Tài liệu Adding Menus and Processing Menu Events ppt

The control, by default called menuStrip1, appears at the bottom of the form, and a menu strip containing the caption, Type Here, is added to the top of the form.. Click the Type Here ca

Adding Menus and Processing Menu Events

Microsoft Visual Studio 2005 lets you add menus and menu items to a form in two ways You can use the Visual Studio 2005 integrated development environment (IDE) and the menu editor to create a menu graphically You can also write code that creates a

MenuStrip object (MenuStrip is a class defined in the Windows Forms library), and then add ToolStripMenuItem objects to it (ToolStripMenuItem is another class in the

Windows Forms library)

Laying out a menu is only half of the story When a user clicks a command on a menu, the user expects something to happen! You activate the commands by trapping menu events and executing code in much the same way as you do for handling control events Creating a Menu

In the following exercise, you will use the graphical approach to create menus for the Middleshire Bell Ringers Association application We will cover how to manipulate and create menus programmatically later in this chapter

Create the File menu

1 Start Visual Studio 2005

2 Open the BellRingers project, located in the \Microsoft Press\Visual CSharp Step

by Step\Chapter 21\BellRingers folder in your My Documents folder This is the Middleshire Bell Ringers application It should be the same as the version that you completed in Chapter 20

3 Display MemberForm in the Design View window (Click MemberForm.cs in the Solution Explorer, and then click Designer on the View menu, or double-click MemberForm.cs in the Solution Explorer)

MemberForm appears

4 In the Toolbox, expand the Menus & Toolbars category Drag a MenuStrip control anywhere onto MemberForm

IMPORTANT

Be sure to drop the MenuStrip control onto the form, and not onto a control on the form Some controls, such as GroupBox, can have their own menus, and dropping

a menu on such a control will create a menu for that control only

The control, by default called menuStrip1, appears at the bottom of the form, and a menu strip containing the caption, Type Here, is added to the top of the form

5 Click the Type Here caption on the menu strip, type &File, and then press Enter (If the Type Here caption on the menu strip disappears, click the mainStrip1

control at the bottom of the form and the menu reappear.)

When you click the Type Here caption, a second Type Here caption appears to the right of the current item, and a third Type Here caption appears under the File menu item

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The & character in front of a letter provides fast access to that menu item when the user presses the Alt key and the letter following the & (in this case, Alt+F) This is another common convention When you press the Alt key, the F at the start of File appears with an underscore Do not use the same access key more than once on any menu because you will confuse the user (and probably the application)

6 Click the Type Here caption that appears under the File menu item, type &New, and then press Enter

Another Type Here caption appears under the New menu item

7 Click the Type Here caption under the New menu item, type &Open, and then press Enter

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If you mistype the text for a menu item, you can easily correct it Click the menu item, and then use the Properties window to change the Text property of the item

to the correct value

8 Click the Type Here caption under the Open menu item, type &Save Member, and then press Enter

9 Click the Type Here caption under the Save Member menu item, type a minus sign (–), and then press Enter

The minus sign appears as a menu separator bar used to group related menu items together

10 Click the Type Here caption under the separator bar, type &Print, and then press Enter

11 Click the Type Here caption under the Print menu item, type a minus sign (–), and then press Enter

Another separator bar appears

12 Click the Type Here caption under the second separator bar, type E&xit, and then press Enter

Notice that the conventional access key for exit is “x.” When you have finished, the menu should look like this:

Menu Strip Item Types

You have been using MenuItem controls, which are the default item type for MenuStrip objects However, you can also add combo boxes and text boxes to menus in Visual Studio 2005 applications You might have noticed that a drop-down arrow appears when hovering the mouse over the Type Here caption in a MenuStrip control If you click this drop down, you will see three items: MenuItem, ComboBox, and TextBox, as shown in the following graphic:

The combo box and text box controls in a MenuStrip behave in a similar manner to ComboBox and TextBox controls on a form, and you can set their properties in the same way that you saw in Chapter 20 However, strictly speaking they are different from the versions of the controls that you drop onto forms They are ToolStripComboBox and ToolStripTextBox controls, and are designed and optimized specifically for use in

MenuStrip controls, and other related “strip” controls, such as the ContextMenuStrip and ToolStrip controls

Setting Menu Item Properties

In the following exercise, you will set the properties of the MainMenu control and the menu items You will use the Properties window to perform these tasks

Set the menu item properties

1 Click the menuStrip1 control under the form In the Properties window, change its name to mainMenu (If the Properties window is not displayed, click Properties Window on the View menu, or press F4.)

2 Right-click the File menu item on the menu strip of MemberForm On the menu that appears, click Edit DropDownItems

The Items Collection Editor displays the names of the menu items as well as their properties

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You can use the Items Collection Editor to delete menu items, add new menu items, reorder the items in a drop-down menu, and set the properties of menu items

3 Notice the names generated for each menu item They should be the same as those listed in the following table If not, click the menu item and then change the

(Name) property using the properties displayed on the right-hand side of the Items Collection Editor

New newToolStripMenuItem

Open openToolStripMenuItem

Save Member saveMemberToolStripMenuItem

Print printToolStripMenuItem

Exit exitToolStripMenuItem

4 The access keys for menu items (such as Alt+X for the Exit command) are

available only when the menu is actually displayed Commonly accessed menu items should also have shortcut keys that the user can press at any time to invoke the corresponding command For example, the New command can usually be executed by pressing Ctrl+N in many Windows applications You can add a

shortcut key to a menu item by setting the ShortcutKeys property

5 Select the newToolStripMenuItem from the list of members, and then click

ShortcutKeys in the list of properties Check the Ctrl Modifier, and select N for the key, then press Enter

6 There is another property called ShowShortcutKeys under the ShortcutKeys

property This property determines whether the shortcut key is displayed on the menu when the application runs Verify that this property is set to True

7 Change the shortcut keys for the other menu items using the values in the

following table Ensure that the ShowShortcut property for each menu item

remains set to True

Item Shortcut

openToolStripMenuItem Ctrl+O

saveMemberToolStripMenuItem Ctrl+S

printToolStripMenuItem Ctrl+P

exitToolStripMenuItem Alt+F4

8 Menu items can be enabled and disabled (disabled items are unavailable and their text appears dimmed) depending on the current actions and context For example,

in the Middleshire Bell Ringers Association application, it would not make sense

to allow the user to use the Save Member or Print commands if there is no data to save or print

9 Select the printToolStripMenuItem item, and then click Enabled in the list of proper- ties Select the False option from the drop-down list You will write some code later to update this property to True after data has displayed

Repeat this task for the saveMemberToolStripMenuItem item

10 Click OK to close the Items Collection Editor

Test the menu

1 On the Debug menu, click Start Without Debugging to compile and run the application

2 When the form appears, click the File menu

The new menu appears

Notice that the Print and Save commands are disabled You can click any of the other commands (although they won't do anything yet)

3 Close the form You can't use the Exit command on the File menu yet; click the Close button (the ‘X’ button in the top right-hand corner of the form) instead Other Menu Item Properties

Menu items have a number of other properties The following table describes the most common ones If you want more information about the other properties, consult the documentation in the MSDN Library for Visual Studio 2005

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You can set menu item properties using the Items Collection Editor as described in the

previous exercises, or by clicking a menu item in the Designer View window and then using the Properties window

Property Description

(Name) This property is the name of the menu item

Checked

Menu items can act like check boxes and cause a check mark to appear when they are clicked Setting the Checked property to True displays a check mark, and setting it to False hides the check mark

CheckOnClick Setting the CheckOnClick property to True causes the menu item to be

checked and unchecked automatically when the user clicks it

DisplayStyle

Menu items can display images as well as text names If you set the DisplayStyle property to the value Image or ImageAndText, the image specified by the Image property will appear on the menu

