Beginning Microsoft Visual Basic 2008 phần 9 ppt

Chapter 20: Visual Basic 2008 and XML 703 3. Double - click the New button to create a Click handler. Add the highlighted line to the event handler, and also add the AddNewAddress method: Private Sub btnNew_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnNew.Click AddNewAddress() End Sub Public Function AddNewAddress() As Address ‘ save the current address UpdateCurrentAddress() ‘ create a new address Dim newAddress As Address = AddressBook.AddAddress ‘ update the display CurrentAddressIndex = AddressBook.Items.Count ‘ return the new address Return newAddress End Function 4. Run the project. Click New and a new address record is created. Enter a new address: 5. Close the program and the changes will be saved. Open up AddressBook.xml , and you should see the new address. How It Works This time you have a new Address object added to the XML document. It is contained within the Addresses element, so you know that it is part of the same array. The implementation was very simple — all you had to do was ask AddressBook to create a new address, and then you updated the CurrentAddressIndex property so that it equaled the number of items in the AddressBook . This had the effect of changing the display so that it went to record 2 of 2, ready for editing. However, it is important that, before you actually do this, you save any changes that the user might have made. With this application, you are ensuring that any changes the user makes will always be persisted into the XML file. Whenever the user closes the application, creates a new record, or moves backward or forward in the list, you want to call UpdateCurrentAddress so that any changes are saved: Public Function AddNewAddress() As Address ‘ save the current address UpdateCurrentAddress() After you ’ ve saved any changes, it is safe to create the new record and show the new record to the user: ‘ create a new address Dim newAddress As Address = AddressBook.AddAddress ‘ update the display CurrentAddressIndex = AddressBook.Items.Count ‘ return the new address Return newAddress End Function c20.indd 703c20.indd 703 4/1/08 6:42:04 PM4/1/08 6:42:04 PM Chapter 20: Visual Basic 2008 and XML 704 Navigating Addresses Now that you can add new addresses to the address book, you need to wire up the Next and Previous buttons so that you can move through the list. In this Try It Out, you ’ ll be adding the code that reads the next or previous address from the array of addresses maintained by the AddressBook class. Before reading the next or previous address, however, you ’ ll also want to ensure that any changes made to the current address are updated, and you ’ ll be calling the appropriate procedures to update the current address before navigating to a new address. Try It Out Navigating Addresses 1. Open the Form Designer for Form1. Double - click the Next button to create a new Click handler. Add this code and the associated MoveNext method: Private Sub btnNext_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnNext.Click MoveNext() End Sub Public Sub MoveNext() ‘ get the next index Dim newIndex As Integer = CurrentAddressIndex + 1 If newIndex > AddressBook.Items.Count Then newIndex = 1 End If ‘ save any changes UpdateCurrentAddress() ‘ move the record CurrentAddressIndex = newIndex End Sub 2. Next, flip back to the Form Designer and double - click the Previous button. Add the highlighted code: Private Sub btnPrevious_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnPrevious.Click MovePrevious() End Sub Public Sub MovePrevious() ‘ get the previous index Dim newIndex As Integer = CurrentAddressIndex - 1 If newIndex = 0 Then newIndex = AddressBook.Items.Count End If ‘ save changes UpdateCurrentAddress() ‘ move the record CurrentAddressIndex = newIndex End Sub 3. Run the project. You should now be able to move between addresses. c20.indd 704c20.indd 704 4/1/08 6:42:05 PM4/1/08 6:42:05 PM Chapter 20: Visual Basic 2008 and XML 705 How It Works All you ’ ve done here is wire up the buttons so that each one changes the current index. By incrementing the current index, you move forward in the list. By decrementing it, you move backward. However, it ’ s very important that you don ’ t move outside the bounds of the list (in other words, try to move to a position before the first record or to a position after the last record), which is why you check the value and adjust it as appropriate. When you move forward ( MoveNext ), you flip to the beginning of the list if you go off the end. When you move backward ( MovePrevious ), you flip to the end if you go off the start. In both cases, you make sure that before you actually change the CurrentAddressIndex property, you call UpdateCurrentAddress to save any changes: Public Sub MoveNext() ‘ get the next index Dim newIndex As Integer = CurrentAddressIndex + 1 If newIndex > AddressBook.Items.Count Then newIndex = 1 End If ‘ save any changes UpdateCurrentAddress() ‘ move the record CurrentAddressIndex = newIndex End Sub Deleting Addresses To finish the functionality of your address book, you ’ ll deal with deleting items. When deleting