Chapter 7. Lists, Loops, and Printing The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill

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1 Chapter 7 Lists, Loops, and Printing McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved.

2 Chapter Objectives - 1 Create and use list boxes and combo boxes Differentiate among the available types of combo boxes Enter items into list boxes using the Items collection in the Properties window Add and remove items in a list at run time Determine which item in a list is selected McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-2

3 Chapter Objectives - 2 Use the Items.Count property to determine the number of items in a list Display a selected item from a list Use do, while, and for loops to execute a series of statements Skip to the next iteration of a loop by using the continue statement Send information to the printer or the Print Preview window using the PrintDocument class McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-3

4 List Boxes and Combo Boxes - 1 List boxes and combo boxes Have most of the same properties and operate in a similar fashion One exception is that a combo box control has a DropDownStyle property Determines whether list box has a text box for user entry and if the list will drop down Provide the user with a list of items from which to select McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-4

5 List Boxes and Combo Boxes - 2 Various styles, choose according to space available and how the box operates Simple list box or drop-down list ComboBox DropDownStyle = DropDownList Type a new entry to the list Drop-down combo box DropDownStyle = Drop-Down Simple combo box DropDownStyle = Simple Combo boxes have a Text property Set or remove at design time List boxes have a Text property Access it only at run time McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-5

6 List Boxes and Combo Boxes - 3 McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-6

7 The Items Collection - 1 The list of items in a list box or combo box Collections are objects that have properties and methods that allow Adding items Removing items Referring to individual elements Counting items Clearing the collection McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-7

8 The Items Collection - 2 Can refer to the individual items in a collection by an index Zero based For a collection of ten items, the indexes range from 0 to 9 To refer to the first item in the Items collection use Items[0] Notice the square brackets McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-8

9 Filling a List Several methods to fill the Items collection of a list box or combo box Fill the list at design time if the list is known and the list never changes Define the Items collection in the Properties window Fill the list during program execution Items.Add or Items.Insert methods McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-9

10 Using the Properties Window - 1 Define the Items collection at design time Select the control Scroll the Properties window to the Items property Click the ellipsis button to open the String Collection Editor Type the list items Click OK If needed, open the editor again to modify the list McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-10

11 Using the Properties Window - 2 McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-11

12 Using the Items.Add Method Items that can be added to a list at run time include: Variables, constants, contents of the text box at the top of a combo box, or the text property of another control Alter placement of a new item by setting the control s Sorted property to true McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-12

13 General Form The Items.Add Method Object.Items.Add(ItemValue); Examples schoolslistbox.items.add("harvard"); schoolslistbox.items.add("stanford"); schoolslistbox.items.add(schoolstextbox.text); majorscombobox.items.add(majorscombobox.text); majorscombobox.items.add(majorstring); Use the Items.Add method to add a value entered in the text box portion of a combo box (not automatically added) coffeecombobox.items.add(coffeecombobox.text); Add contents of a text box to a list box schoolslistbox.items.add(schooltextbox.text); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-13

14 Using the Items.Insert Method Choose location for new item added to list Items.Insert method Specify index position for new item An existing position or end of list Index position is zero based First position, use index position = 0 Inserting an item beyond end of list throws an exception Do not set list control s Sorted property to true McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-14

15 The Items.Insert Method General Form Object.Items.Insert(IndexPosition, ItemValue); Examples schoolslistbox.items.insert(0, "Harvard"); majorscombobox.items.insert(1, majorscombobox.text); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-15

16 The SelectedIndex Property Index number of the currently selected item is stored in the SelectedIndex property If no list item is selected, the SelectedIndex property is negative 1 ( 1) Set the SelectedIndex property in code to select an item in the list or deselect all items // Select the fourth item in list. coffeetypeslistbox.selectedindex = 3; // Deselect all items in list. coffeetypeslistbox.selectedindex = -1; McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-16

17 The Items.Count Property Use to determine the number of items in the list totalitemsinteger = itemslistbox.items.count; MessageBox.Show( The number of items in the list is + itemslistbox.items.count.tostring()); Items.Count is always one more than the highest possible SelectedIndex because indexes begin with zero Example: For a list of five items Items.Count = 5 Highest index = 4 Possible values for SelectedIndex = 0, 1, 2, 3, 4 McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-17

