ARTICLE

Stock Tracker Custom Control

Posted by Scott Lysle in Articles | ASP.NET using VB.NET on November 03, 2006

Tags: ASP.NET 2.0, Custom Web Control Programming, HtmlTextWriter, Visual Basic 2005, Web Programming, Web Services, XML

This article describes the construction of a custom control used to check stock prices as made available through a public web service. The article includes the source code for this custom control and well as a demonstration site used to test the control.

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Download Files:

StockTrackerCode.zip

Reader Level: Beginner

Introduction:

Figure 1: Stock Tracker Custom Controls in Use

Getting Started:

The files included with this project include a web control library project and a demonstration web site. In order to get started, open the included zip file and install the two projects onto your file system. Open IIS and create a virtual directory for the web application. Open the solution into Visual 2005 and make any changes necessary to bring both projects into the solution. Once properly configured, your solution explorer should show these projects, references, and files:

Figure 2: Solution Explorer with Web App and Control Library

In examining the solution, note that the "StockTracker" control library contains only a single control and that control is called "StockDog". This project also includes a web reference that points to the http://www.webservicex.net site; this public site supports the web service used to capture the stock prices.

The web application contains only a single web page (default.aspx) and includes a reference to the "StockTracker" DLL.
The web application serves as a container used to test the custom control; the default.aspx page contains three separate instances of the custom control. Each of these three instances is directed to retrieve stock information from three separate stocks.

The Code: StockDog

The "StockDog" custom control is constructed to retrieve the information from the web service upon initialization and to use that information to populate a collection of local member variables; each of the local member variables is set to contain one of the values collected from the web service.

The web service returns the requested data in the form of an XML string; this string is parsed to obtain the individual values used to populate the member variables. These member variables are in turn used to display the stock information when the page is rendered.

In examining the code, note that, aside from the default imports, only the System.XML class has been added. The class itself inherits from the WebControl class.

Imports System

Imports System.Collections.Generic

Imports System.ComponentModel

Imports System.Text

Imports System.Web

Imports System.Web.UI

Imports System.Web.UI.WebControls

Imports System.Xml

<DefaultProperty("StockTicker"), ToolboxData("<{0}:StockDog runat=server></{0}:StockDog>")> _

Public Class StockDog

Inherits WebControl

Following the class declaration, a region entitled "Declarations" is created and within that region are the declarations for all of the private member variables used within the control.

#Region "Declarations"

Private mStocks As net.webservicex.www.StockQuote

Private mXmlDoc As XmlDocument

Private mStockTicker As String

Private mLast As String

Private mDate As String

Private mTime As String

Private mChange As String

Private mOpen As String

Private mHigh As String

Private mLow As String

Private mVolume As String

Private mMktCap As String

Private mPrevClose As String

Private mPercentChng As String

Private mAnnRange As String

Private mEarns As String

Private mPE As String

Private mName As String

#End Region

After the variable declarations, there is another region defined (Methods) and within that region is the code used to capture the data from the web service, and to read the XML string returned by that service and use the values to populate the member variables. The init handler calls a subroutine called "Fetch" each time the control is initialized. Fetch accepts a single argument in the form of a string bearing the stock symbol (e.g., MSFT for Microsoft).

Inside Fetch, a new XML document is created. The mStocks string variable is used to capture the XML string returned from the web service's GetQuote web method. GetQuote accepts the stock symbol as an argument. The returned string is loaded as XML into the XML document.

After the data is returned and placed inside the XML document, the next windy bit of code locates each specific node and captures the value associated with that node which is in turn used to populate the appropriate local member variable.

The code contained in the Methods region is as follows:

#Region "Methods"

Private Sub StockDog_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init

Fetch(StockTicker)

End Sub

Public Sub Fetch(ByVal strStock As String)

mXmlDoc = New XmlDocument()

mStocks = New net.webservicex.www.StockQuote

Dim strQuote As String = mStocks.GetQuote(strStock)

mXmlDoc.LoadXml(strQuote)

' Set all of the private member variables to

' contain the values from the xml string returned

' from the web service

' Last

Dim lastNodes As XmlNodeList

Dim lastNode As XmlNode

lastNodes = mXmlDoc.GetElementsByTagName("Last")

For Each lastNode In lastNodes

mLast = lastNode.ChildNodes(0).Value

' Date

Dim dateNodes As XmlNodeList

Dim dateNode As XmlNode

dateNodes = mXmlDoc.GetElementsByTagName("Date")

For Each dateNode In dateNodes

mDate = dateNode.ChildNodes(0).Value

' Time

Dim timeNodes As XmlNodeList

Dim timeNode As XmlNode

timeNodes = mXmlDoc.GetElementsByTagName("Time")

For Each timeNode In timeNodes

mTime = timeNode.ChildNodes(0).Value

' Change

Dim changeNodes As XmlNodeList

Dim changeNode As XmlNode

changeNodes = mXmlDoc.GetElementsByTagName("Change")

