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Lesson 2: Using User Assistance Controls and Components 575 Table 12-6 Important Methods of the HelpProvider Component SetHelpKeyword Sets the keyword for a control, such as an index

Lesson 2: Using User Assistance Controls and Components 575

Table 12-6 Important Methods of the HelpProvider Component

SetHelpKeyword Sets the keyword for a control, such as an index keyword or

a topic keyword This keyword will be passed to the help file

when help is shown The HelpNavigator setting determines

how the keyword is used

SetHelpNavigator Sets the HelpNavigator for a control This property deter­

mines how the help file is displayed

SetHelpString Sets the help string for a control If the HelpNamespace prop­

erty is not set to a file, the help string will be displayed in a popup box over the control when the F1 button is pressed

SetShowHelp Sets whether help is shown for a particular control

Setting the HelpNavigator The SetHelpNavigator method allows you to determine how help is displayed for a particular control The SetHelpNavigator method requires two parameters: a control that the HelpNavigator will be set for, and a member of the

HelpNavigator enumeration The following example demonstrates how to set the Navigator for a Button control named Button1:

Help-' VB

HelpProvider1.SetHelpNavigator(Button1, HelpNavigator.Find)

// C#

helpProvider1.SetHelpNavigator(Button1, HelpNavigator.Find);

Table 12-7 describes the members of the HelpNavigator enumeration

Table 12-7 Members of the HelpNavigator Enumeration

576 Chapter 12 Enhancing Usability

Table 12-7 Members of the HelpNavigator Enumeration

KeywordIndex The help file opens to the topic with the specified keyword if one

exists; otherwise, the index entry closest to the specified key­word is displayed

TableOfContents The help file opens to the table of contents

Topic The help file opens to a specified topic if the topic exists

TopicId The help file opens to a topic indicated by a numeric topic identifier

Configuring Help for a Control The following example demonstrates how to use the

HelpProvider component to configure help for a control named Button1

' VB

// C#

Playing Sound Files and System Sounds

Sound files and system sounds can be used to communicate information or alerts to

your users The SoundPlayer class in the System.Media namespace encapsulates all of

the functionality required to play sound files

� To play a sound file with the SoundPlayer class

1 Create an instance of the SoundPlayer class that specifies the sound file to be

played, as shown here:

Lesson 2: Using User Assistance Controls and Components 577

You can play system sounds by accessing the System.Media.SystemSounds class This

class contains members that represent each of the system sounds, and they can be

played by calling the Play method

� To play a system sound

Call the Play method of the appropriate system sound, as shown here:

' VB

System.Media.SystemSounds.Beep.Play()

// C#

System.Media.SystemSounds.Beep.Play();

Using the Timer Component to Raise an Event at Regular Intervals

The Timer component allows you raise the Timer.Tick event at regular intervals By

writing code to handle this event, you can schedule your application to call methods

or take other actions at predefined intervals For example, you might want to display

the current time in a Label control and update it every minute

The key property of the Timer component is the Interval property The Interval prop­ erty specifies the number of milliseconds between intervals of the Tick event For example, if the Interval property is set to 2000, the Tick event will be raised every two seconds The Interval property can be set in the Properties window or in code, as

shown in the following example:

' VB

Timer1.Interval = 2000

// C#

timer1.Interval = 2000;

578 Chapter 12 Enhancing Usability

Another important property of the Timer component is the Enabled property If the

Enabled property is set to False, the Timer.Tick event will not be raised When the Enabled property is set to True, the Timer.Tick event will be raised at a frequency deter­

mined by the Interval property

The Timer.Start and Timer.Stop methods allow you to start and stop the Timer, respec­ tively These methods are simply shorthand ways of setting the Enabled property Call­ ing the Timer.Start method sets the Timer.Enabled property to True and commences regular firing of the Tick event Calling the Timer.Stop method sets the Timer.Enabled property to False and ceases firing of the Tick event

The following example demonstrates a handler for the Timer.Tick event This sample code updates the text in Label1 with the current time every time the Tick event is raised