18 Referencing the Items Collection - 1 Use the index of the item to reference a specific item in an Items collection Specify which element to select by including an index Use square brackets to reference the index position of a list Index of first list element is zero Highest index is Items.Count - 1 McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-18

19 Referencing the Items Collection - 2 Combine the Items property and the SelectedIndex property to refer to a selected element of a list selectedflavorstring = flavorlistbox.items[flavorlistbox.selectedindex].tostring(); Retrieve the selected list item by referring to the Text property of the control selectedmajorlabel.text = majorscombobox.text; Assigning a value to an item replaces previous contents of that position schoolslistbox.items[0] = My School ; McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-19

20 Removing an Item from a List Items.RemoveAt method Removes an item by index First list element is 0, last element is Items.Count -1 An invalid index will cause an IndexOutOfRange exception nameslistbox.items.removeat[0]; schoolscombobox.items.removeat[indexinteger]; coffeecombobox.items.removeat(coffeecombobox.selectedindex); Items.Remove method Looks for the specified string, removes item if string found No exception is generated if the item is not found nameslistbox.items.remove[ My School ]; schoolscombobox.items.remove(schooltextbox.text); coffeecombobox.items.remove(coffeecombobox.text); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-20

21 Clearing a List Items.Clear method Empty a combo box or list box Clear all items from a list // Confirm clearing the majors list. DialogResult responsedialogresult; responsedialogresult = MessageBox.Show("Clear the majors list?", "Clear Majors List", MessageBoxButtons.YesNo, MessageBoxIcon.Question); if (responsedialogresult == DialogResult.Yes) { majorscombobox.items.clear(); } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-21

22 List Box and Combo Box Events SelectedIndexChanged event Occurs when the user makes a selection from a list TextChanged event Each keystroke generates a TextChanged event Available in combo boxes not list boxes Enter event Occurs when a control receives the focus Use to make existing text appear selected Leave event Fires when a control loses focus Often used for validating input data McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-22

23 The while and do/while Loops - 1 Looping Process of repeating a series of instructions Loop Group of repeated instructions Iteration Single execution of the statement(s) in a loop while or do/while loop Terminates based on a condition specified McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-23

24 The while and do/while Loops - 2 Execution of statements in the loop continue while a condition is true Used when the exact number of iterations needed is not known ahead of time while loop Tests for completion at the top of a loop Also called a pretest or entry test Statements in loop never execute if terminating condition is true first time it is tested When statements inside loop do not execute, control passes to statement following end of loop totalinteger = 0; while (totalinteger!= 0) { // Statements in loop (will never be done). } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-24

25 The while and do/while Loops - 3 do/while loop Tests for completion at bottom of loop Also called a posttest or exit test Statements inside loop will always execute at least once McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-25

26 The bool Data Type Revisited bool variables can be very useful for setting and testing loop conditions bool variables are always in one of two states true or false Often referred to as switches or flags To use a bool variable for loop control Declare the variable and set its initial value When a particular situation occurs, set the variable to true Make the loop condition test for true (continue executing the loop as long as the condition is not true) bool itemfoundboolean = false; while (! itemfoundboolean) // Loop when condition is false (not true). { // Statement(s) in loop. // Must include a statement that sets itemfoundboolean to true. } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-26

27 for Loops - 1 Used to repeat statements in a loop a specific number of times Three parts of a for loop (statement), each separated by a semicolon Initialization More than one initialization action can be used, separate each with commas Condition Action to occur after each iteration More than one action to execute at end of each iteration of the loop can be written Uses a numeric counter variable, the loop index, which is tested to determine the number of times the statements inside the loop will execute McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-27

28 for Loops - 2 Counter-controlled loop normally has three elements Initialize the counter The loop index, a properly initialized numeric variable Test the counter to determine when to terminate the loop Condition tests the value of the loop index variable Increment the counter Add to or subtract from the loop index variable, the loop index is incremented after each iteration All statements between a pair of braces following a for statement are the body of the loop Statements are executed a specified number of times McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-28

29 The for Statement Examples for (int indexinteger = 2; indexinteger <= 100; indexinteger += 2) for (countinteger = startinteger; countinteger < endinteger; countinteger += incrementinteger) for (int countinteger = 0; countinteger <= coffeetypecombobox.items.count 1; countinteger++) for (ratedecimal = 0.05M; ratedecimal < 0.25M; ratedecimal += 0.05M) for (int countdowninteger = 10; countdowninteger > 0; countdowninteger ) Program checks condition after comparison is done If condition is true, loop continues execution If condition is false, loop is exited Control passes to statement following closing brace McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-29

