Home > Articles > Programming > Visual Basic

This chapter is from the book

Writing the Code Behind an Interface

You have to write code for the program to be capable of performing tasks and responding to user interaction. Visual Basic is an event-driven language, which means that code is executed in response to events. These events might come from users, such as a user clicking a button and triggering its Click event, or from Windows itself (see Hour 4, “Understanding Events,” for a complete explanation of events). Currently, your application looks nice, but it won’t do anything. Users can click the Select Picture button until they can file for disability with carpal tunnel syndrome, but nothing will happen, because you haven’t told the program what to do when the user clicks the button. You can see this for yourself now by pressing F5 to run the project. Feel free to click the buttons, but they don’t do anything. When you’re finished, close the window you created to return to Design mode.

You write code to accomplish two tasks. First, you write code that lets users browse their hard drives to locate and select a picture file and then display it in the picture box. (This sounds a lot harder than it is.) Second, you add code to the Quit button that shuts down the program when the user clicks the button.

Letting a User Browse for a File

The first bit of code you’ll write enables users to browse their hard drives, select a picture file, and then see the selected picture in the PictureBox control. This code executes when the user clicks the Select Picture button; therefore, it’s added to the Click event of that button.

When you double-click a control on a form in Design view, the default event for that control is displayed in a code window. The default event for a Button control is its Click event, which makes sense, because clicking is the most common action a user performs with a button. Double-click the Select Picture button now to access its Click event in the code window (see Figure 1.12).

FIGURE 1.12

FIGURE 1.12 You’ll write all your code in a window such as this.

When you access an event, Visual Basic builds an event handler, which is essentially a template procedure in which you add the code that executes when the event occurs. The cursor is already placed within the code procedure, so all you have to do is add code. Although this may seem daunting, by the time you’re finished with this book, you’ll be madly clicking and clacking away as you write your own code to make your applications do exactly what you want them to do—well, most of the time. For now, just enter the code as I present it here.

It’s important that you get in the habit of commenting your code, so the first statement you’ll enter is a comment. Beginning a statement with an apostrophe (’) designates that statement as a comment. The compiler won’t do anything with the statement, so you can enter whatever text you want after the apostrophe. Type the following statement exactly as it appears, and press the Enter key at the end of the line:

' Show the open file dialog box.

The next statement you enter triggers a method of the OpenFileDialog control that you added to the form. Think of a method as a mechanism to make a control do something. The ShowDialog() method tells the control to show its Open dialog box and let the user select a file. The ShowDialog() method returns a value that indicates its success or failure, which you’ll then compare to a predefined result (DialogResult.OK). Don’t worry too much about what’s happening here; you’ll learn the details of all this in later hours. The sole purpose of this hour is to get your feet wet. In a nutshell, the ShowDialog() method is invoked to let a user browse for a file. If the user selects a file, more code is executed. Of course, there’s a lot more to using the OpenFileDialog control than presented in this basic example, but this simple statement gets the job done. Enter the following statement and press Enter to commit the code. (Don’t worry about capitalization; Visual Basic will fix the case for you.)

If ofdSelectpicture.ShowDialog = DialogResult.OK Then

It’s time for another comment. The cursor is currently between the statement that starts with If and the End If statement. Leave the cursor there and type the following statement, remembering to press Enter at the end of the line:

' Load the picture into the picture box.

This next statement, which appears within the If construct (between the If and End If statements), is the line of code that actually displays the picture in the picture box.

Type the following statement and press Enter:

picShowPicture.Image = Image.FromFile(ofdSelectPicture.Filename)

In addition to displaying the selected picture, your program will also display the path and filename of the picture on the title bar. When you first created the form, you changed its Text property in the Properties window. To create dynamic applications, properties need to be constantly adjusted at runtime, and you do this using code. Insert the following two statements, pressing Enter at the end of each line:

' Show the name of the file in the form's caption.
Me.Text = "Picture Viewer (" & ofdSelectPicture.FileName & ")"

After you’ve entered all the code, your editor should look like that shown in Figure 1.13.

FIGURE 1.13

FIGURE 1.13 Make sure that your code exactly matches the code shown here.

Terminating a Program Using Code

The last bit of code you’ll write terminates the application when the user clicks the Quit button. To do this, you need to access the Click event handler of the btnQuit button. At the top of the code window are two tabs. The current tab says ViewerForm.vb*. This tab contains the code window for the form that has the filename ViewerForm.vb. Next to this is a tab that says ViewerForm.vb [Design]*. Click this tab to switch from Code view to the form designer. If you receive an error when you click the tab, the code you entered contains an error, and you need to edit it to make it the same, as shown in Figure 1.13. After the form designer appears, double-click the Quit button to access its Click event.

Enter the following code in the Quit button’s Click event handler; press Enter at the end of each statement:

' Close the window and exit the application
Me.Close()

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020