items, you must take into account that the item you are deleting is the last remaining item. In this case, you have to provide the appropriate code to add a new blank address. This Try It Out provides this and all necessary functionality to delete an address properly. Try It Out Deleting Addresses 1. Go back to the Form Designer for Form1 and double - click the Delete button. Add this code to the event handler, and also add the DeleteAddress method: Private Sub btnDelete_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnDelete.Click ‘ ask the user if they are ok with this? If MsgBox (“Are you sure you want to delete this address?”, _ MsgBoxStyle.Question Or MsgBoxStyle.YesNo) = _ MsgBoxResult.Yes Then DeleteAddress(CurrentAddressIndex) End If End Sub c20.indd 705c20.indd 705 4/1/08 6:42:05 PM4/1/08 6:42:05 PM Chapter 20: Visual Basic 2008 and XML 706 ‘ DeleteAddress - delete an address from the list Public Sub DeleteAddress(ByVal index As Integer) ‘ delete the item from the list AddressBook.Items.RemoveAt(index - 1) ‘ was that the last address? If AddressBook.Items.Count = 0 Then ‘ add a new address? AddressBook.AddAddress() Else ‘ make sure you have something to show If index > AddressBook.Items.Count Then index = AddressBook.Items.Count End If End If ‘ display the record CurrentAddressIndex = index End Sub 2. Run the project. You should be able to delete records from the address book. Note that if you delete the last record, a new record is automatically created. How It Works The algorithm you ’ ve used here to delete the records is an example of how to solve another classic programming problem. Your application is set up so that it always has to display a record. That ’ s why, when the program is first run and there is no AddressBook.xml , you automatically create a new record. Likewise, when an item is deleted from the address book, you have to find something to present to the user. To physically delete an address from the disk, you use the RemoveAt method on the ArrayList that holds the Address objects. ‘ DeleteAddress - delete an address from the list Public Sub DeleteAddress(ByVal index As Integer) ‘ delete the item from the list AddressBook.Items.RemoveAt(index - 1) Again, notice here that, because you ’ re working with a zero - based array, when you ask to delete the address with an index of 3, you actually have to delete the address at position 2 in the array. The problems start after you ’ ve done that. It could be that you ’ ve deleted the one remaining address in the book. In this case, because you always have to display an address, you create a new one: ‘ was that the last address? If AddressBook.Items.Count = 0 Then ‘ add a new address? AddressBook.AddAddress() Alternatively, if there are items in the address book, you have to change the display. In some cases, the value that ’ s currently stored in CurrentAddressIndex will be valid. For example, if you had five records and are looking at the third one, _currentAddressIndex will be 3. If you delete that record, you have four records, but the third one as reported by _currentAddressIndex is still 3 and is still valid. However, as 4 has now shuffled into 3 ’ s place, you need to update the display. c20.indd 706c20.indd 706 4/1/08 6:42:05 PM4/1/08 6:42:05 PM Chapter 20: Visual Basic 2008 and XML 707 It could be the case that you ’ ve deleted the last item in the list. When this happens, the index isn ’ t valid, because the index would be positioned over the end of the list. (Suppose you have four items in the list; delete the fourth one, and you only have three, but _currentAddressIndex would be 4, which isn ’ t valid.) So, when the last item is deleted, the index will be over the end of the list, so you set it to be the last item in the list: Else ‘ make sure you have something to show If index > AddressBook.Items.Count Then index = AddressBook.Items.Count End If End If Whatever actually happens, you still need to update the display. As you know, the CurrentAddressIndex property can do this for you: ‘ display the record CurrentAddressIndex = index End Sub Testing at the Edges This brings us to a programming technique that can greatly help you test your applications. When writing software, things usually go wrong at the edge. For example, you have a function that takes an integer value, but in order for the method to work properly, the value supplied must lie between 0 and 99. When your algorithm works properly when you give it a valid value, test some values at the boundaries of the valid data. For example: – 1, 0, 99, and 100. In most cases, if your method works properly for one or two of the possible valid values, it works properly for the entire set of valid values. Testing a few values at the edge shows you where potential problems with the method lie. A classic example of this is with your MoveNext and MovePrevious methods. If you had a hundred addresses in your address book and tested only that MoveNext and MovePrevious worked between numbers 10 and 20, it most likely would have worked between 1 and 100. However, the moment you move past 100 (in other words “ go over the edge ” ), problems can