30 Negative Increment or Counting Backward Increment or decrement (reduce by one) the counter variable To decrement a counter variable write the condition to test for the lower bound Loop continues as long as index variable is greater than the test value //Count down. for (int countinteger = 10; countinteger > 0; countinteger--) { //Statements in the body of the loop. } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-30

31 Conditions Satisfied before Entry Final value reached before entry into loop Statements in body of loop never executed // An unexecutable loop. int finalinteger = 5; for (int indexinteger = 6; indexinteger < finalinteger; indexinteger++) { // The execution will never reach here. } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-31

32 Endless Loops Never change the value of the index variable inside the loop Poor programming practice May lead to an endless loop // Poor Programming. For (int indexinteger = 1; indexinteger < 10; indexinteger++) { indexinteger = 1; } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-32

33 Exiting for Loops To exit an endless loop Click on an application's Close box Use the Stop Debugging button in the IDE Place a break statement to exit a for, while or do/while loop Good programming practices dictate exiting loops properly, not with a break McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-33

34 Skipping to the Next Iteration of a Loop Use a continue statement to skip the next iteration of the loop Continue statement transfers control to the end of the loop Retests the loop exit condition // Continue a for loop. for (int loopinteger = 0; loopinteger <= namelistbox.items.count 1; loopinteger++) { if (namelistbox.items[loopinteger].tostring() == string.empty) { continue; } // Code to do something with the name found. Console.WriteLine("Name = " + namelistbox.items[loopinteger].tostring()); } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-34

35 Making Entries Appear Selected Make text in a text box or list appear selected If a text box fails validation, select the text Selecting the entry in a text box When a user tabs into a text box that already has an entry, the user-friendly approach is to select the text Use the SelectAll method Place the SelectAll method in the text box s Enter event handler Occurs when the control receives the focus McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-35

36 Sending Information to the Printer Use the.net PrintDocument and PrintPreviewDialog components from the Printing tab of the toolbox Printing is done through the Windows environment Allows use of fonts installed on any given system Printing dialogs and page setup are the same as any other Microsoft product Several companies sell utilities that do a nice job of designing and printing reports C# Professional Edition and Team System Edition include Crystal Reports for creating reports from database files McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-36

37 The PrintDocument Component Set up output for the printer using methods and events of the PrintDocument component Appears in component tray McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-37

38 The PrintDocument Print Method Print method sends command to print information according to the layout specified in the PrintPage event handler Place Print method in the Click event handler for a button or menu item McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-38

39 Setting Up the Print Output The code to set up the printed page belongs in the PrintDocument's PrintPage event handler The PrintPage event fires once for each page to be printed This technique is referred to as a callback In a callback the object notifies the program it needs to do something by firing an event The PrintDocument Print method executes the PrintPage event handler Holds code that describes exactly how pages should print The PrintDocument object also fires events for BeginPrint and EndPrint Code can be written for these events System.Drawing.Printing.PrintPageEventArgs e argument Properties and methods of PrintPageEventArgs Determines page margins and sends a string of text to the page McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-39

40 The Graphics Page Set up a graphics page in memory Page is sent to the printer Page can contain strings of text and graphic elements Specify the exact X and Y coordinates of each element to be printed on the page The X coordinate is the horizontal distance across the page The Y coordinate is the vertical distance from the top of the page Measurements are in pixels McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-40

41 Using the DrawString Method Used to send a line of text to the graphics page Belongs to the Graphics object of the PrintPageEventArgs argument Is an overloaded method, there are several forms for calling the method Arguments of the DrawString method include What to print What font and color to print in Where to print, using X and Y coordinates Set up the font and coordinates before executing the DrawString method McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-41

42 The DrawString Method General Form (One simple argument list) GraphicsObject.DrawString(StringToPrint, Font, Brush, Xcoordinate, Ycoordinate); Examples e.graphics.drawstring(printlinestring, printfont, Brushes.Black, horizontalprintlocationfloat, verticalprintlocationfloat); e.graphics.drawstring("my text string", myfont, Brushes.Black, 100.0, 100.0); e.graphics.drawstring(nametextbox.text, new Font ("Arial", 10), Brushes.Red, leftmarginfloat, currentlinefloat); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-42

