Unidev Tech Blog

Archive for the ‘C#’ Category

I find myself using .net data containers in many web applications.  Binding controls such as asp:Repeater and asp:DataList to data sources can make displaying your data more manageable.  In a few of those instances I need to have some of the data display in a little different manner depending on that particular info.

For example, a “sold” image could be shown if the status of a data item warrants it.  If the status is anything else no extra HTML is rendered.

<%# (DataBinder.Eval(Container.DataItem, "Status").ToString() == "Sold") ?
<img src='/images/sold.gif' />" : "" %>

Instead of making a server-side control in my .aspx page then having my code behind find it in some sort of databound function, I find it cleaner to use an inline C# IF statement for simple display changes such as these.

In the sample code below, we are making an anchor link. The data in the “Type” column from the database describes if the data is a URL or an email address.  Our inline IF statement has this structure:

If the Type equals “Website” then add nothing to the data.  Otherwise, the data is an email address, so make a “mailto:” link out if it.

<asp:Repeater id="rptAddress" runat="server">
<ItemTemplate>

<a href="<%# (DataBinder.Eval(Container.DataItem, "Type").ToString() == "Website") ?
 "" : "mailto:" %>   <%# DataBinder.Eval(Container.DataItem, "Address")%>" >
<%# DataBinder.Eval(Container.DataItem, "Address")%>
</a>

</ItemTemplate>
</asp:Repeater>

Just remember, the C# syntax for an inline If uses the question mark and a colon:

<% (condition) ? "true" : "false" %>

By George Zheng

XML has been used in a lot of places for transferring data because of its platform independence and its simple, text-based, self-describing format. It is a common requirement for preparing and consuming XML data. Microsoft provides several convenience tools to help developers deal with XML under .NET platform.

1. System.Xml.XmlTextReader/System.Xml.XmlTextWriter
2. System.Xml.Serialization.XMLSerializer
3. System.Xml.Linq

XmlTextReader/XmlTextWriter
XmlDocument objects are easy to use for navigating the DOM copying, modifying, or inserting nodes. However, they can also use a large amount of memory to store the entire DOM of a large XML string in memory. Because of this, the XmlTextReader and XmlTextWriter classes can be used for stream based manipulation of an XML string.
Let’s say you have an XML as:
<?xml version=“1.0“ encoding=“utf-8“ ?>
<user id=“1“>
<firstname>George</firstname>
<lastname>Zheng</lastname>
</user>

Following code will read it into a user object.

User user = new User();
XmlTextReader reader = new XmlTextReader(“user.xml”);

while (reader.Read())
{
if (reader.NodeType == XmlNodeType.Element)
{
if (reader.Name == “user”)
{
user.Id = Convert.ToInt32(reader.GetAttribute(“id”));
}
if (reader.Name == “firstname”)
{
user.Firstname = reader.ReadElementContentAsString();
}
if (reader.Name == “lastname”)
{
user.Lastname = reader.ReadElementContentAsString();
}
}
}
With XmlTextWriter, following code will generate XML string:

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
XmlTextWriter writer = new XmlTextWriter(sw);

writer.WriteStartElement(“user”);
writer.WriteAttributeString(“id”, user.Id.ToString());
writer.WriteElementString(“firstname”, user.Firstname);
writer.WriteElementString(“lastname”, user.Lastname);
writer.WriteEndElement();

return sb.ToString();

XMLSerializer

If you don’t want to deal with the XML element by element, .NET provides an alternative approach to convert object instance to XML and read the data back – XML Serialization. This is more convenience for a complex object.

TextReader tr = new StringReader(xml);
XmlSerializer s = new XmlSerializer(typeof(User));
User user = (User)s.Deserialize(tr);

Following code can be used to serialize the object:

XmlSerializer s = new XmlSerializer(typeof(User));
TextWriter writer = new StringWriter();
s.Serialize(writer, user);
writer.Flush();
string xml = writer.ToString();
writer.Close();

The object can be a complex object like:

public class User
{
[XmlAttribute("id")]
public int Id { get; set; }

[XmlElement("firstname")]
public string Firstname { get; set; }
[XmlElement("lastname")]
public string Lastname { get; set; }

[XmlArray("projects")]
[XmlArrayItem("project", typeof(Project))]
public List<Project> Projects { get; set; }
}

public class Project
{
[XmlAttribute("id")]
public int Id { get; set; }
[XmlElement("name")]
public string Name { get; set; }
}

As you can see, serializer attributes can be used to specify how the object’s properties map to XML entities. I’m not going to discuss these attributes here. Details can be found from Useful Links below.

LINQ

In some case, convert the whole XML may not be a good idea. Linq provides a convenience approach to query a complex XML.