For Each changeNode In changeNodes

mChange = changeNode.ChildNodes(0).Value

' Open

Dim openNodes As XmlNodeList

Dim openNode As XmlNode

openNodes = mXmlDoc.GetElementsByTagName("Open")

For Each openNode In openNodes

mOpen = openNode.ChildNodes(0).Value

' High

Dim highNodes As XmlNodeList

Dim highNode As XmlNode

highNodes = mXmlDoc.GetElementsByTagName("High")

For Each highNode In highNodes

mHigh = highNode.ChildNodes(0).Value

' Low

Dim lowNodes As XmlNodeList

Dim lowNode As XmlNode

lowNodes = mXmlDoc.GetElementsByTagName("Low")

For Each lowNode In lowNodes

mLow = lowNode.ChildNodes(0).Value

' Volume

Dim volumeNodes As XmlNodeList

Dim volumeNode As XmlNode

volumeNodes = mXmlDoc.GetElementsByTagName("Volume")

For Each volumeNode In volumeNodes

mVolume = volumeNode.ChildNodes(0).Value

' MrkCap

Dim MrkCapNodes As XmlNodeList

Dim MrkCapNode As XmlNode

MrkCapNodes = mXmlDoc.GetElementsByTagName("MktCap")

For Each MrkCapNode In MrkCapNodes

mMktCap = MrkCapNode.ChildNodes(0).Value

' PrevClose

Dim prevCloseNodes As XmlNodeList

Dim prevCloseNode As XmlNode

prevCloseNodes = mXmlDoc.GetElementsByTagName("PreviousClose")

For Each prevCloseNode In prevCloseNodes

mPrevClose = prevCloseNode.ChildNodes(0).Value

' mPercentChng

Dim percentChngNodes As XmlNodeList

Dim percentChngNode As XmlNode

percentChngNodes = mXmlDoc.GetElementsByTagName("PercentageChange")

For Each percentChngNode In percentChngNodes

mPercentChng = percentChngNode.ChildNodes(0).Value

' mAnnRange

Dim annRangeNodes As XmlNodeList

Dim annRangeNode As XmlNode

annRangeNodes = mXmlDoc.GetElementsByTagName("AnnRange")

For Each annRangeNode In annRangeNodes

mAnnRange = annRangeNode.ChildNodes(0).Value

' mEarns

Dim earnsNodes As XmlNodeList

Dim earnsNode As XmlNode

earnsNodes = mXmlDoc.GetElementsByTagName("Earns")

For Each earnsNode In earnsNodes

mEarns = earnsNode.ChildNodes(0).Value

' mPE

Dim PENodes As XmlNodeList

Dim PENode As XmlNode

PENodes = mXmlDoc.GetElementsByTagName("P-E")

For Each PENode In PENodes

mPE = PENode.ChildNodes(0).Value

' mName

Dim nameNodes As XmlNodeList

Dim nameNode As XmlNode

nameNodes = mXmlDoc.GetElementsByTagName("Name")

For Each nameNode In nameNodes

mName = nameNode.ChildNodes(0).Value

End Sub

#End Region

The next region defined in the code is called "Properties"; as you likely guessed, this section contains the properties used by the control. In this case, aside from what was passed down through the inheritance of the WebControl class, the only property to define is a string value used to contain the stock symbol. The properties region and its single property are defined as follows:

#Region "Properties"

<Category("Stock Symbol")> _

<Browsable(True)> _

<Description("Enter the stock ticker value.")> _

Public Property StockTicker() As String

Get

Return mStockTicker

End Get

Set(ByVal value As String)

mStockTicker = value

End Set

End Property

#End Region

The attributes of category, browsable, and description are used to provide design time support for the custom control. The category and description text will be displayed in the IDE's property editor whenever this control is selected by the developer using the control.

Having captured the values from the XML string returned from the web service, and having populated the local member variables using the values contained in the XML, the only remaining step is to render the control. A region entitled, "Rendering" follows and it contains the code necessary to render the control on the page.

The code used to render the control is pretty simple; the HtmlTextWriter is used to define a table and set up its characteristics (cell padding and border in this example), each row of the table contains two cells, a label and its associated value are placed into each of those two cells. Once all of the data has been written into the table, the ending tag is rendered and the control is complete.

Naturally, you can change the configuration of the table or remove some of the data returned from the web service by making changes in the definition of the HTML as defined through the HtmlTextWriter. The RenderContents subroutine is overridden and the HTML is formatted within this subroutine through the use of the HtmlTextWriter.

#Region "Rendering"

Protected Overrides Sub RenderContents(ByVal output As HtmlTextWriter)

output.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "3")

output.AddAttribute(HtmlTextWriterAttribute.Border, "1")

output.RenderBeginTag(HtmlTextWriterTag.Table)

output.RenderBeginTag(HtmlTextWriterTag.Tr)

output.AddAttribute(HtmlTextWriterAttribute.Align, "left")