ENGG1811 Computing for Engineers Week 9 Dialogues and Forms Numerical Integration

Transcription

1 ENGG1811 Computing for Engineers Week 9 Dialogues and Forms Numerical Integration ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 1

2 References & Info Chapra (Part 2 of ENGG1811 Text) Topic 21 (chapter 15) Custom Dialogue Boxes This week s schedule Tue, Wed am: new material Wed pm: worked example ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 2

3 Forms and Controls VBA has access to the full window library 1. Buttons or similar Controls (window elements) can be placed on sheet. 2. Dialogues are provided for standard interaction such as opening files, choosing colours. Can be called from VBA. 3. Forms (windows with controls placed by the designer) can be embedded in document. Each active element can trigger actions through VBA event procedures ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 3

4 1. Command Buttons Simplest scheme: command buttons Show control tool box Developer tab Insert 2003: View Toolbars Control Toolbox Select command button from bottom group (ActiveX Controls, arrowed) Click and drag on sheet Right-click*, select Properties Change name (cmddemo), caption, font, other properties Right-click again, select View Code VBE allows changes to properties and event handler: cmddemo_click( ) Exit design mode, button becomes active * or pick from Controls on the ribbon Exit Design Mode Command Button ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 4

5 Example: Colour Swatch Lay out a new sheet with named ranges ColourRegion (4 cells) and IndexBox (1 cell) Show the control box, add a button called cmdchangecolour labelled Next Colour Name box ColourRegion IndexBox ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 5

6 Colour Swatch Event Procedure In Design Mode, double click button. Opens up VBA associated with this worksheet, including events for the command button. Sheet needs one variable, changed by the event procedure: Const NUM_COLOURS = 56 ' Excel VBA standard (2003+ compatible) Dim collast As Integer ' last colour index shown (or 0) Private Sub cmdchangecolour_click() collast = 1 + collast Mod NUM_COLOURS With ActiveSheet.Range("ColourRegion").Interior.ColorIndex = collast.range("indexbox").value = collast End With End Sub ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 6

7 Colour Swatch Demo See sheet ColourSwatch on the week 9 Lecture demo spreadsheet. This example is simple enough for all VBA code to be included with the sheet itself Often cmdbuttonxyz_click() just calls a subprogram in a module. ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 7

8 Properties Window Edit characteristics of any static object View by name or grouped by category Accessible from VBE or from control via Properties on shortcut menu or ribbon Units are points (1/72 inch, approx 28 pts per cm), 1 decimal place ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 8

9 2. Built-in Dialogues You ve seen MsgBox before, now use its value: reply = MsgBox("Root found, look for more?", _ vbyesno, "Newton") If reply = vbyes Then MsgBox "Out of jelly beans!", vbcritical ' OK only Select Case MsgBox("I'm feeling tired, can I quit?", _ vbabortretryignore, "Ennui") Case vbabort: Application.Exit Case vbignore: ' do nothing (keep going) Case vbretry: ' keep going anyway End Select Type msgbox to VBA Help for codes ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 9

10 Input box To issue a prompt and obtain a single string from the user you can use the InputBox function Dim strname As String strname = InputBox("What is Your name?") If strname = "" Then Else End If MsgBox "Silent type, eh?" MsgBox "Hello, " & strname Occasionally useful, but large data sets should be on the active sheet, and smaller sets could have customised forms (soon) ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 10

11 Other Builtin Dialogues Getting the user to select a file name is a common requirement: GetOpenFileName("Text Files (*.txt), *.txt") We would use this if we covered reading and writing to text files in ENGG1811 (but we don t) ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 11

12 3. User Forms A user form is an independent window containing controls placed by the designer In the VBE, select Insert - UserForm Resize. From the toolbox, select and place controls. Each is given a default name. For our first example, add three labels, a text box and a command button ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 12

13 Toolbox Controls Control Pfx Tool Graphic Main Properties* Text box txt Value Label lbl Caption Command button cmd Caption List box lst Value, ControlSource Combo box cbo Value, ControlSource Option button opt Value (Boolean) Check box chk Value Spin button spn Value, Min, Max Image img Picture *All have Name, Width, Height, Left, Top, Visible, TabIndex etc ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 13

14 Control Properties Identity Content Can change most attributes of each control (select with circled dropdown) in the Properties window. Important ones arrowed. See also Categorized view. Text attributes Position Behaviour ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 14

15 Initiating Action After designing the form, what then? All controls detect and manage events such as frmgame_activate() rdogender_change() cmdguess_click() cmbaction_change() txtinput_afterupdate() Private Sub lbl1_mousemove(byval Button As Integer, _ ByVal Shift As Integer, ByVal X As Single) Each control s properties are exposed through the object model, so VBA can use and modify them (especially displayed values) Must consider what should happen for each relevant event: event-driven programming Within event handlers normal algorithms apply ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 15

16 An Example Let s continue with the form we re building, it s for an implementation of the children s High- Low guessing game program picks a number between 1 and n (say 100) user guesses, is told high/low/correct user wins if guessed within limited number of tries Can you identify the optimal strategy for the user (it s certainly not random guessing!)? ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 16

17 High-Low Form Rename and reposition elements, add captions in 10pt font, adjust widths: Added sample text in 14pt to confirm suitability of size. lblresult is blank, content will be assigned by VBA ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 17

18 Events What (meaningful) events can occur? 1. Form is activated 2. Form is closed (via the window bar) 3. Reset button is pressed 4. User enters text 1 and 3 are the same; 2 isn t handled Hence only two need to be managed. Event procedures: cmdreset_click() txtguess_afterupdate() why not txtguess_change()? UserForm_Activate() calls cmdreset_click ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 18