43 Setting the X and Y Coordinates - 1 For each print line, specify X and Y coordinates Create variables declared as float data type to hold the X and Y values The PrintPageEventArgs argument has several useful properties to determine the present settings MarginBounds PageBounds PageSettings Example: Set the X coordinate to the current left margin and the Y coordinate to the top margin horizontalprintlocationfloat = e.marginbounds.left; verticalprintlocationfloat = e.marginbounds.top; McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-43

44 Setting the X and Y Coordinates - 2 To print multiple lines, increment the Y coordinate (forces next line down the page) Add the height of a line to the previous Y coordinate to calculate the next line s Y coordinate Find height of a line in the current font using the font s GetHeight method // Declarations at the top of the method. Font printfont = new Font("Arial", 12); float lineheightfloat = printfont.getheight; float horizontalprintlocationfloat = e.marginbounds.left; float verticalprintlocationfloat = e.marginbounds.top; // Print a line. e.graphics.drawstring(printlinestring, printfont, Brushes.Black, horizontalprintlocationfloat, verticalprintlocationfloat; // Increment the Y position for the next line. verticalprintlocationfloat += lineheightfloat; McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-44

45 Printing Summary Easy steps for nearly all printing tasks Place code in PrintPage event handler of the PrintDocument component 1.At the top of the method, define the font(s), line height, and X and Y coordinates 2.Set up the line to print 3.Print the line 4.Increment the Y coordinate if another line will be printed 5.Place steps 2, 3, and 4 inside a loop if there are multiple lines to print McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-45

46 Printing the Contents of a List Box Combine the techniques for printing, looping, and the list box properties The Items.Count property provides the number of iterations for the loop The Items collection allows the actual values from the list to print // Print out all items in the coffeecombobox list. for (int indexinteger = 0; indexinteger < coffeecombobox.items.count; indexinteger++) { // Set up a line. printlinestring = coffeecombobox.items[indexinteger]; // Send the line to the graphics page object. e.graphics.drawstring(printlinestring, printfont, Brushes.Black, horizontalprintlocationfloat, verticalprintlocationfloat); // Increment the Y position for the next line. verticalprintlocationfloat += lineheightfloat; } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-46

47 Printing the Selected Item from a List Use the Text property to print the selected item from a list box or combo box // Set up the line. printlinestring = Coffee: + coffeecombobox.text + Syrup: + syruplistbox.text; // Send the line to the graphics page object. e.graphics.drawstring(printlinestring, printfont, Brushes.Black, horizontalprintlocationfloat, verticalprintlocationfloat); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-47

48 Aligning Decimal Columns - 1 It is important to align the decimal points of numeric data Proportional fonts make aligning decimal points tricky Format each number to be printed and measure the length of the formatted string Declare an object as a SizeF structure Has a Width property Use the MeasureString method of the Graphics class to determine the width of a formatted string in pixels McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-48

49 Aligning Decimal Columns - 2 // Print aligned columns. Font printfont = new Font("Arial", 12); float lineheightfloat = printfont.getheight(); float yfloat = e.marginbounds.top; for (decimal indexdecimal = 0m; indexdecimal < 2000m; indexdecimal += 500m) { e.graphics.drawstring("text", printfont, Brushes.Black, e.marginbounds.left, yfloat); string formattedoutputstring = indexdecimal.tostring("n"); //Measure the string using the font. SizeF fontsize = e.graphics.measurestring(formattedoutputstring, printfont); } // Determine start for number to end at column end. float column2float = 500f fontsize.width; e.graphics.drawstring(formattedoutputstring, printfont, Brushes.Black, column2float, yfloat); yfloat += lineheightfloat; McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-49

50 Displaying a Print Preview - 1 View printer s output and choose to print or cancel Helpful for testing and debugging PrintPreviewDialog component is key Add control to component tray McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-50

51 Displaying a Print Preview - 2 The PrintPreviewDialog component uses a PrintDocument component declared for printer output Assign the PrintDocument to the Document property of the PrintPreviewDialog Execute the ShowDialog method The same PrintPage event handler executes as for the PrintDocument private void fileprintpreviewmenu_click(object sender, System.EventArgs e) { // Begin the process for print preview. printpreviewdialog1.document = printallprintdocument; printpreviewdialog1.showdialog(); } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-51

52 Printing Multiple Pages The PrintDocument's PrintPage event fires once for each page Set the HasMorePages property of the PrintPageEventArgs argument to true to print more than one page McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-52