Enabled

This property specifies whether the menu item is enabled or disabled If a menu item is not enabled, it appears dimmed and the user will not be able

to select it

Shortcut This property specifies the shortcut key that a user can press to execute

the corresponding menu command

ShowShortcut If this property is True, the shortcut key is displayed on the menu

alongside the text of the menu item

Text This is the text that is displayed on the menu for the menu item You can

use the & character to specify an access key

ToolTipText This property specifies the text to display as a tool tip when the user

hovers the mouse over the menu item

Visible

This property determines whether the item should be displayed on the menu It is more common to use the Enabled property to show that a menu item is present but unavailable

Menu Events

There are several different events that can occur when a user gains access to a menu item Some are more useful than others The most frequently used event is the Click event, which occurs when the user clicks the menu item You typically trap this event to

perform the tasks associated with the menu item

In the following exercise, you will learn more about menu events and how to process them You will create Click events for the New and Exit menu items The purpose of the New command is to allow the user to enter the details of a new member Therefore, until the user clicks New, all fields on the form should be disabled When the user clicks the New command on the File menu, you want to enable all the fields, reset the contents of MemberForm so that the user can start adding information about a new member, and enable the Print command

Handle menu item events

1 In the MemberForm in the Design View window, click the firstName text box In the Properties window, set the Enabled property to False Repeat this process for the lastName, towerNames, isCaptain, memberSince, yearsExperience, methods, add, and clear controls

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If you press the Shift key and click several controls they will all be selected You can then set properties, such as Enabled, to the same value for all the controls at once

2 Click the File menu, and then click New

3 In the Properties window, click the Events button Select the Click event, type newClick, and then press Enter

A new event method is created and the source code displayed in the Code And Text Editor window

4 In the body of the newClick event method, type the following statement:

this.Reset();

This calls the Reset method If you remember in Chapter 20, the Reset method resets the controls on the form to their default values (If you don't recall how the Reset method works, scroll the Code And Text Editor window to display the method and refresh your memory.)

5 You now need to enable the Save Member and Print menu items to allow the user

to save and print the current member's information You can do this by setting the Enabled property of the saveMemberToolStripMenuItem and

printToolStripMenuItem items to true

After the call to the Reset method in the newClick event method, add the

following statements:

saveMemberToolStripMenuItem.Enabled = true;

printToolStripMenuItem.Enabled = true;

6 You must also enable the controls on the form Append the following statements

to the newClick method:

7 firstName.Enabled = true;

8 lastName.Enabled = true;

9 towerNames.Enabled = true;

10 isCaptain.Enabled = true;

11 memberSince.Enabled = true;

12 yearsExperience.Enabled = true;

13 methods.Enabled = true;

14 add.Enabled = true;

clear.Enabled = true;

15 Next, you need to create a Click event method for the Exit command This method should cause the form to close Return to the Design View displaying

MemberForm, and then on the File menu, click Exit

16 In the Properties window, verify that the events are displayed and select the Click event Type exitClick, and press Enter

The exitClick event method is created and the source code displayed in the Code And Text Editor window

17 In the body of the exitClick method, type the following statement:

this.Close();

The Close method of a form attempts to close the form Notice the use of attempts

in that sentence—remember that a form might intercept the Closing event and prevent the form from closing The Middleshire Bell Ringers Association

application does precisely this, and asks the user if he or she wants to quit If the user says no, the form does not close and the application continues to run

Test the menu events

1 On the Debug menu, click Start Without Debugging to compile and run the

application

Notice that all the fields on the form are disabled

2 Click the File menu

The Print and Save commands are disabled

3 Click New Click the File menu again

The Print and Save commands are now enabled, as are all the fields on the form

4 Click Exit The form tries to close You are asked if you are sure you want to close the form If you click No, the form remains open; if you click Yes, the form closes and the application finishes

5 Click Yes to close the form