occur. If you hadn ’ t handled this case properly by flipping back to 1, your program would have crashed. Integrating with the Address Book Application So far, you ’ ve built an application that is able to save and load its data as an XML document. You ’ ve also taken a look at the document as it ’ s been changing over the course of the chapter, so by now you should have a pretty good idea of what an XML document looks like and how it works. c20.indd 707c20.indd 707 4/1/08 6:42:06 PM4/1/08 6:42:06 PM Chapter 20: Visual Basic 2008 and XML 708 The beginning of this chapter pitched XML as a technology for integrating software applications. It then went on to say that for newcomers to Visual Basic, using XML for integration is unlikely to be something that you would do on a day - to - day basis, and so you ’ ve been using XML to store data. In the rest of this chapter, we ’ re going to demonstrate why XML is such a good technology for integration. What you ’ ll do is build a separate application that, with very little work, is able to read in and understand the proprietary data format that you ’ ve used in AddressBook.xml . Using XML is an advanced topic, so, if you would like to learn more about the technology and its application, try the following books: Beginning XML, 2nd Edition (ISBN 1 - 86100 - 559 - 8) Visual Basic .NET and XML: Harness the Power of XML in VB.NET Applications (ISBN 0 - 471 - 26509 - 8) Demonstrating the Principle of Integration Before you build the application that can integrate with your address book application, you should try to understand the principles involved. Basically, XML documents are good for integration because they can be easily read, understood, and changed by other people. Old - school file formats require detailed documentation to understand and often don ’ t evolve well — that is, when new versions of the format are released, software that worked with the old formats often breaks. XML documents are typically easily understood. Imagine you ’ d never seen or heard of your address book before, and look at this XML document: < Addresses > < Address > < FirstName > Bryan < /FirstName > < LastName > Newsome < /LastName > < CompanyName > Wiley < /CompanyName > < Address1 > 123 Main St < /Address1 > < Address2 / > < City > Big City < /City > < Region > SE < /Region > < PostalCode > 28222 < /PostalCode > < Country > USA < /Country > < Email > Bryan@email.com < /Email > < /Address > < /Addresses > Common sense tells you what this document represents. You can also perceive how the program that generated it uses it. In addition, you can use the various tools in .NET to load, manipulate, and work with this document. To an extent, you still need to work with the people that designed the structure of the document, especially when more esoteric elements come into play, but you can use this document to some meaningful effect without too much stress. Provided that you know what structure the document takes, you can build your own document or add new things to it. For example, if you know that the Addresses element contains a list of Address elements, and that each Address element contains a bunch of elements that describe the address, you can add your own Address element using your own application. ❑ ❑ c20.indd 708c20.indd 708 4/1/08 6:42:06 PM4/1/08 6:42:06 PM Chapter 20: Visual Basic 2008 and XML 709 To see this happening, you can open the AddressBook.xml file in Notepad. You need to copy the last Address element (complete with the contents) to the bottom of the document, but make sure it remains inside the Addresses element. Change the address data to something else. Here ’ s mine: < ?xml version=”1.0” encoding=”utf-8”? > < AddressBook xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:xsd=”http://www.w3.org/2001/XMLSchema” > < Addresses > < Address > < FirstName > Bryan < /FirstName > < LastName > Newsome < /LastName > < CompanyName > Wiley < /CompanyName > < Address1 > 123 Main St < /Address1 > < Address2 / > < City > Big City < /City > < Region > SE < /Region > < PostalCode > 28222 < /PostalCode > < Country > USA < /Country > < Email > Bryan@email.com < /Email > < /Address > < Address > < FirstName > Jennifer < /FirstName > < LastName > Newsome < /LastName > < CompanyName / > < Address1 > 123 Main St < /Address1 > < Address2 / > < City > Big City < /City > < Region > SE < /Region > < PostalCode > 28222 < /PostalCode > < Country > USA < /Country > < Email / > < /Address > < /Addresses > < /AddressBook > Finally, if you save the file and run the address book application, you should find that you have two addresses and that the last one is the new one that you added. What this shows is that you can manipulate the document and gain some level of integration. Reading the Address Book from Another Application To further the illustration, what you do in the next Try It Out is build a completely separate application from Address Book that ’ s able to load in the XML file that Address Book uses and do something useful with it. Specifically, you ’ ll extract all of the addresses in the file and display a list of names with their matching e - mail addresses. c20.indd 709c20.indd 709 4/1/08 6:42:06 PM4/1/08 6:42:06 PM Chapter 20: Visual Basic 2008 and XML 710 Try It Out Reading Address Book Data 1. Create a new Windows Forms Application project. Call it Address List . 