

Variable Declaration: You don't have to declare that you are about to use a new variable or the data type of that variable.

Option Explicit ' Always use this statement in the General Declaration section to indicate that any variables used must be declared first with a Dim or Global statement. Note that variables are initialised to 0 for number and Null string for string.

Program Statement can be single statement or Block of statements.

What is a Block of statements?

Assignment concept:

The statement

Counter = Counter + 1

means getting the Counter value from its storage, adding 1 to this value,

then put it back to Counter storage. The = sign does not mean EQUAL

Arithmetic Expression

Like algebra, Multiplication and Division take precedence over Addition and Substraction. If in doubt, use single brackets.

Arithmetic Operators: +, -, *, / , Mod, \

Logical Expression is used in If ..Then..Else.. End If statements. The result is True or False, and cannot be used for arithmetic calculation.

NOT, AND take precedence over OR. If not sure use single brackets. Eg:

If ItsHot OR theSunShines AND IamFree Then

    IgotoTheBeach

End If

Is the same as

 

If ItsHot OR (theSunShines AND IamFree) Then

    IgotoTheBeach

End If

Logical operators: >, < ,=, <=, >= , <>, NOT

 

Data Types

 

Integer ' -32,768 to 32,767; fractions are rounded.

Single ' floating point number stored in 4 bytes

Boolean ' Store True or False

String ' Such as "Hello, world!"

A character is a string of one character.

Variant ' General purpose data type

Date ' Store Date

Array of Variables

Array of Controls, Index

 

Scope (or Visibility) of Variables

 

Global ' Declare Globally in Module

Dim ' Declare locally, with or without data type

Public ' let people access

Private ' only use inside this Form/Module

Static ' Variable value retains even after the Sub/Function had reached the end.

 

In general:

Variables declared within a Sub/Function disappears once the execution reaches the end.

No Sub/Function can access variables declared locally inside another Sub/Function

Anything from one Form cannot access variables in another Form.

All Subs, Functions of a Form/Module can access its General Declaration Section

All Subs, Functions of a Project can access everything declared Public and Global in the Modules

 

Sub and Function

 

Parameters act as place holder. They can have different names from variables passed to the Sub/Function.

Parameters may be damaged by Sub/Function process. To avoid damage use ByVal

The following example uses the Sub statement to define the name, arguments, and code that form the body of a Sub procedure.

' Sub procedure with two arguments.

 

Sub ComputeArea (Length, TheWidth)

Dim Area As Single ' Declare local variable.

 

If (Length = 0) Or (TheWidth = 0) Then

 

' If either argument = 0.

 

Exit Sub ' Exit Sub immediately.

End If

Area = Length * TheWidth ' Calculate area of rectangle.

Debug.Print Area ' Print Area to Debug window.

End Sub

Function Returns a Value in the declared Data Type.

Eg: Function IsDate (MyDate.text) returns a Boolean value (ie. True/False) after checking if MyDate.Text is a valid date.

Function UCase(myString) returns a String which is myString converted to Uppercase.

Side Effects means Paramaters passed to Function being damaged by the Function process without user's knowledge.

This example uses the Function statement to declare the name, arguments, and code that form the body of a Function procedure.

 

The following user-defined function returns the square root of the argument passed to it.

Function CalculateSquareRoot(NumberArg As Single) As Single

If NumberArg < 0 Then ' Evaluate argument.

CalculateSquareRoot = 0

Else

CalculateSquareRoot = Sqr(NumberArg) ' Return square root.

End If

End Function

Some Event Subs are treated just like normal Sub.

 

Input/Output text string from/to a text file

Open "todo.txt" for Input as #1 ' Open the Text file for Input

Do While Not EOF(1) ' Keep reading 1 line at a time until reaching the end

Line Input #1, Aline

List1.AddItem Aline ' Add the line of text to Listbox List1

Loop

Close #1 ' Close the file

Open "todo.txt" for Output as #2 ' Open the Text file for output

' Output content of Listbox List1 to "todo.txt"

For i = 0 to List1.Listcount-1 ' Go thru from 1^st to last line in List1

Print #2, Aline ' Write the line of text to file

Next i

Close #2 ' Close the file

The App object

 

App.Path ' Return the Folder where Application file (ie. .exe ) resides

It may not be terminated with "\" so to make sure append the character "\" on the right if the last character is not "\":

LocalDir = App.Path

If Right(LocalDir,1) <> "\" then

LocalDir = LocalDir & "\"

End if

 

App.PrevInstance ' Use this to check if the program has already been loaded. ie. We don't want user to load several copy of the programs.

If App.PrevInstance = True then

MsgBox "This program is active, please restore its window and use."

End ‘ Terminate the program

End if

 

 

Use the menu command Project | Properties (click Tab MAKE) to enter the Major and Minor Version number of your application and to select the icon of which form as the icon of the application.

 

Data type functions

 

IsNumeric checks if the string represents a number

IsDate checks if the string represents a valid Date

Example:

If IsDate(theDate.text) Then

TheDate.text = Format(theDate.text, "dd/mm/yyyy")

End if

Val , CSng convert a string to a number.

