microsoft visual basic 2008 step by step phần 9 ppsx

You’ll get started by using the Data Source Conﬁ guration Wizard to establish a connection to a database named Students.mdb that I created in Access 2002/2003 format.. Chapter 18 Getting

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428 Part III Designing the User Interface

The PrintPreviewDialog control displays a custom Print Preview dialog box.

The PageSetupDialog control displays a custom Page Setup dialog box.

As with other dialog boxes, you can add these printing controls to your form by using the Toolbox, or you can create them programmatically

In the following exercise, you’ll add Print Preview and Page Setup dialog boxes to the Print File program you’ve been working with In the completed practice ﬁ les, I’ve named this project Print Dialogs so that you can distinguish the code of the two projects, but you can add the dialog box features directly to the Print File project if you want

Add PrintPreviewDialog and PageSetupDialog controls

1 If you didn’t complete the previous exercise, open the Print File project from the

c:\vb08sbs\chap17\print ﬁ le folder

The Print File project is the starting point for this project

2 Display the form, and then use the Button control to add two additional buttons to the

top of the form

3 Double-click the PrintPreviewDialog control on the Printing tab of the Toolbox.

A print preview dialog object is added to the component tray

4 Double-click the PageSetupDialog control on the Printing tab of the Toolbox.

A page setup dialog object is added to the component tray If the objects in the component tray obscure one another, you can drag them to a better (more visible) location, or you can right-click the component tray and select Line Up Icons

5 Set the following properties for the button objects on the form:

Button1 Name

Enabled Text

btnSetup False

“Page Setup”

Button2 Name

Enabled Text

btnPreview False

“Print Preview”

Your form looks like this:

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Chapter 17 Working with Printers 429

6 Double-click the Page Setup button (btnSetup) to display the btnSetup_Click event

procedure in the Code Editor

7 Type the following program code:

The code for creating a Page Setup dialog box in this program is quite simple because the

PrintPageSettings variable has already been deﬁ ned at the top of the form This variable

holds the current page deﬁ nition information, and when it’s assigned to the PageSettings property of the PageSetupDialog1 object, the ShowDialog method automatically loads a

dialog box that allows the user to modify what the program has selected as the default

page orientation, margins, and so on The Try Catch error handler simply handles any rors that might occur when the ShowDialog method is used.

8 Display the form again, and then double-click the Print Preview button (btnPreview)

to display the btnPreview_Click event procedure.

9 Type the following program code:

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it copies the text in the rich text box object to the StringToPrint variable and opens

the Print Preview dialog box Print Preview automatically uses the page settings data

to display a visual representation of the document as it will be printed—you don’t need to display this information manually

Now you’ll make a slight modiﬁ cation to the program code in the btnOpen_Click event

procedure

10 Scroll up to the btnOpen_Click event procedure in the Code Editor.

This is the procedure that displays the Open dialog box, opens a text ﬁ le, and enables the printing buttons Because you just added the Page Setup and Print Preview buttons, you have to add program code to enable those two printing buttons as well

11 Scroll to the bottom of the event procedure, just before the ﬁ nal Catch code block, and

locate the following program statement:

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Chapter 17 Working with Printers 431 Test the Page Setup and Print Preview features

Tip The complete Print Dialogs program is located in the c:\vb08sbs\chap17\print dialogs folder.

1 Click the Start Debugging button on the toolbar

The program opens, with only the ﬁ rst button object enabled

2 Click the Open button, and then open the longﬁ le.txt ﬁ le in the c:\vb08sbs\chap17 folder

The remaining three button objects are now enabled, as shown here:

3 Click the Page Setup button

Your program displays the Page Setup dialog box, as shown here:

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Page Setup provides numerous useful options, including the ability to change the paper size and source, the orientation of the printing (Portrait or Landscape), and the page margins (Left, Right, Top, and Bottom)

4 Change the Left margin to 2, and then click OK

The left margin will now be 2 inches

5 Click the Print Preview button

Your program displays the Print Preview dialog box, as shown in the following

illustration:

One pageTwo pagesThree pagesFour pagesSix pages

PrintZoom

Page Select box

If you’ve used the Print Preview command in Microsoft Ofﬁ ce Word or Microsoft Ofﬁ ce Excel, you will recognize several of the buttons and preview features in this Print Preview dialog box The Zoom, One Page, Two Pages, Three Pages, Four Pages, Six Pages, and Page Select box controls all work automatically in the dialog box No program code is required to make them operate

6 Click the Four Pages button to display your document four pages at a time

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Chapter 17 Working with Printers 433

7 Click the Maximize button on the Print Preview title bar to make the window full size

8 Click the Zoom arrow, and then click 150%

Your screen looks like this:

9 Click the Zoom button and return the view to Auto

10 Click the Three Pages button, and then click the Up arrow in the Page Select box to

view pages 2 through 4

As you can see, this Print Preview window is quite impressive—and you incorporated it into your program with just a few lines of code!

11 If you want to test printing the entire document again, click the Print button

12 When you’re ﬁ nished experimenting, click the Close button to close the Print Preview

dialog box, and then click the Close button to close the program

You’re done working with printers for now

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Chapter 17 Quick Reference

Make it easier to

refer-ence the printing classes

in your projects

Add the following Imports statement to the top of your form:

Imports System.Drawing.Printing Create a printing event

Create a PrintDocument

object in your project

Double-click the PrintDocument control on the Printing tab of the Toolbox.

or

Include the following variable declaration in your program code:

Dim PrintDoc As New PrintDocument Print graphics from a

printing event handler

Use the Graphics.DrawImage method For example:

ev.Graphics.DrawImage(Image.FromFile _ (TextBox1.Text), ev.Graphics.VisibleClipBounds) Print text from a

printing event handler

Use the Graphics.DrawString method in an event handler For example:

ev.Graphics.DrawString(TextBox1.Text, _ New Font("Arial", 11, FontStyle.Regular), _ Brushes.Black, 120, 120)

Call a printing event

handler

Use the Print method of an object of type PrintDocument For example:

PrintDoc.Print() Print multipage text

documents

Write a handler for the PrintPage event, which receives an argument of the type PrintPageEventArgs Compute the rectangular area on the page for the text, use the MeasureString method to determine how much text will

ﬁ t on the current page, and use the DrawString method to print the text

on the page If additional pages are needed, set the HasMorePages erty to True When all text has been printed, set HasMorePages to False.

prop-Open a text ﬁ le by

using the FileStream

class, and load it into a

Display printing dialog

boxes in your programs

Use the PrintDialog, PrintPreviewDialog, and PageSetupDialog controls on

the Printing tab of the Toolbox.

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Microsoft Visual Basic 2008 Step by Step

435

Part IV

Database and Web Programming

In this part:

Chapter 18, Getting Started with ADO.NET 437

Chapter 19, Data Presentation Using the DataGridView Control 465

Chapter 20, Creating Web Sites and Web Pages by Using

Visual Web Developer and ASP.NET 489

In Part IV, you’ll learn how to work with information stored in databases and Web sites First, you’ll learn about Microsoft ADO.NET, an important paradigm for working with database information, and you’ll learn how to display, modify, and search for database content by using a combination of program code and Windows Forms controls Microsoft Visual Studio 2008 was speciﬁ cally designed to create applications that provide access

to a rich variety of data sources These custom interfaces have traditionally been called

database front ends, meaning that through your Microsoft Visual Basic application, the

user is given a more useful window into database information than simply manipulating raw database records However, a more appropriate description in Visual Studio 2008 is

that you can build datacentric applications, meaning that through your application, the

user is invited to explore the full potential of any number of rich data source connections, whether to local or remote locations, and that the application places this data at the center

of the user‘s computing experience

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437

Chapter 18

Getting Started with ADO.NET

After completing this chapter, you will be able to:

Use the Data Source Conﬁ guration Wizard to establish a connection to a database and build a dataset

Use the Dataset Designer and the Data Sources window to examine dataset members and create bound objects on forms

Create datacentric applications by using dataset and data navigator objects

Use bound TextBox and MaskedTextBox controls to display database information on a

how to use TextBox and MaskedTextBox controls to present database information to your user,

and you’ll learn to write SQL SELECT statements that ﬁ lter datasets (and therefore what your user sees and uses) in interesting ways

