昨天写了个google的feed api应用,突然对rss蛮感兴趣的,天生比较好奇,以前都是做windows程序感觉进入互联网领域,象是走进另外一扇大门,更加有趣,更加丰富多彩.先展示一下结果
调用feed api最主要要学习的知识是RSS读取的问题.
.NET框架提供了System.Xml.Serialization.XmlSerializer类型，为将对象序列化为XML或将XML序列化为对象提供了很大支持。
下面我们针对yahoo weather feed api,通过实例讲解一下如何读取RSS文件。
首先通过yahoo weather feed api
可以得到如下RSS文件
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<channel>
<title>Yahoo! Weather - Hangzhou, CH</title>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/Hangzhou__CH/*http://weather.yahoo.com/forecast/CHXX0044_f.html</link>
<description>Yahoo! Weather for Hangzhou, CH</description>
<language>en-us</language>
<lastBuildDate>Fri, 27 Feb 2009 12:30 pm CST</lastBuildDate>
<ttl>60</ttl>
<yweather:location city="Hangzhou" region="" country="CH" />
<yweather:units temperature="F" distance="mi" pressure="in" speed="mph" />
<yweather:wind chill="39" direction="20" speed="7" />
<yweather:atmosphere humidity="81" visibility="1.86" pressure="30.27" rising="0" />
<yweather:astronomy sunrise="6:28 am" sunset="5:57 pm" />
<image>
<title>Yahoo! Weather</title>
<width>142</width>
<height>18</height>
<link>http://weather.yahoo.com</link>
<url>http://l.yimg.com/a/i/us/nws/th/main_142b.gif</url>
</image>
<item>
<title>Conditions for Hangzhou, CH at 12:30 pm CST</title>
<geo:lat>30.23</geo:lat>
<geo:long>120.17</geo:long>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/Hangzhou__CH/*http://weather.yahoo.com/forecast/CHXX0044_f.html</link>
<pubDate>Fri, 27 Feb 2009 12:30 pm CST</pubDate>
<yweather:condition text="Rain Shower" code="11" temp="43" date="Fri, 27 Feb 2009 12:30 pm CST" />
<description>
<![CDATA[
<br />
<b>Current Conditions:</b>
<br />
Rain Shower, 43 F<BR />
<BR />
<b>Forecast:</b>
<BR />
Fri - Rain. High: 42 Low: 39<br />
Sat - Rain. High: 43 Low: 40<br />
<br />
<BR/>
(provided by The Weather Channel)<br/>
]]>
</description>
<yweather:forecast day="Fri" date="27 Feb 2009" low="39" high="42" text="Rain" code="12" />
<yweather:forecast day="Sat" date="28 Feb 2009" low="40" high="43" text="Rain" code="12" />
<guid isPermaLink="false">CHXX0044_2009_02_27_12_30_CST</guid>
</item>
</channel>
</rss>
<!-- api4.weather.sp1.yahoo.com uncompressed/chunked Thu Feb 26 21:00:04 PST 2009 -->
如上文所说.NET框架提供了System.Xml.Serialization.XmlSerializer类型，现在我们要做的就是如何利用xmlSerializer将XML序列化为对象。
对于上面的XML文件为了便于对象序列化我们会做如下替换
str = str.Replace("yweather:", "")
str = str.Replace("geo:", "")
'Dim str1 As String = """ : "
Dim str1 = "isPermaLink=""false"""
str = str.Replace(str1, "")
str = str.Replace(str1, "")
接着我们需要按照xml的格式，将所有的节点定义为对象，并将节点的属性定义为对象的属性。
如该RSS中需要先定义rss对象
Imports Microsoft.VisualBasic
Imports System.Xml.Serialization
Partial Class YahooWeatherForecast
<XmlRoot("rss")> _
Public Class rssClass
Private _channel As channelClass
<XmlElement()> _
Public Property channel() As channelClass
Get
Return _channel
End Get
Set(ByVal value As channelClass)
_channel = value
End Set
End Property
End Class
End Class
在该对象中包含chanelClass，保持和xml的文件相同的结构
接下来我们需要定义chanelClass,代码如下:
Imports Microsoft.VisualBasic
Imports System.Xml.Serialization
Partial Class YahooWeatherForecast
Partial Class rssClass
Partial Class channelClass
Private _title As String
''' <summary>
''' The title of the feed, which includes the location city. For example "Yahoo! Weather - Sunnyvale, CA"
''' </summary>
<XmlElement()> _
Public Property title() As String
Get
Return _title
End Get
Set(ByVal value As String)
_title = value
End Set
End Property
Private _link As String
''' <summary>
''' </summary>
<XmlElement()> _
Public Property link() As String
Get
Return _link
End Get
Set(ByVal value As String)
_link = value
End Set
End Property
Private _language As String
''' <summary>
''' The language of the weather forecast, for example, en-us for US English.
''' </summary>
<XmlElement()> _
Public Property language() As String
Get
Return _language
End Get
Set(ByVal value As String)
_language = value
End Set
End Property
Private _description As String
''' <summary>
''' The overall description of the feed including the location, for example "Yahoo! Weather for Sunnyvale, CA"
''' </summary>
<XmlElement()> _
Public Property description() As String
Get
Return _description
End Get
Set(ByVal value As String)
_description = value
End Set
End Property
Private _lastBuildDate As String
''' <summary>
''' The last time the feed was updated. The format is in the date format defined by RFC822 Section 5, for example Mon, 256 Sep 17:25:18 -0700.