Str converts a number to a string, watch that it gives you a blank space on the left of the number string

 

Sendkeys Function

 

Sendkeys "Very Good" ' Emulate entering the "Very Good" keystrokes

Sendkeys "{TAB}" ' Emulate tapping the TAB key

"+bc" ' SHIFT "bc", hold down the Shift key while pressing b and c

"^m" ' CTRL m, hold down the Ctrl key while pressing m

"%h" ' ALT h, hold down the Alt key while pressing h

 

Control Flow

 

Flow of execution of code may be changed with Control Flow facilities

Selection with If and Case statements

 

If WeeklyIncome < 100 then

Tax = 0.0

End If

If OutsideTemparature >= 35 then
GotoTheBeach
Else
GotoTheMovies
End If

If Age > 60 then
Category = Pensioner
ElseIf Age < 18 then
Category = Child
Else
Category= Adult
End if

Select Case GivenNumber ' Evaluate GivenNumber.

Case 1 To 5 ' Number between 1 and 5.

Debug.Print "Between 1 and 5"

' The following is the only Case clause that evaluates to True.

Case 6, 7, 8 ' Number between 6 and 8.

Debug.Print "Between 6 and 8"

Case Is > 8 And GivenNumber < 11 ' Number is 9 or 10.

Debug.Print "Greater than 8"

Case Else ' Other values.

Debug.Print "Not between 1 and 10"

End Select

 

Iteration with For and Do statements with For and Do statements

Use For..Next when there is a fixed number of iterations

The following example uses the For...Next statement to create a string that contains 10 instances of the numbers 0 through 9, each string separated from the other by a single space. The outer loop uses a loop counter variable that is decremented each time through the loop.

Dim i, Chars, MyString

MyString=""

For i = 10 To 1 Step -1      ' Set up 10 repetitions.

For Chars = 0 To 9     ' Set up 10 repetitions.

MyString = MyString & Chars     ' Append number to string.
Next Chars ' Increment counter

MyString = MyString & " "      ' Append a space.

Next i

Use Do.. Loop when you are not sure of the exact number of iterations.

The following example shows how Do...Loop statements can be used. The inner Do...Loop statement loops 10 times, sets the value of the flag to False, and exits prematurely using the Exit Do statement. The outer loop exits immediately upon checking the value of the flag.

 

Dim Check, Counter

Check = True: Counter = 0 ' Initialize variables.

Do ' Outer loop.

Do While Counter < 20 ' Inner loop.

Counter = Counter + 1 ' Increment Counter.

If Counter = 10 Then ' If condition is True.

Check = False ' Set value of flag to False.

Exit Do ' Exit inner loop.

End If

Loop

Loop Until Check = False ' Exit outer loop immediately.

 

Note that a

Do While (Logical Expression)Ẩ

Ẩ..

Loop

may not go through the loop at all if the condition is not satisfied at the beginning.

Whereas

Do

Ẩ.

Loop Until (Logical Expression)

will go thru the loop at least once, because the Logical Expression is not calculated until the end of the loop.

When you use a Do Loop remember to initialise some data value, such as i.

Goto Label ' Label must be terminated with a colon eg: DoAgain:

 

String manipulation

 

MyString = "" ' assign a null string to MyString, ie. Clear the string

String concatenation symbol &

Example: ResultString = "Hello, " & "World! " & " How are you?"

ResultString = Left (GivenString, 4) ' Extract leftmost 4 characters

ResultString = Right(GivenString, 6) ' Extract rightmost 4 characters

ResultString = Mid(GivenString, 5,8) ' Extract rightmost 8 characters, starting from column 5

ResultString = Mid(GivenString, 12) ' Extract the remaining of the string starting from Column 12

ResultString = Space(40) ' Return 40 blank spaces

Pos= InStr(GivenString,"Hello") ' Return column where substring "Hello" is found.

GivenString = Trim(GivenString) ' Remove both leading and trailing blank spaces

ResultString = Ucase(GivenString) ' Convert all characters in given string to Uppercase

Example: Obtain Firstname, Middlename and Surname from the full name

 

Date manipulation

• Now ' Return current Date and Time

• TheShortDate = Format (Now, "dd/mm/yy")

• Be wary of Year2000 compliance

• DateDiff ("d", Now, AfutureDate)

• TwoHourLater = DateAdd("h",2, Now )

• MyDate = #February 12, 1969# ' Assign a date.

• MyWeekDay = Weekday(MyDate) ' MyWeekDay contains 4 because

• ' MyDate represents a Wednesday.

Example: Obtain current Date in format like "Saturday, 21 February 1998"

 

Debugging facilities

• Place the cursor on top of a variable to see its value.

• Toggle BreakPoint with F9 or by clicking on the left margin of source code.

• Single Step with F8

• Step Over a Sub/Function with Shift+F8

• Drag Round dot on the left margin to required Next Statement

• Start/Continue with F5

Add Watch

When value changes

When value is TRUE, where value can be an expression.

 

Immediate Window

Use Print statement to examine data. Press enter on any statement to execute it.

Can insert temporary statement to change value of variables

Terminate the program by using the Menu command Run | End or by clicking the square symbol.