Database Programming with ADO.NET

A database is an organized collection of information stored in a ﬁ le You can create powerful

databases by using any of a variety of database products, including Access, Microsoft SQL Server, and Oracle You can also store and transmit database information by using XML, a

ﬁ le format designed for exchanging structured data over the Internet and in other settings.Creating and maintaining databases has become an essential task for all major corporations, government institutions, non-proﬁ t agencies, and most small businesses Rich data resources—for example, customer addresses, manufacturing inventories, account balances, employee records, donor lists, and order histories—have become the lifeblood of the business world

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438 Part IV Database and Web Programming

You can use Visual Studio 2008 to create new databases, but Visual Studio 2008 is primarily designed for displaying, analyzing, and manipulating the information in existing databases ADO.NET, ﬁ rst introduced in Microsoft Visual Studio NET 2002, is still the standard data model for database programming in Visual Studio 2008 ADO.NET has been improved over the years to work with a large number of data access scenarios, and it has been carefully optimized for Internet use For example, it uses the same basic method for accessing local, client-server, and Internet-based data sources, and the internal data format of ADO.NET

data-LINQ is included with Visual Studio 2008 and offers the capability to write object-oriented database queries directly within Visual Basic code Some time after the initial release of Visual Studio 2008, Microsoft also pledges to release the ADO.NET Entity Framework, which introduces a new object model, powerful new features, and tools that will make database applications even freer from hard-coded dependencies on a particular data engine or logical model As database technology and the Internet continue to advance, ADO.NET will continue to evolve, and Visual Basic programmers should be well-positioned

to beneﬁ t

Database Terminology

An underlying theme in the preceding section is that database programmers are often faced with new technologies to decode and master, a reorientation often initiated by the terms “new paradigm” or “new database model” Although continually learning new techniques can be a source of frustration, the rapid pace of change can be explained partially by the relative new-ness of distributed and multiple-tier database application programming in Windows, as well

as technical innovations, security needs, and Web programming challenges that are beyond the control of the Visual Studio development team In this chapter, however, we’ll be starting

at the beginning, and with database programming more than almost any other subject, you really need to be exposed to topics step by step Let’s start by understanding some basic

database terminology

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Chapter 18 Getting Started with ADO.NET 439

A ﬁ eld (also called a column) is a category of information stored in a database Typical ﬁ elds

in a customer database might contain customer names, addresses, phone numbers, and

comments All the information about a particular customer or business is called a record (less commonly called a row) When a database is created, information is entered in a table

of ﬁ elds and records Records correspond to rows in the table, and ﬁ elds correspond to columns, as shown here:

A relational database can consist of multiple linked tables In general, most of the databases

that you connect to from Visual Studio will probably be relational databases that contain multiple tables of data organized around a particular theme

In ADO.NET, various objects are used to retrieve and modify information in a database The following illustration shows an overview of the approach that will be covered in more detail

in this chapter:

Database

Connection Dataset

Table adapter

Data navigation

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First a connection is made, which speciﬁ es connection information about the database and

creates something for other controls and components to bind to Next the Data Sources

Conﬁ guration Wizard creates a dataset, which is a representation of one or more database

tables you plan to work with in your program (You don’t manipulate the actual data, but

rather a copy of it.) The Data Sources Conﬁ guration Wizard also adds an XML schema ﬁ le to your project and associates a table adapter and data navigator with the dataset to handle

retrieving data from the database, posting changes, and moving from one record to the next in the dataset You can then bind information in the dataset to controls on a form by

using the Data Sources window or DataBindings property settings.

Working with an Access Database

In the following sections, you’ll learn how to use the ADO.NET data access technology in Visual Basic 2008 You’ll get started by using the Data Source Conﬁ guration Wizard to establish a connection to a database named Students.mdb that I created in Access 2002/2003 format (Of course, it also works with Access 2007, if you have the latest version of Microsoft’s database software.) Students.mdb contains various tables of academic information that would be useful for a teacher who is tracking student coursework or a school administrator who is scheduling rooms, assigning classes, or building a time schedule You’ll learn how to create a dataset based on a table of information in the Students database, and you’ll display this information on a Windows form When you’ve ﬁ nished, you’ll be able to put these skills

to work in your own database projects

Tip Although the sample in this chapter uses an Access database, you don’t have to have Access installed Visual Studio and ADO.NET include the necessary support to understand the Access fi le format, as well as other formats If you decide to open the database in Access, you’ll fi nd that Students.mdb is in Access 2002/2003 format I have also included the fi le in Access 2000 format (Students_2000format.mdb) so that you can experiment with the sample database in Access even if you have an earlier version.