2. On Form1, draw a ListBox control. Change its IntegralHeight property to False, its Dock property to Fill, and its Name to lstEmails , as shown in Figure 20 - 7 . Figure 20-7 3. Double - click the form ’ s title bar. Add this code to the Load event handler. Remember to add a reference to System.Xml.dll this namespace declaration: Imports System.Xml Public Class Form1 Private Sub Form1_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load ‘ where do we want to get the XML from Dim filename As String = _ “C:\Users\Bryan\Documents\Visual Studio 2008\Projects\Address _ Book\bin\Debug\AddressBook.xml” ‘ open the document Dim reader As New XmlTextReader(filename) ‘ move to the start of the document reader.MoveToContent() ‘ start working through the document Dim addressData As Collection = Nothing Dim elementName As String = Nothing Do While reader.Read ‘ what kind of node to we have? Select Case reader.NodeType ‘ is it the start of an element? Case XmlNodeType.Element ‘ if it’s an element start, is it “Address”? If reader.Name = “Address” Then ‘ if so, create a new collection addressData = New Collection() Else ‘ if not, record the name of the element elementName = reader.Name c20.indd 710c20.indd 710 4/1/08 6:42:07 PM4/1/08 6:42:07 PM Chapter 20: Visual Basic 2008 and XML 711 End If ‘ if we have some text, try storing it in the ‘ collection Case XmlNodeType.Text ‘ do we have an address? If Not addressData Is Nothing Then addressData.Add(reader.Value, elementName) End If ‘ is it the end of an element? Case XmlNodeType.EndElement ‘ if it is, we should have an entire address stored If reader.Name = “Address” Then ‘ try to create a new listview item Dim item As String = Nothing Try item = addressData(“firstname”) & _ “ “ & addressData(“lastname”) item & = “ (“ & addressData(“email”) & “)” Catch End Try ‘ add the item to the list lstEmails.Items.Add(item) ‘ reset addressData = Nothing End If End Select Loop End Sub End Class We ’ ve assumed in this code listing that your AddressBook.xml will be in C:\Users\Bryan\ Documents\Visual Studio 2008\Projects\Address Book\bin\Debug . If yours isn ’ t, change the file name value specified at the top of the code. 4. Run the project; you should see something like what is shown in Figure 20 - 8 . Notice that addresses that don ’ t have an e - mail address display without problems, as the Email element in your XML file contains an empty string value instead of a null value as is typically found in databases. Figure 20-8 c20.indd 711c20.indd 711 4/1/08 6:42:07 PM4/1/08 6:42:07 PM Chapter 20: Visual Basic 2008 and XML 712 How It Works To fully appreciate the benefit of this exercise (and therefore the benefit of XML), imagine that before writing the application you ’ d never seen the XML format used by the Address Book application. Since XML is a text - based format, you ’ re able to open it in a normal text editor, read it, and make assumptions about how it works. You know that you want to get a list of names and e - mail addresses, and you understand that you have an array of Address elements, each one containing the three elements you need: FirstName , LastName , and Email . All that remains is to extract and present the information. Since announcing .NET, Microsoft has a made a big deal about how it is built on XML. This shows in the .NET Framework support for XML — there is a dazzling array of classes for reading and writing XML documents. The XmlSerializer object that you ’ ve been using up until now is by far the easiest one to use, but it relies on your having classes that match the document structure exactly. Therefore, if you are given a document from a business partner, you won ’ t have a set of classes that matches the document. As a result, you need some other way to read the document and fit it into whatever classes you do have. In your Address List project, you don ’ t have applicable AddressBook or Address classes, so you had to use some classes to step through a file. The one you ’ re using is System.Xml.XmlTextReader . This class provides a pointer that starts at the top of the document and, on command, moves to the next part of the document. (Each of these parts is called a node .) The pointer will stop at anything, and this includes start tags, end tags, data values, and whitespace. So, when you start, the first thing XmlTextReader tells you about is this node: < ?xml version=”1.0” encoding=”utf-8”? > When you ask it to move on, it tells you about this node: < AddressBook xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:xsd=”http://www.w3.org/2001/XMLSchema” > Then, when you ask it to move on again, it tells you about this node: < Addresses > Then it tells you about < Address > , < FirstName > , - Bryan , < /FirstName > , and < LastName > , and so on until it gets to the end of the document. In between each one of these, you may or may not get told about whitespace nodes. By and large, you can ignore these. What your algorithm has to do, then, is get hold of an XmlTextReader and start moving through the document one piece at a time. When you first start, the pointer is set ahead of the first node in the document. Each call to Read moves the pointer along one node, so the first call to Read that you see at the start of the Do . . . While loop actually sets the pointer to the first node: Private Sub Form1_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load ‘ where do you want to get the XML from Dim filename As String = _ “C:\Documents and Settings\Administrator\My Documents\” & _ “Visual Studio\Projects\Address Book\Address Book\bin\Debug\” & _ c20.indd 712c20.indd 712 4/1/08 6:42:07 PM4/1/08 6:42:07 PM [...]