Here is the example account feed response from Google Analytics API

<?xml version=‘1.0‘ encoding=‘UTF-8‘?>
<feed xmlns=‘http://www.w3.org/2005/Atom‘ xmlns:openSearch=‘http://a9.com/-/spec/opensearchrss/1.0/‘ xmlns:dxp=‘http://schemas.google.com/analytics/2009‘>
<id>http://www.google.com/analytics/feeds/accounts/abc@test.com</id>
<updated>2009-06-25T03:55:22.000-07:00</updated>
<title type=‘text‘>Profile list for abc@test.com</title>
<link rel=‘self‘ type=‘application/atom+xml‘ href=‘http://www.google.com/analytics/feeds/accounts/default‘/>
<author>
<name>Google Analytics</name>
</author>
<generator version=‘1.0‘>Google Analytics</generator>
<openSearch:totalResults>12</openSearch:totalResults>
<openSearch:startIndex>1</openSearch:startIndex>
<openSearch:itemsPerPage>12</openSearch:itemsPerPage>
<entry>
<id>http://www.google.com/analytics/feeds/accounts/ga:1174</id>
<updated>2009-06-25T03:55:22.000-07:00</updated>
<title type=‘text‘>www.googlestore.com</title>
<link rel=‘alternate‘ type=‘text/html‘ href=‘http://www.google.com/analytics‘/>
<dxp:tableId>ga:1174</dxp:tableId>
<dxp:property name=‘ga:accountId‘ value=‘30481‘/>
<dxp:property name=‘ga:accountName‘ value=‘Google Store‘/>
<dxp:property name=‘ga:profileId‘ value=‘1174‘/>
<dxp:property name=‘ga:webPropertyId‘ value=‘UA-30481-1‘/>
<dxp:property name=‘ga:currency‘ value=‘USD‘/>
<dxp:property name=‘ga:timezone‘ value=‘America/Los_Angeles‘/>
</entry>
<entry>
<id>http://www.google.com/analytics/feeds/accounts/ga:6284812</id>
<updated>2009-01-06T17:39:33.000-08:00</updated>
<title type=‘text‘>www.googlestore.com (Test Team)</title>
<link rel=‘alternate‘ type=‘text/html‘ href=‘http://www.google.com/analytics‘/>
<dxp:tableId>ga:6284812</dxp:tableId>
<dxp:property name=‘ga:accountId‘ value=‘30481‘/>
<dxp:property name=‘ga:accountName‘ value=‘Google Store‘/>
<dxp:property name=‘ga:profileId‘ value=‘6284812‘/>
<dxp:property name=‘ga:webPropertyId‘ value=‘UA-30481-1‘/>
<dxp:property name=‘ga:currency‘ value=‘USD‘/>
<dxp:property name=‘ga:timezone‘ value=‘America/Los_Angeles‘/>
</entry>
</feed>

With following code, you will get ID, Title and AccountName for each entry.

XDocument doc = XDocument.Parse(xml);
XNamespace dxpSpace = doc.Root.GetNamespaceOfPrefix(“dxp”);
XNamespace defaultSpace = doc.Root.GetDefaultNamespace();

IEnumerable<Account> entries =
from en in doc.Root.Descendants(defaultSpace + “entry”)
select new Account
{
ID = en.Element(defaultSpace + “id”).Value,
Title = en.Element(defaultSpace + “title”).Value,
AccountName =
en.Elements(dxpSpace + “property”).Where(
xe => xe.Attribute(“name”).Value == “ga:accountName”).First().
Attribute(“value”).Value
};

Useful Links

Insert XML Nodes Using XmlTextReader and XmlTextWriter
Using the XmlSerializer Attributes
Added Google Analytics Reader for .NET


Download source code

 By Allan Sieker

If you want to learn something from one of the best, please check out Clint Edmonson’s web site where you can download free coding standards for both VB and C#.  I worked with Clint at AB and I must say that he is one sharp guy.  I am sure he raised Microsoft’s collective talent a few notches when he joined them.  Be sure to look him up at the St. Louis “Day of .NET” Conference in August.

Shifting gears from .NET to SQL….

I ran across “Ten Common Database Design Mistakes” and found it to be most interesting.  I’m sure you will too.

Usually a website owner has the data from their contact forms emailed to them.  But sometimes it can be useful for the site to automatically add that info to an ongoing list of contacts.  One way that most people like to be able to see and sort such data is in a spreadsheet.  It is quite easy to make a “fake” spreadsheet using an html table that Excel will open like any other .xls file.

Here are the basic steps:

• Create and save a “spreadsheet” which defines the header row
• Upon each contact form submittal, write an html row to that file 

Read the rest of this entry »

by George Zheng

Problem

AJAX Control Toolkit has a neat control – TabContainer, to allow you create tabs on your web page easily. However, one problem with it is that when user refreshes the page, it defaults back to the first tab. This will cause user confusion if you have pagination in third tab let’s say. Every time, when user click a page number on third tab. Page get refreshed and it should show third tab, not the first tab.

Solution

The reason refreshed page always show the first tab is, in fact, one of the benefits of the tab control – switching between tabs doesn’t cause a post back. This is a pure client activity. When server prepares the page, it has no idea which tab is the active tab on client side. So server will set first tab as active tab by default.
Read the rest of this entry »