Establish a connection by using the Data Source Conﬁ guration Wizard

1 Start Visual Studio, and create a new Visual Basic Windows Forms Application project

named My ADO Form.

A new project opens in the IDE

2 On the Data menu, click the Add New Data Source command

The Data Source Conﬁ guration Wizard starts in the development environment, as shown in the illustration on the following page

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The Data Source Connection Wizard is a feature within the Visual Studio 2008 IDE that automatically prepares your Visual Basic program to receive database information The wizard prompts you for the type of database that you will be connecting to (a local

or remote database, Web service, or custom data object that you have created), lishes a connection to the data, and then creates a dataset within the program to hold specifi c database tables and fi elds The end result is that the wizard opens the Data Sources window and fi lls it with a visual representation of each database object that you can use in your program

3 Click the Database icon (if it is not already selected) in the Data Source Conﬁ guration

Wizard, and then click Next

The wizard displays a screen that helps you establish a connection to your database

by building a statement called a connection string A connection string contains the

information that Visual Studio needs to open and extract information from a database

ﬁ le This includes a path name and ﬁ le name, but also potentially sensitive data such

as a username and password For this reason, the connection string is treated carefully within the Data Source Connection Wizard, and you should take care to protect it from unauthorized access as you copy your source ﬁ les from place to place

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4 Click the New Connection button

The ﬁ rst time that you click the New Connection button, the Choose Data Source dialog box opens, prompting you to select the database format that you plan to use If you see the Add Connection dialog box instead of the Choose Data Source dialog box, it simply means that your copy of Visual Studio has already been con-

ﬁ gured to favor a particular database format No problem; simply click the Change button in the Add Connection dialog box, and you’ll see the same thing that ﬁ rst-time wizard users see, except that the title bar reads Change Data Source, as shown

in the following illustration:

The Change/Choose Data Source dialog box is the place where you select your ferred database format, which Visual Studio uses as the default format In this chapter, you’ll select the Access format, but note that you can change the database format to one of the other choices at any time You can also establish more than one database connection—each to a different type of database—within a single project

5 Click Microsoft Access Database File, and then click OK (or Continue)

The Add Connection dialog box opens, as shown in the illustration on the following page

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Now you’ll specify the location and connection settings for your database, so that Visual Studio can build a valid connection string

to this ﬁ le in any way, so a username and password are not necessary with Students.mdb However, if your database requires a username and/or password for use, you can specify

it now in the User Name and Password boxes These values are then included in the connection string

8 Click the Test Connection button

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Visual Studio attempts to open the speciﬁ ed database ﬁ le with the connection string that the wizard has built for you If the database is in a recognized format and the username and password entries (if any) are correct, you see the following message:

9 Click OK to close the message box, and then click OK to close the Add Connection

dialog box

Visual Studio displays the Data Source Conﬁ guration Wizard again

10 Click the plus sign (+) next to the Connection String item in the dialog box to display

your completed connection string

Your wizard page looks similar to the following:

The connection string identiﬁ es a provider (also called a managed provider) named

Microsoft.Jet.OLEDB.4.0, which is an underlying database component that understands how to connect to a database and extract data from it The two most popular providers offered by Visual Studio are Microsoft Jet OLE DB and Microsoft SQL Server, but third-party providers are available for many of the other popular database formats

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11 Click the Next button

The wizard displays an alert message indicating that a new local database has been selected, and you are asked if the database should be copied to your project folders (This message appears only the ﬁ rst time that you make a connection to a local data-base ﬁ le If you are repeating this exercise, you probably won’t see the message.)