' VB

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As _

System.EventArgs) Handles Timer1.Tick

Using the HScrollBar and VScrollBar Controls

The HScrollBar and VScrollBar controls are controls that are designed to provide easy

navigation through a long list of items or values by scrolling within an application or

control The HScrollBar control represents a horizontal scroll bar and the VScrollBar

control represents a vertical scroll bar, but the two controls function identically other­

wise The ScrollBar controls consist of two scrollbar buttons at either end of the con­

trol, a slider, and a slider track in which the slider can move The user can position the

slider and thereby change the Value property

The ScrollBar controls are distinct from the scrollbars that appear in Forms or scrollable

controls—those scroll bars are integral parts of the control or form that they function

with The ScrollBar controls are designed for independent operation or operation with controls that do not normally have scrollbars, such as the PictureBox control The important properties of the ScrollBar controls are shown in Table 12-8

Lesson 2: Using User Assistance Controls and Components 579

Table 12-8 Important Properties of the Scrollbar Controls

Property Description

LargeChange The amount the Value property changes when the user presses the

PageUp or PageDown keys or clicks in the ScrollBar track

Maximum The maximum value for the scrollbar In HScrollBar, the Value

property is equal to the Maximum property when the scrollbar slider is all the way to the right in the scroll track In VScrollBar, the

Value property is equal to the Maximum property when the

scroll-bar slider is all the way at the bottom of the scroll track

Minimum The minimum value for the scrollbar In HScrollBar, the Value prop­

erty is equal to the Minimum property when the scrollbar slider is all the way to the left in the scroll track In VScrollBar, the Value property is equal to the Minimum property when the scrollbar

slider is all the way at the top of the scroll track

SmallChange The amount the Value property changes when the user presses one

of the arrow keys or clicks a scrollbar button

Value The current value of the Scrollbar control This property reflects

the current location of the scrollbar slider

Persisting Application Settings Between Sessions

The NET Framework allows you to persist property values between user sessions in the form application settings and access and change those settings at run time You might, for example, create settings that determine the color scheme of your applica­tion or settings that “remember” user names or data connection strings

Persisting settings is a two-step process First, you create a setting and give it a unique name and a value The value can be any object and should be appropriate for the prop­erty that you want to persist Second, the property that you want to persist is bound

to the setting At run time, the settings can be accessed, changed, and saved if need be

Creating Settings at Design Time Visual Studio 2005 provides user interface tools that allow you to create settings quickly and easily You can use the Settings editor (shown in Figure 12-2) to create and edit new settings

580 Chapter 12 Enhancing Usability

Figure 12-2 The Settings editor for creating and editing new settings

The Settings editor has four properties that must be set when they are created The

Name must be unique in the application The Type property represents the type of set­

ting, which should be appropriate for the property you want to bind it to The Scope property must be set to either Application or User Settings that are scoped for the

application are read-only at run time and cannot be changed by the user Settings that are scoped for the user are read-write at run time and can be changed and saved by the user Finally, a value must be provided for the setting This value must be of the type

indicated by the Type property

� To create a setting at design time

1 In Solution Explorer, right-click the project and choose Properties

2 In the main window, select the Settings tab

3 Set the Name, Type, Scope, and Value for the new setting

4 If your application has not yet been saved, choose Save All from the File menu to

save your application

Once a setting has been created, you can bind it to a property in the Properties window

� To bind a setting to a property at design time

1 In the Properties window for a control, expand (ApplicationSettings) and then click

the button next to (PropertyBinding) to open the Application Settings window

2 Locate the property that you want to bind to a setting Select the appropriate set­

ting from the drop-down box to the right of the property name If no appropriate setting exists, you can create a new setting by clicking the (New…) link in the bot­tom of the drop-down box

Lesson 2: Using User Assistance Controls and Components 581

Accessing Settings at Run Time You can read the values of your settings at run time and change and save the values of user-scoped settings In Visual Basic, settings are

exposed via the My object, and changes made to any user-scoped settings values are automatically saved In C#, you can access settings through the Properties.Set­

tings.Default object, but any changes made must be saved manually At design time,

individual settings appear in Intellisense as properties of the Settings object and can be

treated in code as such The following example demonstrates how to change the

value of a user-scoped string setting named TitleSetting:

1 What is the purpose of the Timer component?

2 What is the purpose of the ErrorProvider component?

Quick Check Answers

1 The Timer component is used to execute code at regular intervals

2 The error provider is used to provide a visual cue to users when a validation

error occurs

Lab: Practice with User Assistance Controls

In this lab, you will create a small application that uses a timer to display and update the current time in a label, and you will use the functionality and many of the controls that have been discussed in this lesson Although the end result of the lesson is some­what contrived, it will allow you to practice with the different aspects of this lesson

� Exercise 1: Creating a Simple Digital Clock

1 In Visual Studio, create a new Windows Forms application

2 From the Toolbox, drag a Label control and a Timer component onto the form

3 Select the Timer component In the Properties window, set the Interval property

to 1000 and the Enabled property to True

4 In the Designer, double-click the Timer component to open the default event

handler for the Timer1.Tick event Add the following code to this method:

582 Chapter 12 Enhancing Usability

' VB

Label1.Text = Now.ToLongTimeString

// C#

label1.Text = System.DateTime.Now.ToLongTimeString();

5 Press F5 to compile and run your application Note that the current time is

updated in the Label control every second

� Exercise 2: Using the PropertyGrid

1 From the Toolbox, drag a PropertyGrid control onto the form that you created in

the last exercise

2 In the Properties window, set the Dock property of the PropertyGrid control to

Right

3 In the Properties window, set the SelectedObject property of the PropertyGrid con­

trol to Timer1

4 Press F5 to compile and run the application You can now set the properties of

the Timer at run time via the PropertyGrid control

� Exercise 3: Providing Tooltips for Your Application

1 From the Toolbox, drag a ToolTip component onto the form you created in Exer­

cise 1, “Creating a Simple Digital Clock.”

2 Select Label1 In the Properties window, set the tooltip on ToolTip1

3 Press F5 to compile and run your application Note that your label now has a

tooltip associated with it

� Exercise 4: Using Settings

1 In Solution Explorer, for the application you started in Exercise 1, right-click the

project and choose Properties

2 In the Properties pane, choose the Settings tab

3 In the Settings window, create a setting with the following properties:

Lesson 2: Using User Assistance Controls and Components 583

4 In the Designer, select Timer1 In the Properties window, expand (Application

Settings) and then click the button next to (PropertyBinding) to open the Appli­cation Settings window

5 In the Application Settings window, bind the Interval property to the IntervalSetting

setting

6 In the Designer, select the Form In the Properties window, click the events but­

ton to list the events for the form Double-click the cell next to the FormClosing event to open the default event handler for the Form1.FormClosing event Add the

following code to this event handler:

7 From the File menu, choose Save All

8 Press F5 to compile and run your application Any changes that you make to the

interval property will be persisted between sessions

Lesson Summary

■ The PropertyGrid control allows you to set properties for controls in your appli­ cation through a grid-style user interface The SelectedObject property indicates

the object for which the properties can be set

■ The ProgressBar control allows you to inform the user about progress for consuming processes such as file downloads The Minimum and Maximum prop­ erties represent the minimum and maximum values for the ProgressBar, and the

time-Value control represents the current value

■ The StatusStrip control is a ToolStrip control that is designed to display information about the status of the application ToolStripStatusLabel and ToolStripProgressBar are ToolStripItem controls that are designed to work with the StatusStrip

■ The ToolTip component allows you to display tooltips for the controls on your

form

■ The ErrorProvider component allows you to display errors in user input in your application You can validate user input by adding code to the Validating event handler If the user input is not valid, use the SetError method of the error pro­

vider to set the error

584 Chapter 12 Enhancing Usability

■ The HelpProvider component enables you to integrate HTML Help 1.x files (.chm and htm) with your application The HelpNamespace property represents the location of the help file that is associated with the HelpProvider component You can call SetShowHelp to set F1 help for a control and SetHelpKeyword to set the

keyword that will be passed on to the help file

■ The SoundPlayer component allows you to play sound files You can use the

System-Sounds class to play system sounds at run time

■ The Timer component allows you to execute actions at regular intervals You can handle the Timer.Tick event to define code that is executed at regular intervals The Interval property determines how frequently the Timer.Tick event is raised

■ The HScrollBar and VScrollBar controls are designed to provide a user interface

that allows rapid access to a large range of values or a long list of options The