''' </summary>
<XmlElement()> _
Public Property lastBuildDate() As String
Get
Return _lastBuildDate
End Get
Set(ByVal value As String)
_lastBuildDate = value
End Set
End Property
Private _ttl As String
''' <summary>
''' Time to Live; how long in minutes this feed should be cached.
''' </summary>
<XmlElement()> _
Public Property ttl() As String
Get
Return _ttl
End Get
Set(ByVal value As String)
_ttl = value
End Set
End Property
Private _location As locationClass
''' <summary>
''' The location of this forecast.
''' </summary>
<XmlElement()> _
Public Property location() As locationClass
Get
Return _location
End Get
Set(ByVal value As locationClass)
_location = value
End Set
End Property
Private _units As unitsClass
''' <summary>
''' Units for various aspects of the forecast.
''' </summary>
<XmlElement()> _
Public Property units() As unitsClass
Get
Return _units
End Get
Set(ByVal value As unitsClass)
_units = value
End Set
End Property
Private _wind As windClass
''' <summary>
''' Forecast information about wind.
''' </summary>
<XmlElement()> _
Public Property wind() As windClass
Get
Return _wind
End Get
Set(ByVal value As windClass)
_wind = value
End Set
End Property
Private _atmosphere As atmosphereClass
''' <summary>
''' Forecast information about current atmospheric pressure, humidity, and visibility.
''' </summary>
<XmlElement()> _
Public Property atmosphere() As atmosphereClass
Get
Return _atmosphere
End Get
Set(ByVal value As atmosphereClass)
_atmosphere = value
End Set
End Property
Private _astronomy As astronomyClass
''' <summary>
''' Forecast information about current astronomical conditions.
''' </summary>
<XmlElement()> _
Public Property astronomy() As astronomyClass
Get
Return _astronomy
End Get
Set(ByVal value As astronomyClass)
_astronomy = value
End Set
End Property
Private _image As imageClass
''' <summary>
''' The image used to identify this feed
''' </summary>
<XmlElement()> _
Public Property image() As imageClass
Get
Return _image
End Get
Set(ByVal value As imageClass)
_image = value
End Set
End Property
Private _item As itemClass
''' <summary>
''' The local weather conditions and forecast for a specific location.
''' </summary>
<XmlElement()> _
Public Property item() As itemClass
Get
Return _item
End Get
Set(ByVal value As itemClass)
_item = value
End Set
End Property
End Class
End Class
End Class
在chanel中声明了他包含哪些子节点，同样我们也需要为这些子节点申明对象。
Imports Microsoft.VisualBasic
Imports System.Xml.Serialization
Partial Class YahooWeatherForecast
Partial Class rssClass
Partial Class channelClass
Public Class atmosphereClass
Private _humidity As Integer
''' <summary>
''' humidity, in percent
''' </summary>
<XmlAttribute()> _
Public Property humidity() As Integer
Get
Return _humidity
End Get
Set(ByVal value As Integer)
_humidity = value
End Set
End Property
Private _visibility As Double
''' <summary>
''' in the units specified by the distance attribute of the units element (mi or km). Note that the visibility is specified as the actual value * 100. For example, a visibility of 16.5 miles will be specified as 1650. A visibility of 14 kilometers will appear as 1400.
''' </summary>
<XmlAttribute()> _
Public Property visibility() As Double
Get
Return _visibility
End Get
Set(ByVal value As Double)
_visibility = value
End Set
End Property
Private _pressure As Double
''' <summary>
''' barometric pressure, in the units specified by the pressure attribute of the units element (in or mb).
''' </summary>
<XmlAttribute()> _
Public Property pressure() As Double
Get
Return _pressure
End Get
Set(ByVal value As Double)
_pressure = value
End Set
End Property
Private _rising As Integer
''' <summary>
''' state of the barometric pressure, steady = 0, rising = 1, falling = 2
''' </summary>
<XmlAttribute()> _
Public Property rising() As Integer
Get
Return _rising
End Get
Set(ByVal value As Integer)
_rising = value
End Set
End Property
End Class
End Class
End Class
End Class
在申明完对象之后，我们就可以将xml文件转换为相应的对象。
代码如下：
Dim doc As New System.Xml.XmlDocument()
Dim c As rssClass
'Load data
doc.Load(str)
str = doc.OuterXml
'XmlSerializer could not Serialize XML with this Elements so i just replace them with Null String!
str = str.Replace("yweather:", "")
str = str.Replace("geo:", "")
'Dim str1 As String = """ : "
Dim str1 = "isPermaLink=""false"""
str = str.Replace(str1, "")
str = str.Replace(str1, "")
Dim memoryStream As New IO.MemoryStream()
Dim d As New IO.StringReader(str)
Dim xs As New XmlSerializer(GetType(rssClass))
c = CType(xs.Deserialize(d), rssClass)
rss = c
最后用户可以根据自己的需要将对象中的属性取出，使用于相关的应用中。类似如下代码
Dim t As New YahooWeatherLib.YahooWeatherForecast("CHXX0044", "f")
Label1.Text = t.rss.channel.item.forecast.high
Label2.Text = t.rss.channel.item.forecast.low
Label5.Text = t.rss.channel.item.title
本文转自elbertchen 51CTO博客，原文链接：http://blog.51cto.com/linkyou/282659，如需转载请自行联系原作者