12 Click No to avoid making an extra copy of the database at this time

You are not commercially distributing this project; it is only a sample program, and an extra copy is not needed

The Data Source Confi guration Wizard now asks you the following question: “Do you want to save the connection string to the application confi guration fi le?” Saving the connection string is the default selection, and in this example, the recommended string name is “StudentsConnectionString” You usually want to save this string within your application’s default confi guration fi le, because then if the location of your database changes, you can edit the string in your confi guration fi le (which is listed in Solution Explorer), as opposed to tracking down the connection string within your program code and recompiling the application

13 Click Next to save the default connection string

You are now prompted to select the subset of database objects that you want to use for this particular project, as shown in the following dialog box:

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Note Visual Studio allows you to use just part of a database or to combine different databases—useful features when you’re working to build datacentric applications.

The items you select in this dialog box are referred to within the project as database

objects Database objects can include tables of ﬁ elds and records, database views, stored

procedures, functions, and other items unique to your database The collective term for all

the database objects that you select is a dataset In this project, the dataset is assigned the default name StudentsDataSet, which you can adjust in the DataSet Name box.

Tip Note that the dataset you create now only represents the data in your database—if

you add, delete, or modify database records in the dataset, you don’t actually modify the underlying database tables until you issue a command that writes your changes back to

the original database Database programmers call this kind of arrangement a disconnected

data source, meaning that there is a layer of abstraction between the actual database and

your dataset.

14 Click the plus sign (+) next to the Tables node to expand the list of the tables included

in the Students.mdb database

The list of the tables that appears in the wizard includes Assignments, Classes, Departments, and Instructors Each table relates to some aspect of academic scheduling The table we’ll use in this example is Instructors.

15 Click the plus sign (+) next to the Instructors node, and then select the check boxes for

the Instructor and PhoneNumber ﬁ elds.

You’ll add these two ﬁ elds to the StudentsDataSet dataset The wizard page looks

like the illustration shown on the following page

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16 Click Finish to complete and close the Data Source Conﬁ guration Wizard

Visual Studio fi nishes the tasks of adding a database connection to your project and confi guring the dataset with the selected database objects (Depending on how the Visual Studio IDE has been used and confi gured, you might or might not see a Data Sources tab or window now.)

17 Click the Save All button on the Standard toolbar to save your changes Specify the

c:\vb08sbs\chap18 folder as the location

18 If Solution Explorer is not currently visible, open it now to display the major ﬁ les and

components contained in the ADO Form project

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Your screen looks like this:

In addition to the standard Solution Explorer entries for a project, you see a new

ﬁ le named StudentsDataSet.xsd This ﬁ le is an XML schema that describes the tables,

ﬁ elds, data types, and other elements in the dataset that you have just created The

presence of the schema ﬁ le means that you have added a typed dataset to your

project (Typed datasets have a schema fi le associated with them, but un-typed datasets don’t.) Typed datasets are advantageous because they enable the Microsoft IntelliSense feature of the Visual Studio Code Editor, and they give you specifi c infor-mation about the fi elds and tables you’re using

19 Click the schema ﬁ le in Solution Explorer, and then click the View Designer button

You see a visual representation of the tables, ﬁ elds, and data adapter commands

related to your new dataset in a visual tool called the Dataset Designer The Dataset

Designer contains tools for creating components that communicate between your

database and your application—what database programmers call data access layer

components You can create and modify table adapters, table adapter queries, data

tables, data columns, and data relationships with the Dataset Designer You can also use the Dataset Designer to review and set important properties related to objects

in a dataset, such as the length of database ﬁ elds and the data types associated with ﬁ elds

20 Click the Instructor ﬁ eld, and then press F4 to highlight the Properties window.

21 Click the MaxLength property.

Your screen looks similar to the illustration on the following page

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Here the Dataset Designer is shown with an active dataset named StudentsDataSet, and the Properties window shows that the MaxLength property is set to allow for a maximum of 50 characters in the Instructor ﬁ eld Although this length seems sufﬁ cient,

you can adjust this property (and others, too) if you ﬁ nd that the underlying database settings are inadequate for your application

Setting the Dataset Designer aside for a moment, let’s continue building the sample database application in the Data Sources window

The Data Sources Window

The Data Sources window is a useful and timesaving feature of the Visual Studio 2008 IDE Its purpose is to display a visual representation of the datasets that have been confi gured for use within your project, and to help you bind these datasets to controls on the form Remember that a dataset is just a temporary representation of database information in your program, and that each dataset contains only a subset of the tables and fi elds within your entire database fi le; that is, only the items that you selected while using the Data Source Confi guration Wizard The dataset is displayed in a hierarchical (tree) view in the Data

