Chapter 7 · Chapter 7 Lists, Loops, and ... –Determines whether list box has a text box for user...

McGraw-Hill © 2010 The McGraw-Hill Companies, Inc. All rights reserved.

Chapter 7

Lists, Loops, and Printing

McGraw-Hill © 2010 The McGraw-Hill Companies, Inc. All rights reserved. 7-2

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


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


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



• 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


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


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


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


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


Using the Properties Window - 2


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


The Items.Add Method

• General Form

• Examples

• Use the Items.Add method to add a value entered in the text box portion of a combo box (not automatically added)

• Add contents of a text box to a list box

Object.Items.Add(ItemValue);

schoolsListBox.Items.Add("Harvard");

schoolsListBox.Items.Add("Stanford");

schoolsListBox.Items.Add(schoolsTextBox.Text);

majorsComboBox.Items.Add(majorsComboBox.Text);

majorsComboBox.Items.Add(majorString);

coffeeComboBox.Items.Add(coffeeComboBox.Text);

schoolsListBox.Items.Add(schoolTextBox.Text);


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


The Items.Insert Method

• General Form

• Examples

Object.Items.Insert(IndexPosition, ItemValue);

schoolsListBox.Items.Insert(0, "Harvard");

majorsComboBox.Items.Insert(1, majorsComboBox.Text);


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;


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


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


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”;


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);


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(); }


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


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



• 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). }



• 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


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. }


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


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


The for Statement Examples

• 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

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– –)


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. }


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.

}


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;

}


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


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()); }


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


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


The PrintDocument Component

• Set up output for

the printer using

methods and

events of the

PrintDocument

component

– Appears in

component tray


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


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


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


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


The DrawString Method

• General Form (One simple argument

list)

• Examples

GraphicsObject.DrawString(StringToPrint, Font, Brush, Xcoordinate, Ycoordinate);

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);


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;


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;


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


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; }


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);


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


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; }


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


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(); }


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

Chapter 7 · Chapter 7 Lists, Loops, and ... –Determines whether list box has a text box for user...

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