Minimum and Maximum properties represent the minimum and maximum val­

ues for the control; the Value property represents the current value and is tied to

the current position of the slider

■ Application settings allow you to persist settings between application settings Application-scoped settings are read-only and user-scoped settings are read-

write at run time You can access settings via the My.Settings object in Visual Basic or the Properties.Settings.Default object in C#

Lesson Review

The following questions are intended to reinforce key information presented in this lesson The questions are also available on the companion CD if you prefer to review them in electronic form

NOTE Answers

Answers to these questions and explanations of why each choice is right or wrong are located in the “Answers” section at the end of the book

1 Which of the following code examples will advance the value of a progress bar

named ProgressBar1 by 10? (Choose all that apply.)

A ' VB

// C#

Lesson 2: Using User Assistance Controls and Components 585

2 Given a TextBox control, an ErrorProvider component, and a validation routine in

the Validating event handler for that text box, which of the following is required

to complete the validation routine and display an error icon when the user input

is not valid? (Choose all that apply.)

A Set the CausesValidation property for other controls on the form to True

B Call the ErrorProvider.SetError method and set the error to an informative

string when user input is not valid

C Call the ErrorProvider.SetError method and set the error to an empty value

when user input is valid

D Call the ErrorProvider.Validate method to validate the text box input

3 Given a TextBox control named TextBox1 and a HelpProvider control named

HelpProvider1 with the HelpNamespace property set to an appropriate help file,

which of the following code samples will cause the search page for help to be dis­

played when the F1 key is pressed and TextBox1 has the focus?

// C#

helpProvider1.SetShowHelp(textBox1, true);

helpProvider1.SetHelpString(textBox1, “Search”);

Chapter 12 Review 587

Chapter Review

To further practice and reinforce the skills you learned in this chapter, you can per­form the following tasks:

■ Review the chapter summary

■ Review the list of key terms introduced in this chapter

■ Complete the case scenarios These scenarios set up real-world situations involv­ing the topics of this chapter and ask you to create a solution

■ Complete the suggested practices

■ Take a practice test

Chapter Summary

■ Applications should be designed to support the principles of accessibility Appli­cations should support the standard system settings, they should be designed to have a variety of inputs, and they should convey no information solely by sound Each control exposes several accessibility properties that are used by accessibil­ity aids to gather and display information

■ The PropertyGrid control allows you to set properties for controls in your appli­ cation through a grid-style user interface The ProgressBar control allows you to inform the user about progress for time-consuming processes The StatusStrip control is a ToolStrip control that is designed to display information about the

status of the application

■ The ToolTip, ErrorProvider, and HelpProvider components provide additional design-time properties for controls on the form The ToolTip component allows you

to display tooltips for the controls on your form The ErrorProvider component allows you to display errors in user input in your application The HelpProvider

component enables you to integrate HTML Help 1.x files with your application

■ The SoundPlayer component allows you to play sound files The Timer compo­ nent allows you to execute actions at regular intervals The HScrollBar and

VScrollBar controls are designed to provide a user interface that allows rapid

access to a large range of values or a long list of options

■ Application settings allow you to persist settings between application settings

You can access settings via the My.Settings object in Visual Basic or the Properties

.Settings.Default object in C#

of the functionality is complete You have been tasked with making the user interface friendlier The following are your key requirements

■ Application must support high-contrast mode

■ Application must be accessible to hearing-impaired users

■ Application must be accessible to users who are unable to use a mouse

■ Application must work well with all standard usability aids

Questions

What strategies can you use to implement these requirements in this application?

Suggested Practices

■ Create an application that allows you to browse sound files on your computer

and play them with the SoundPlayer component

■ Extend the application created in the lab in Lesson 2, “Practice with User Assis­tance Controls,” to include F1 help and validation for property values

Take a Practice Test

The practice tests on this book’s companion CD offer many options For example, you can test yourself on just the content covered in this chapter, or you can test yourself on all the 70-526 certification exam content You can set up the test so that it closely sim­ulates the experience of taking a certification exam, or you can set it up in study mode

so that you can look at the correct answers and explanations after you answer each question

MORE INFO Practice tests

For details about all the practice test options available, see “How to Use the Practice Tests” in this book’s Introduction

