![Calling Event Procedures
Calling an event procedure allows reuse of code
[Call] ProcedureName (arguments)
Keyword Call is optional and rarely used
Examples
Call clearButton_Click (sender, e)
--OR--
clearButton_Click (sender, e)](https://image.slidesharecdn.com/cis160finalreview-120822102042-phpapp02/85/CIS160-final-review-18-320.jpg)
CIS160 final review
- 2. Final Exam 100 points Open book, open notes True/false, multiple choice, fill-in, short answer
- 3. Variables and Constants Variable: Memory locations that hold data that can be changed during project execution Example: customer’s name Named Constant: Memory locations that hold data that cannot be changed during project execution Example: sales tax rate
- 4. Using Variables and Constants In Visual Basic when you declare a Variable or Named Constant An area of memory is reserved A name is assigned called an Identifier
- 5. Declaration Statements Assign name and data type Not executable statements unless a value is assigned on same line
- 6. Naming Variables & Constants Must follow Visual Basic Naming Rules Cannot use reserved words or keywords that Basic has assigned a meaning such as print, name, and value Must begin with a letter and no spaces or periods Should follow Naming Conventions Names should be meaningful Include class (data type) of variable in name Use mixed case for variables and uppercase for constants
- 7. Scope and Lifetime of Variables Visibility of a variable is its scope Where is that identifier valid? Scope may be Namespace: throughout project Module: within current form/class Local: within a procedure Block: within a portion of a procedure Lifetime of a variable is the period of time the variable exists
- 8. Static Variables Use static to declare local and block level variables that need to retain their value Variable will not be initialized next time procedure runs, and will have last value assigned If the variable is used in multiple procedures, declare it at the module level with private Pass data as arguments if one procedure calls the other
- 9. Converting Strings to Numeric Values Use Parse methods to convert a string to its numeric value before it’s used in a calculation Each numeric data type class has a Parse method Parse method returns a value that can be used in calculations Parse method fails if user enters nonnumeric data, leaves data blank, or entry exceeds data type size
- 10. Try/Catch Blocks Enclose statements that might cause a run-time error within Try/Catch block If an exception occurs while statements in the Try block are executing, code execution is moved to the Catch Block If a Finally statement is included, the code in that section executes last, whether or not an exception occurred
- 11. Using Overloaded Methods This OOP feature allows the Messagebox Show method to act differently for different arguments Each argument list is called a signature: the Show method has multiple signatures Supplied arguments must exactly match one of the signatures provided by the method
- 12. If Statements Used to make decisions If true, only the Then clause is executed; if false, only Else clause is executed (if there is an Else) Block If…Then…Else must always conclude with End If Then must be on same line as If or ElseIf End If and Else appear alone on a line
- 13. Conditions Test in an If statement is typically based on a condition Six relational operators are used for comparison of numbers, dates, and text Equal sign is used to test for equality Strings are compared using ANSI value of each character CIS is less than CNA MATH is less than MATH&
- 14. Combining Logical Operators Compound conditions can combine multiple logical conditions And describes conditions where both tests are true Or describes conditions where either or both tests are true When both And and Or are evaluated And is evaluated before the Or Use parenthesis to change the order of evaluation
- 15. Input Validation Check to see if valid values were entered or available Can check for a range of values (often called “reasonableness”) If Integer.Parse(scoreTextBox.Text) >= 0 Then ‘ Code to perform calculations…. Check for a required field (not blank) If studentIDTextBox.Text <> "" Then ...