... FTP XML is based on building up a document constructed of tags and data 714 c20.indd 714 4/1/08 6:42:08 PM Chapter 20: Visual Basic 2008 and XML XML is primarily used for integration work to make the tasks of data transportation and exchange easier, and you, as a newcomer to Visual Basic and programming in general, are unlikely to do integration work (as it’s typically done by developers with lots of... document To detect when you get to the tag, you need to look for EndElement nodes: ‘ is it the end of an element? Case XmlNodeType.EndElement 713 c20.indd 713 4/1/08 6:42:08 PM Chapter 20: Visual Basic 2008 and XML When you get one of these, if Name is equal to Address, you know that you have reached , and this means that addressData should be fully populated You form a string and add...Chapter 20: Visual Basic 2008 and XML “AddressBook.xml” ‘ open the document Dim reader As New XmlTextReader(filename) ‘ move to the start of the document reader.MoveToContent() ‘ start working through the document Dim... services with Visual Studio 2008 is a breeze In this section, you build a simple web service and are introduced to some of the concepts involved Specifically, you see how to include the appropriate attributes to expose a method as a web service method You also learn how to test your web methods using the test harness built into web services A Web Services Demonstration A web service is basically a class... to test the web service from within Internet Explorer 721 c21.indd 721 4/2/08 5:35:23 PM Chapter 21: Distributed Computing with WCF Try It Out A Demonstration Web Service 1 Open Visual Studio and select File 2 Make sure Visual Basic is selected in the Language box, and File System in the Location box, and select ASP.NET Web Service from the upper list Enter the name as DemoService and click OK (see Figure... the HelloWorld method (You can use another browser to test the service, but Visual Studio 2008 chooses Internet Explorer by default.) These pages are known as the test interface Methods on the class that you want exposed to the web service must be marked with the WebMethod attribute You can see this attribute defined at the beginning of the method (note that it must be encased in a fashion similar to... xmlns=”http://tempuri.org/”>1.414213562373 095 2 How It Works If you look in the SOAP message that was returned, you’ll find a double value that’s as close as you can get to the square root of 2 1.414213562373 095 2 So you know that the method works You should have also seen by now that building simple web services is not hard This is Microsoft s... WebHttpBinding(), “Web”) epSquareRoot.Behaviors.Add(New WebHttpBehavior()) shSquareRoot.AddServiceEndpoint(GetType(ISquareRoot), _ New BasicHttpBinding(), “Soap”) Try shSquareRoot.Open() SoapChannel() HttpChannel() Console.WriteLine(“Done Press any key to exit and close the host”) 7 29 c21.indd 7 29 4/2/08 5:35:26 PM Chapter 21: Distributed Computing with WCF Console.ReadLine() shSquareRoot.Close() Catch ex As Exception... service, and a web service project (or site) can contain many different services 3 If the service.vb page is not open, use the Solution Explorer to open it It is located in the App_Code folder When Visual Studio 2008 created the page, it put an example method on the service called HelloWorld The code looks like the code shown here: _ Public Function HelloWorld() As String Return “Hello World”... computers to use, they’ve been built on the same technology that made the World Wide Web so popular — specifically, the Hypertext Transfer Protocol (HTTP) standard that powers all web servers 7 19 c21.indd 7 19 4/2/08 5:35:22 PM Chapter 21: Distributed Computing with WCF When you’re dealing with web sites for people to read, the client (browser) and server usually exchange a mixture of documents HTML . PM Chapter 20: Visual Basic 2008 and XML 708 The beginning of this chapter pitched XML as a technology for integrating software applications. It then went on to say that for newcomers to Visual Basic, . following books: Beginning XML, 2nd Edition (ISBN 1 - 86100 - 5 59 - 8) Visual Basic .NET and XML: Harness the Power of XML in VB.NET Applications (ISBN 0 - 471 - 265 09 - 8) Demonstrating. names with their matching e - mail addresses. c20.indd 709c20.indd 7 09 4/1/08 6:42:06 PM4/1/08 6:42:06 PM Chapter 20: Visual Basic 2008 and XML 710 Try It Out Reading Address Book Data 1.