Exam objectives in this chapter:

■ Run a background process by using the BackgroundWorker component

■ Announce the completion of a background process by using the

Background-Worker component

■ Cancel a background process by using the BackgroundWorker component

■ Report the progress of a background process by using the BackgroundWorker

component

■ Request the status of a background process by using the BackgroundWorker

component

■ Implement advanced asynchronous techniques

■ Create an asynchronous method

■ Create a new process thread

Lessons in this chapter:

■ Lesson 1: Managing a Background Process with the

BackgroundWorker Component 593

■ Lesson 2: Implementing Asynchronous Methods 605

591

592 Chapter 13 Asynchronous Programming Techniques

Before You Begin

To complete the lessons in this chapter, you must have:

■ A computer that meets or exceeds the minimum hardware requirements listed in the “Introduction” at the beginning of the book

■ Visual Studio 2005 Professional Edition installed on your computer

■ An understanding of Visual Basic or C# syntax and familiarity with the NET Framework

Real World

Matt Stoecker

Even with ever increasing processor speeds, time-consuming tasks are still a cen­tral part of many of the applications I write Before Visual Studio 2005, creating asynchronous operations was difficult and time-consuming With the introduc­

tion of the BackgroundWorker component, creating simple asynchronous opera­

tions is easily accessible to programmers of all levels For more advanced operations, delegates and threads provide the level of functionality needed

Lesson 1: Managing a Background Process with the BackgroundWorker Component 593

Lesson 1: Managing a Background Process with the

BackgroundWorker Component

Frequently you are required to perform tasks that consume fairly large amounts of

time, such as file downloads The BackgroundWorker component provides an easy way

to run time-consuming processes in the background, thereby leaving the user inter­face responsive and available for user input

After this lesson, you will be able to:

■ Run a background process by using the BackgroundWorker component

■ Announce the completion of a background process by using the BackgroundWorker

component

■ Cancel a background process by using the BackgroundWorker component

■ Report the progress of a background process by using the BackgroundWorker

component

■ Request the status of a background process by using the BackgroundWorker

component

Estimated lesson time: 45 minutes

The BackgroundWorker component is designed to allow you to execute time-consuming

operations on a separate, dedicated thread This allows you to run operations that take extended periods of time, such as file downloads and database transactions, asynchronously and allow the user interface to remain responsive

The key method of the BackgroundWorker component is the RunWorkerAsync method When this method is called, the BackgroundWorker component raises the DoWork event The code in the DoWork event handler is executed on a separate, dedicated

thread, allowing the user interface to remain responsive Important members of the

BackgroundWorker component are shown in Table 13-1

Table 13-1 Important Members of the BackgroundWorker Component

CancellationPending Property Indicates whether the application has

requested cancellation of a background operation

IsBusy Property Indicates whether the BackgroundWorker

is currently running an asynchronous operation

594 Chapter 13 Asynchronous Programming Techniques

Table 13-1 Important Members of the BackgroundWorker Component

WorkerReportsProgress Property Indicates whether the BackgroundWorker

component can report progress updates

WorkerSupportsCancellation Property Indicates whether the BackgroundWorker

component supports asynchronous cancellation

CancelAsync Method Requests cancellation of a pending back­

ground operation

ReportProgress Method Raises the ProgressChanged event

RunWorkerAsync Method Starts the execution of a background oper­

ation by raising the DoWork event

DoWork Event Occurs when the RunWorkerAsync method is

called Code in the DoWork event handler is run on

a separate and dedicated thread

ProgressChanged Event Occurs when ReportProgress is called

RunWorkerCompleted Occurs when the background operation has been

completed, cancelled, or has raised an exception

Running a Background Process

The RunWorkerAsync method of the BackgroundWorker component starts the execu­ tion of the background process by raising the DoWork event The code in the DoWork

event handler is executed on a separate thread The following procedure explains how

to create a background process

� To create a background process with the BackgroundWorker component

1 From the Toolbox, drag a BackgroundWorker component onto the form

2 In the component tray, double-click the BackgroundWorker component to create

the default event handler for the DoWork event Add the code that you want to

run on the separate thread An example is shown below

' VB

Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal _

e As System.ComponentModel.DoWorkEventArgs) Handles _ BackgroundWorker1.DoWork

' Insert time-consuming operation here

Lesson 1: Managing a Background Process with the BackgroundWorker Component 595

3 Elsewhere in your code, start the time-consuming operation on a separate thread

by calling the RunWorkerAsync method, as shown:

' VB

BackgroundWorker1.RunWorkerAsync()

// C#

backgroundWorker1.RunWorkerAsync();

Providing Parameters to the Background Process

Sometimes you will want to run a background process that requires a parameter For example, you might want to provide the address of a file for download You can

provide a parameter in the RunWorkerAsync method This parameter will be avail­ able as the Argument property of the instance of DoWorkEventArgs in the DoWork

event handler

� To provide a parameter to a background process

1 Include the parameter in the RunWorkerAsync call, as shown below:

' VB

RunWorkerAsync("C:\myfile.txt")

// C#

RunWorkerAsync("C:\\myfile.txt");

2 Retrieve the parameter from the DoWorkEventArgs.Argument property and cast it

appropriately to use it in the background process An example is shown below:

' VB

Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal _

e As System.ComponentModel.DoWorkEventArgs) Handles _

BackgroundWorker1.DoWork

Dim myPath As String

myPath = CType(e.Argument, String)

‘ Use the argument in the process

596 Chapter 13 Asynchronous Programming Techniques

}

Announcing the Completion of a Background Process

When the background process terminates, whether because the process is completed

or cancelled, the RunWorkerCompleted event is raised You can alert the user to the completion of a background process by handling the RunWorkerCompleted event An

example is shown below:

You can ascertain if the background process was cancelled by reading the e.Cancelled

property, as shown below:

Lesson 1: Managing a Background Process with the BackgroundWorker Component 597

System.Windows.Forms.MessageBox.Show("Process completed");

}

}

Returning a Value from a Background Process You might want to return a value from

a background process For example, if your process is a complex calculation you

would want to return the end result You can return a value by setting the Result prop­ erty of the DoWorkEventArgs in the DoWorkEventHandler This value will then be avail­ able in the RunWorkerCompleted event handler as the Result property of the

RunWorkerCompletedEventArgs parameter, as shown in the following example:

Cancelling a Background Process

You might want to implement the ability to cancel a background process Back­

groundWorker supports the ability to cancel a background process, but you must

implement must of the cancellation code yourself The WorkerSupportsCancellation property of the BackgroundWorker component indicates whether the component

598 Chapter 13 Asynchronous Programming Techniques

supports cancellation You can call the CancelAsync method to attempt to cancel the operation; doing so sets the CancellationPending property of the BackgroundWorker component to True By polling the CancellationPending property of the Background-

Worker component, you can determine whether or not to cancel the operation

� To implement cancellation for a background process

1 In the Properties window, set the WorkerSupportsCancellation property to True to

enable the BackgroundWorker component to support cancellation

2 Create a method that is called to cancel the background operation The following

example demonstrates how to cancel a background operation in a Button.Click

event handler

' VB

Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As _

System.EventArgs) Handles btnCancel.Click BackgroundWorker1.CancelAsync()

End Sub

// C#

3 In the BackgroundWorker.DoWork event handler, poll the BackgroundWorker.Can­

cellationPending property, and implement code to cancel the operation if it is True You should also set the e.Cancel property to True as shown in the following

example:

' VB

Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal _

e As System.ComponentModel.DoWorkEventArgs) Handles _ BackgroundWorker1.DoWork

For i As Integer = 1 to 1000000 TimeConsumingMethod()

// C#

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)

Lesson 1: Managing a Background Process with the BackgroundWorker Component 599

Reporting Progress of a Background Process with BackgroundWorker

For particularly time-consuming operations, you might want to report progress back

to the primary thread You can report progress of the background process by calling

the ReportProgress method This method raises the BackgroundWorker.ProgressChanged

event and allows you to pass a parameter that indicates the percentage of progress that has been completed to the methods that handle that event The following exam­

ple demonstrates how to call the ReportProgress method from within the

Background-Worker.DoWork event handler and then update a ProgressBar control in the BackgroundWorker.ProgressChanged event handler