Sources window, with a root node for each of the objects that you selected in the wizard Each time you run the wizard to create a new dataset, a new dataset tree is added to the Data Sources window, giving you potential access to a wide range of data sources and views within a single program

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If you have been following the instructions for selecting ﬁ elds in the Instructors table of

the Students database, you have something interesting to display in the Data Sources window now To prepare for the following exercises and display the Data Sources window, display the form again (click the Form1.vb [Design] tab), and then click the Show Data Sources command on the Data menu (You can also click the Data Sources tab if it is

visible.) When the Data Sources window is open, expand the Instructors table so that

you can see the two ﬁ elds that we selected Your Data Sources window looks like this, with the important features identiﬁ ed:

Selected fields within

Instructors table (only

2 of 4 fields used in this example)

Refresh dataset

Add or remove dataset fields

Edit selected dataset in Designer

Add dataset to project

Instructors table from

Students.mdb database

New StudentDataSet

dataset created using Data Source Configuration Wizard

The easiest way to display the information in a dataset on a form (and therefore for your users) is to drag objects from the Data Sources window to the Windows Forms Designer

(This is the Designer you used in earlier chapters, but I am calling it the Windows Forms

Designer here to distinguish it from the Dataset Designer.)

Chapter 19, “Data Presentation Using the DataGridView Control,” describes how you can

display entire tables of data on a form In the remainder of this chapter, however, you’ll experiment with dragging individual ﬁ elds of data to the Windows Forms Designer to bind controls to select ﬁ elds in the Students database Give it a try now

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Chapter 18 Getting Started with ADO.NET 451 Use the Data Sources window to create database objects on a form

1 In the Data Sources window, click the plus sign (+) next to the Instructors node to display

the available ﬁ elds in StudentsDataSet (If you have not already done so.)

Your Data Sources window looks like the previous illustration In Visual Studio 2008, you can display individual ﬁ elds or an entire table of data by simply dragging the desired database objects onto your form

2 Click the Instructor ﬁ eld, which contains the name of each instructor in the Students

database An arrow appears to the right of the Instructor ﬁ eld in the Data Sources

win-dow If the arrow does not appear, make sure that the Form1.vb [Design] tab is active in the Designer window, and then click Instructor again

3 Click the Instructor arrow.

Clicking this arrow displays a list of options related to how a database ﬁ eld is displayed

on the form when you drag it, as shown in the following illustration

Although I haven’t discussed it yet, most of the controls on the Common Controls tab

of the Toolbox have the built-in ability to display database information In Visual Studio

terminology, these controls are called bound controls when they are connected to

data-ready ﬁ elds in a dataset The list of controls you see now is a group of popular options for displaying string information from a database, but you can add additional controls

to the list (or remove items) by clicking the Customize command In this case, however,

you’ll simply use the TextBox control, the default bound control for string data.

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4 Click TextBox in the list, and then drag the Instructor ﬁ eld to the middle of the form in

the Windows Forms Designer

As you drag the ﬁ eld over the form, a plus sign below the pointer indicates that adding this database object to a form is a valid operation When you release the mouse button, Visual Studio creates a data-ready text box object and places a professional-looking navigation bar at the top of the form The form looks something like this (your Data Sources window might be in a different location):

Visual Studio has actually created two objects for this Instructor ﬁ eld: a descriptive label

object containing the name of the ﬁ eld, and a bound text box object that will display the contents of the ﬁ eld when you run the program Below the form in the component tray, Visual Studio has also created several objects to manage internal aspects of the data access process These objects include:

StudentsDataSet, the dataset you created with the Data Source Conﬁ guration

Wizard to represent ﬁ elds in the Students database

InstructorsBindingSource, an intermediary component that acts as a conduit between the Instructors table and bound objects on the form

InstructorsTableAdapter, an intermediary component that moves data between

StudentsDataSet and tables in the underlying Students database

InstructorsBindingNavigator, which provides navigation services and properties related to the navigation toolbar and the Instructors table

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Readers familiar with Visual Basic 2005 will recognize these components as the same database connectivity features introduced in Visual Studio 2005 (In Visual Studio

2003, however, a data adapter object was required for each database table or query used in a project.)