19 Document Structure Designs and VBA code are stored in three places in the document: Worksheet has VBA code to initiate form frmhilo has form layout, plus VBA code to handle all events Module1 (rename it HiLo_module) has state variables and all algorithm processing code ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 19

20 Startup We want the form to appear when the sheet is selected (activated) Use the worksheet activation event to position the form and activate it (Show method): ' Display the HiLo form, offset into Excel's window Private Sub Worksheet_Activate() frmhilo.left = Application.Top frmhilo.top = Application.Left frmhilo.show End Sub ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 20

21 Pseudocode for Reset: Event Responses think of a number set guess count to 0 clear lblresult.caption and txtguess.value Pseudocode for User entry: fetch typed string (from txtguess.value) if not a sensible guess then issue error message (assign to lblresult.caption) elseif correctly guessed then issue win message elseif guess limit reached then issue loss message else increment guess count issue keep-trying message dubious logic, allowing the software to be fooled much as viruses exploit logical errors in production software, such as passing a 100,000-character URL to a program that assumes nobody would ever do that! ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 21

22 State Variables State is maintained in the visible elements and in two variables: target number number of guesses These variables and additional procedures are stored in a new module (HiLo_module) Event procedures should contain minimal code: they call procedures in HiLo_module to update state Must use fully qualified names: HiLo_module.PickRandomTarget HiLo_module.ResetGuessCount HiLo_module.Guess(strGuess) ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 22

23 Observation Most of program consists of validating what the user typed Exercise: add a checkbox labelled Show limits If checked (chkshowlimits.checked), display the current range of possible values based on what the player has guessed makes the game easier, especially if there were to be a time limit on each guess adds two controls (labels for the limits) and more VBA in return for richer functionality even fancier: two rectangular frames, one filled to show progress ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 23

24 Debugging Aim is to produce VBA procedures that perform exactly as intended Errors can be introduced at any stage design (poor understanding of problem) pseudocode (poor understanding of solution) implementation (poor understanding of VBA, or typos) VB Editor picks up gross typo-type errors only On execution, could get run-time error such as divide by zero run-time error such as invalid object method normal termination and correct result normal termination and incorrect result Different tests may produce different outcomes ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 24

25 Debugging VB interpreter has full control over the execution of your program If we get a run-time error, VBE shows current execution position Can view simple variable values to help infer error If result is wrong, it may be possible to work out the error, but often you need to know things like: What was the value of this variable at this point in the execution? How many times did this loop execute? When was this variable changed? Did this part of the procedure get executed? VBE can help you get answers to these questions ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 25

26 Error Handling Programs can have errors of several kinds 1. Syntax and semantic errors due to typos or poor understanding of the language 2. Logical errors that produce a different outcome from the expected one 3. Run-time errors The VB Editor can catch most of (1), and the programmer will use various techniques including debugging to deal with (2) (3) normally stops the interpreter ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 26

27 Types of Run-time Error a) Impossible calculations such as divide by zero b) Exceeding data limits (integer overflow etc) c) Array usage errors (index out of bounds) d) Improper object usage (misspelled method or property, semantic error) e) Missing or malformed data (no collection membership test, so this can happen easily) (a) and (c) indicate logical errors or insufficient data validation (b) may be a logical error, or wrong type used (d) is a semantic error (e) is a condition that can be detected and managed ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 27

28 Trapping Errors (Advanced topic) On Error statement controls error handling On Error GoTo label On Error GoTo 0 On Error Resume Next If an error occurs, transfer control to the labelled statement Restore default handler (terminate execution on error) Ignore error and continue with statement following the error Error handlers are labelled statements local to a subprogram, often at the end, and preceded by Exit Sub statements ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 28

29 Worked Example: Numeric Integration Numerical integration approximates the solution to a definite integral that may not have a closed form by using a series of shapes to model the area under the curve Simplest of these is the Trapezoidal Rule, which uses thin vertical slices with a straight line at the top (forming adjacent trapeziums) a f (x) b Integral of f (x) from a to b is approximated by the sum of the areas inside the red trapeziums ENGG1811 UNSW, CRICOS Provider No: 00098G W10 slide 31

30 Trapezoidal Rule, theory References: Wikipedia, many other web refs Animation: zoidal/trapezoidalaa.html After doing the maths for n equally spaced panels, the formula reduces to b a f ( x) dx f ( x ) 2 f ( x1 ) 2 f ( x2) 2 f ( xn 1) 2 f ( x 0 n ) Panel width b a n Twice the middle values where xi a i( b a) / n a i* End-points counted once only ENGG1811 UNSW, CRICOS Provider No: 00098G W10 slide 32

31 Trapezoidal Rule, pseudocode We can easily convert this to pseudocode: set sum to f (a) + f (b) set delta to the panel width For p = To add to sum Next p area = ENGG1811 UNSW, CRICOS Provider No: 00098G W10 slide 33

32 Trapezoidal Rule, implementation Function TrapArea(a As Double, b As Double, _ n As Integer) As Double Limitations: for this quick example, we will represent the function to be integrated as a VBA function called directly from TrapArea. It is possible to specify it as a formula on the sheet, which is easier for end users ENGG1811 UNSW, CRICOS Provider No: 00098G W10 slide 34

33 Summary Controls can be placed directly on the sheet to add interactivity between sheet and VBA Built-in dialogues are powerful but not universally available Forms provide more control over user interface Form programming focuses on events Debugging techniques include state display using Debug.Print state inspection after error or breakpoint single stepping, watch expressions careful code reviews Error handling regains control after unexpected program state transitions ENGG1811 UNSW, CRICOS Provider No: 00098G W9 slide 35