chapter 5 menus, common dialog boxes, and methods programming in c#.net © 2003 by the mcgraw-hill...
TRANSCRIPT
Chapter 5 Menus, Common Dialog
Boxes, and Methods
Programming in C# .NET
© 2003 by The McGraw-Hill Companies, Inc. All rights reserved.
© 2003 by The McGraw-Hill Companies, Inc. All rights reserved.5- 2
Objectives
• Create menus and submenus for program control
• Display and use the Windows common dialog boxes
• Write reusable code in methods and call the methods from other locations
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Menus
• Consist of a menu bar containing menus with list of menu items
• Use menu items in place of or in addition to buttons to activate a method
• Menu items are controls with properties and events
• Create menus with the Visual Studio Menu Designer
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Defining Menus
• Add a MainMenu control to a form from the toolbox
• The MainMenu control appears in the component tray
• Enter text at words Type Here
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The Text and Name Properties
• The Text property holds the words that appear on the screen
• Use the ampersand (&) to specify the key for keyboard access in the Text property
• The Name property gives the MenuItem a name• To assign a Name, append suffix “Menu” for top-
level menu names and “MenuItem” for items on the menu
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Submenus
• A new list that pops up under an item on a menu is called a submenu
• A filled triangle to the right of a menu item indicates a submenu for that menu item
• Create a submenu by moving to the right of a menu item and typing the next item’s text
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Separator Bars
• A separator bar in a menu groups menu items according to their purpose
• Two ways to create a separator bar– Type a single hyphen (-) for the text– Right-click on Menu Designer at separator bar
position and choose Insert Separator
• Keep the default Name property of the separator bar control
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Creating a Menu – Step-by-Step
You are going to create a project with one form and a menu bar that contains these menu items:
File Help
Exit About
1. Create the Menu Items
2. Change the Properties of the Menu Items
3. Write the Code• Double-click on a menu item to open the Editor window in the
control’s Click event-handling method
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Modifying Menu Items
• Use the Menu Designer to modify menu items– Right-click on the menu bar for options
including Delete, Insert New, Insert Separator, and Edit Names
– Drag and drop menu items to rearrange
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The Enabled Property
• The Enabled property is true by default
• An enabled menu item has black text and is available for selection
• A disabled menu item is grayed out and not available
• Set the Enabled property at design time or in code at run time
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The Checked Property
• A menu item may contain a check mark next to it to indicate the option is currently selected
• By default, the Checked property is set to false
• Change the Checked property at design time or in code at run time
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Setting Keyboard Shortcuts
• Create keyboard shortcuts for your menu items– Select the menu item in the designer– Select the Shortcut property in the Properties
window– Select choice from drop down list
• ShowShortcut property is true by default
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Standards for Windows Menus
• Include keyboard access keys and stick with the standard key assignments
• Place the File menu on the left end of the menu bar with an Exit command at the end
• If there is a Help menu, it should be at the right end of the menu bar
• Any menu item that will display a dialog box should have “…” appended to its Text property
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Common Dialog Boxes
• Common dialog controls are used to display dialog boxes that are provided with Windows
• Visual Studio .NET supports the following common dialog controls- OpenFileDialog - SaveFileDialog- FontDialog - ColorDialog- PrintDialog - PrintPreviewDialog
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Displaying a Common Dialog Box
• Use the ShowDialog method• Example: ColorDialog1.ShowDialog();
• A modal dialog box stays on top of the application and must be responded to– Use the ShowDialog method
• A modeless dialog box does not require a response– Use the Show method
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Using the Information from the Dialog Box
• Color Dialog Box– The color selected by user stored in the Color property
– Assign this property to another object
• Font Dialog Box– The font selected by user stored in the Font property
– Assign this property to another object
• Initialize the Font or Color property to an existing value– Example: FontDialog1.Font = subTotalLabel.Font;
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Creating Context Menus
• Context menus are the shortcut menus that pop up when you right-click on an object
• Items on a context menu are generally specific to that object
• Add a ContextMenu control to the form
• Click on words Context Menu then Type Here to add menu items
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Creating Context Menus cont.
• An application can have more than one context menu
• Assign the context menu to a form or control with the ContextMenu property
• If there is only one context menu, attach it to the form
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Creating a Context Menu – Step-by-Step
You are going to create a context menu that contains these menu items:
Color…Font…Exit…
1. Add the Context Menu to a Form2. Test the Program
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Writing General Methods
• A general method contains reusable code that is called from other methods
• The method may return a value or not– If a value is returned, specify the return type
before the method name– If no value is returned, use the keyword void
before the method name
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Creating a New Method
• Write a method header and enclose the lines of code within a set of braces
• Example:private void SelectColor()
{
//Display the color dialog box
ColorDialog1.ShowDialog();
}
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Creating a New Method cont.
• You must specifically call the method from another method
• Example:private void changeButtonMessage_Click(object
sender, System.EventArgs e)
{
//Change the color of the message
SelectColor();
messageLabel.ForeColor = ColorDialog1.Color;
}
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Passing Arguments to Methods
• Use arguments when you need to use the value of a variable in one method and also in a second method that is called from the first
• Any arguments defined in a method must be supplied in a call to that method
• The argument value must be the same data type in both locations
• The name of an argument does not have to be the same in both locations
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Writing Methods That Return Values
• Write a method that will calculate a value and return it to the place where the method was called
• The type of data returned is defined in the method header
• A method can return a value and use one or more arguments
• The name given an argument in the header is the name used to refer to that argument inside the method
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Returning the Result of a Method
• The return value is passed back with a Return statement
• The keyword Return is followed by a variable or expression containing the value to return to the caller
• If the method header specifies void, no Return statement is required
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Method Header Format
Method name Argument data type
Return data type Argument
Access modifier
private decimal Commission(decimal decSalesAmount)
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Methods with Multiple Arguments
• The sequence and data type of the arguments in the call must exactly match the arguments in the method header
• The list of zero or more arguments is enclosed in parentheses
• When you call the method, the Visual Studio .NET smart editor displays the arguments of your method
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Breaking Calculations into Smaller Units
• Projects with many calculations can be easier to understand and write if broken down into small units
• Each unit should perform one program function or block of logic
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Your Hands-On Programming Example
Modify the hands-on programming example from Chapter 4 by replacing some of the buttons with menus. Write a method to calculate the sales tax and allow the user to select the font and color of the summary labels.
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Summary
• The Visual Studio Menu Designer enables you to create menus, menu items, and submenus, each with keyboard access keys.
• In the Menu Designer you can set and modify the order and level of menu items.
• Each menu item has a Click event. The code to handle selection of a menu item belongs in the item’s Click event-handling method.
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Summary cont.
• Common dialog boxes allow C# programs to display the predefined Windows dialog boxes for Print, PrintPreview, File Open, File Save, Fonts, and Colors.
• Context menus, or shortcut menus, are created using a ContextMenu control and the Menu Designer. Context menus pop up when the user right-clicks.
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Summary cont.
• The programmer can write reusable code in general methods. These methods can be called from any other method in the form class.
• Methods that return a value must specify the data type of the return value and set the value to return using a return statement. If the return type is void, no value can be returned.