- 16. Select Case Use Select Case to test one value for different matches (“cases”) Usually simpler and clearer than nested If No limit to number of statements that follow a Case statement When using a relational operator must use the word Is Use the word “To” to indicate a range with two endpoints
- 17. Sharing an Event Procedure Add object/event combinations to the Handles clause at the top of an event procedure Allows the procedure to be associated with different events or other controls Sender argument identifies which object had the event happen Cast (convert) sender to a specific object type using the CType function
- 18. Calling Event Procedures Calling an event procedure allows reuse of code [Call] ProcedureName (arguments) Keyword Call is optional and rarely used Examples Call clearButton_Click (sender, e) --OR-- clearButton_Click (sender, e)
- 19. Breakpoints Breakpoints allow you to follow the execution of your code while program is running Can hover the cursor over a variable or property to see the current value in the current procedure Can execute each line, skip procedures Can use Console.Writeline to output values to track code execution Variables and property values can be seen in different windows (autos, locals) while code is executing
- 20. Writing Procedures A general procedure is reusable code which can be called from multiple procedures Useful for breaking down large sections of code into smaller units Two types: Sub Procedure performs actions Function Procedure performs actions AND returns a value (the return value)
- 21. Passing Arguments to Procedures If a procedure includes an argument, any call to the procedure must supply a value for the argument Number of arguments, sequence and data type must match Arguments are passed one of two ways: ByVal – Sends a copy of the argument’s value, original cannot be altered ByRef - Sends a reference to the memory location where the original is stored and the procedure may change the argument’s original value If not specified, arguments are passed by value
- 22. Modal versus Modeless Forms Show method displays a form as modeless - means that both forms are open and the user can move from one form to the other ShowDialog method displays a new form as modal - the user must close the form in order to return to the original form No other program code in the original form can execute until the user responds to and hides or closes the modal form
- 23. ListBoxes and ComboBoxes Provide the user with a list of choices to select from Various styles of display, choose based on Space available Need to select from an existing list Need to add to a list Listboxes and comboboxes share most of the same properties and operate in a similar way Combo box control has a DropDown Style property Combo box allows text entry
- 24. The Items Collection List of items in a ListBox or ComboBox is a collection Collection is group of like objects Items referenced by number (zero-based) Collections are objects that have properties and methods that allow Adding items Removing items Referring to an individual element/member Counting items
- 25. SelectedIndex Index number of currently selected item is stored in the SelectedIndex property Property is zero-based If no list item is selected, SelectedIndex property is negative 1 (-1) Use to select an item in list or deselect all items
- 26. Do Loops A loop repeats a series of instructions An iteration is a single execution of the statement(s) in the loop Used when the exact number of iterations is unknown A Do/Loop terminates based on condition change Execution of the loop continues while a condition is True or until a condition is True The condition can be placed at the top or the bottom of the loop
- 27. Pretest vs. Posttest Pretest: test before enter loop loop may never be executed since test executes BEFORE entering loop Do While … Loop Do Until … Loop Posttest: test at end of loop loop will always be executed at least once Do … Loop While Do … Loop Until
- 28. For/Next Loops Used to repeat statements in a loop a specific number of times Uses a numeric counter variable called Counter or Loop Index Counter is incremented at the bottom of the loop on each iteration Start value sets initial value for counter End value sets final value for counter Step value can be included to specify the incrementing amount Step can be a negative number
- 29. For/Each Loops Used to repeat statements for each member of a group A reference variable is used to “point” to each item Must be the data type of each item in group
- 30. Exiting Loops In some situations you may need to exit the loop early Use the Exit For or Exit Do statement inside the loop Typically used in an If statement (some condition determines whether to exit the loop or not)
- 31. Arrays List or series of variables all referenced by the same name Similar to list of values for list boxes and combo boxes, without the box Each variable is distinguished by an index Each variable is the same data type Individual elements are treated the same as any other individual variable
- 32. Array Terms Element: Individual item in the array Subscript (or index): Zero-based identifier used to reference the specific elements in the array Must be an integer Subscript Boundaries Lower Subscript, 0 by default Upper Subscript
- 33. Subscripts Subscripts may be constants, variables, or numeric expressions Subscripts must be integers Subscripts begin at zero (0) VB throws exceptions for subscripts that are out of range (upper and lower bounds).