Now you’ll run the program to see how all of these objects work

5 Click the Start Debugging button on the Standard toolbar

The ADO Form program runs in the IDE The text box object is loaded with the ﬁ rst

Instructor record in the database (Delamarco, Stefan), and a navigation toolbar with

several buttons and controls appears at the top of the form, as shown in the following illustration:

First Instructor record

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6 Click the Move Next button to scroll to the second instructor name in the dataset

The McKay, Yvonne record appears

7 Continue scrolling through the dataset one record at a time As you scroll through the

list of names, notice that the position indicator keeps track of where you are in the list

of records

8 Click the Move First and Move Last buttons to move to the ﬁ rst and last records of the

dataset, respectively

9 Delete the last record from the dataset (Halvorson, Kim) by clicking the Delete button

The record is deleted from the dataset, and the position indicator shows that there are now eight records remaining (Halvorson, Michael has become the last and current record.) Your form looks like this:

As I mentioned earlier, the dataset represents only the subset of tables from the

Students database that have been used in this project—the dataset is a disconnected image of the database, not the database itself Accordingly, the record that you deleted has been deleted only from the dataset that is loaded in memory while the program is running However, to verify that the program is actually working with disconnected data and is not modifying the original database, you’ll stop and restart the program now

10 Click the Close button on the form to end the program

The program terminates, and the IDE returns

11 Click Start Debugging to run the program again

When the program restarts and the form loads, the navigation toolbar shows that the dataset contains nine records, as it did originally In other words, it works as expected

12 Click the Move Last button to view the last record in the dataset

The record for Halvorson, Kim appears again This ﬁ nal instructor name was deleted only from memory and has reappeared because the underlying database still con-tains the name

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13 Click the Close button again to close the program

Congratulations! Without writing any program code, you have built a functioning

database application that displays speciﬁ c information from a database Setting up

a dataset has taken many steps, but the dataset is now ready to be used in many

useful ways in the program Although I selected only one table and two ﬁ elds from the Students database to reduce screen clutter and focus our attention, you will probably want

to select a much wider range of objects from your databases when you build datasets using the Data Source Conﬁ guration Wizard As you can see, it

is not necessary to create bound objects for each dataset item on a form—you can decide which database records you want to use and display

Using Bound Controls to Display Database Information

As I mentioned earlier, Visual Studio can use a variety of the controls in the Visual Studio Toolbox to display database information You can bind controls to datasets by dragging ﬁ elds from the Data Sources window (the easiest method), and you can create controls separately on your forms and bind them to dataset objects at a later time This second option is an important feature, because occasionally you will be adding data sources to a project after the basic user interface has been created The procedure I’ll demonstrate in this section handles that situation, while giving you additional practice with binding data objects to controls within a Visual Basic application You’ll create a masked text box object on your form, conﬁ gure the object to format

database information in a useful way, and then bind the PhoneNumber ﬁ eld in StudentsDataSet

to the object

Bind a masked text box control to a dataset object

1 Display the form in the Windows Forms Designer, and then open the Toolbox, if it is not

already visible

2 Click the MaskedTextBox control on the Common Controls tab, and then create a

masked text box object on the form below the Instructor label and text box.

As you might recall from Chapter 6, “Using Decision Structures,” the MaskedTextBox control is similar to the TextBox control, but it gives you more ability to regulate or

limit the information entered by the user into a program The input format for the

MaskedTextBox control is adjusted by setting the Mask property In this exercise, you’ll

use Mask to prepare the masked text box object to display formatted phone numbers from the PhoneNumber ﬁ eld (By default, phone numbers in the Students database are

stored without the spacing, parentheses, or dashes of North American phone numbers, but you want to see this formatting in your program.)

3 Click the shortcut arrow in the upper-right corner of the masked text box object, and

then click the Set Mask command

Tiêu đề	Designing the User Interface
Trường học	University of Information Technology
Chuyên ngành	Computer Science
Thể loại	Bài tập
Năm xuất bản	2008
Thành phố	Ho Chi Minh City

Định dạng
Số trang	57
Dung lượng	1,57 MB