编程语言：学习TDC

热点排行

学习TDC

类别：编程语言点击：0 评论：0 推荐：

Using The Tabular Data Control in Internet Explorer

By Premshree Pillai
March 17th 2003
Reader Rating: 8.5

In Web pages, it's possible to create instances of objects that can be used to perform various tasks, using 'ActiveX controls' and 'Java Applets'. These objects are inserted into the Web page using the <OBJECT> HTML tag. Each object has a 32-bit unique identifier that is inserted in the CLASSID attribute of the <OBJECT> tag.

Tabular Data Control

The "Tabular Data Control" is a Microsoft ActiveX control that's built into Microsoft Internet Explorer. Using this object, it is possible to extract ordered (delimited) contents from an ASCII (normally we use the .txt extension) file into HTML elements.

For example, if we have a text file that contains 3 fields (synonymous with columns in a database), and these fields are delimited by a character, then it is possible to extract the values of the fields into an HTML page.

This object is very useful if we have relatively small amounts of data, we need to update this data frequently, and we require client-side scripting. In this situation, the control can act like a small database.

The tabular data control is available in Internet Explorer 4 upwards. The only disadvantage of this control is that, it being an ActiveX control, only Internet Explorer supports it (Netscape requires a plug-in).

Implementation

The ActiveX control is initialized using the <OBJECT> tag. The CLASSID (unique identifier) for the tabular data control is:

CLSID:333C7BC4-460F-11D0-BC04-0080C7055A83

Thus we initialize this control in a Web page as follows:

Any object, like an applet, has a number of parameters, which are specified using the <PARAM> tag. The tabular data control has around 7 parameters, but here, I'll discuss only the more important of these:

·DataURL - The path of the file that contains the data, for e.g. "data.txt".

·UseHeader - When set to true, it indicates that we want to use the field names to reference a particular field. Normally we set it to true, but in some applications the field names (headers) may not be required. The default value is false.

·TextQualifier - The character at the beginning and end of a string of text that qualifies that text. For e.g., Here, ~My name is Premshree~, the TextQualifier is '~'.

·FieldDelim - The Field Delimiter is used to distinguish between the different data fields of the data file. For example, consider a data file where we have the fields name, age and sex. The values for these fields will be written as *SomeName*|*SomeAge*|*SomeSex*. Here, the field delimiter used is '|', and I've used '*' as the text qualifier.

Thus, the complete initialization will look like this:

The parameter names are not case sensitive.

The TextQualifier and FieldDelim parameters can be any character. Choose a character that you're less likely to use in your text.

Examples

In these examples, I will use the text qualifier as "~" and field delimiter as "|". I use the .txt extension for the data files, but you can use any extension you like.

First, let us consider a simple example where I store my name and age in the text file data1.txt. Now, I will display my name and age using the <SPAN> tag. This is how it's done:

name|age
~Premshree Pillai~|~19~

Now, I will extract this data and display it in the Web page, data1.htm, as follows:

The output will display: Premshree 19

Note the attributes wthe SPAN tags. DATASRC specifies the data source to use, which is same as the ID of the object we have initialized (here, 'data1'). The DATAFLD attribute specifies the field of the data we want to display. The data file data1.txt had two fields 'name' and 'age' as you can see. Specifying the DATAFLD as 'name' will display the name.

Note that using the method above, you can extract data from a text file into any HTML element; but the above method is inefficient in that if our data file contains more than 1 entry, we won't be able to extract all the values directly.

In these cases we use the <TABLE> tag. The TABLE tag has a special property, as we'll see in the following example.

Consider a simple example where we store the name, age and sex of 3 persons in a text file. Now, we want to extract this data and display it on the Web page in a tabular form.

The text file, data2.txt looks like this:

name|age|sex
~Premshree Pillai~|~19~|~male~
~Vinod~|~18~|~male~
~Usha~|~19~|~female~

Now, we can extract all the above data and display it in (via data2.htm) a tabular form as follows:

The output will look like this :

Thus, we have specified the three data fields (DATAFLD) in 3 different <TD> tags (columns) only once. The Web page automatically displays all the 3 sets of values (3 rows).

We can add as much content as we want to the text file, and we need not make any modifications to the HTML code that extracts these values.

It is possible to manipulate the tabular data control object using JavaScript. In the first example, the <SPAN> element displayed the first entry of the data file. Now, suppose we add another entry to the file; the data file (data1.txt) now looks like this:

name|age
~Premshree Pillai~|~19~
~Vinod~|~18~

Now, if we want to see the second entry (i.e. Vinod 18), we can do it like this:

<OBJECT ID="data1" CLASSID="CLSID:333C7BC4-460F-11D0-
BC04-0080C7055A83">
<PARAM NAME="DataURL" VALUE="data1.txt">
<PARAM NAME="UseHeader" VALUE="TRUE">
<PARAM NAME="TextQualifier" VALUE="~">
<PARAM NAME="FieldDelim" VALUE="|">
</OBJECT>

<SCRIPT LANGUAGE="JavaScript">
/* Get the complete data record set */
var dataSet=data1.recordset;

/* Go to next data */
dataSet.moveNext();
</SCRIPT>

<SPAN DATASRC="#data1" DATAFLD="name"></SPAN>

<SPAN DATASRC="#data1" DATAFLD="age"></SPAN>

Now, the output will be: Vinod 18

The above script is fairly self explanatory. Initially we store the entire data of the data file in a variable dataset using the recordset method. The moveNext() method points to the next data item (next row). Some of other methods that can be used are:

·moveFirst() - Point to the first data item (first row)

·moveLast() - Point to the last data item (last row)

·EOF - This property is used to check whether we've reached the end of the file.

Now, I'll wrap up this article with a more dynamic example. I'll create a JavaScript Ticker that displays a number of messages with each message pointing to a particular URL. Here, the ticker will read its messages and the corresponding URL from a text file (tickerData.txt from the archive). For a full understanding of this code, you must be familiar with dynamic HTML techniques.

Here's the tickerData.txt file:

~message~|~messageURL~
~SitePoint.com~|~http://www.sitepoint.com~
~WebmasterBase~|http://www.webmasterbase.com~
~BBC News~|http://www.bbc.co.uk~

And the tickerStyle.css file:

.tickerStyle{font-family:verdana,arial,helvetica; color:#666699;
font-weight:bold; font-size:8pt; background:#EEEEFF;
border-right:#666699 solid 2px; border-left:#666699 solid 1px;
border-top:#666699 solid 1px; border-bottom:#666699 solid 2px;
padding:3px; width:400px; text-align:center; text-decoration:none}

.tickerStyle:hover{font-family:verdana,arial,helvetica;
color:#666699; font-weight:bold; font-size:8pt; background:#DDDDEE;
border-right:#666699 solid 1px; border-left:#666699 solid 2px;
border-top:#666699 solid 2px; border-bottom:#666699 solid 1px;
padding:3px; width:400px; text-align:center; text-decoration:none}

And lastly, ticker.htm:

<html>
<head>
<title>JavaScript Ticker (using Tabular Data Control)</title>
<link rel="stylesheet" href="tickerStyle.css">
<script language="JavaScript">
// JavaScript Ticker
// - using Tabular Data Control
// By Premshree Pillai

/*
The Ticker function
objName : the ID of the object to be used as data source
maxMsgs : the number of messages in the data file
counter : to keep count of the messages
timeOut : delay (in milliseconds)
*/

function TDC_Ticker(objName, counter, maxMsgs, timeOut)
{
try
{
eval('tickerSet=' + objName + '.recordset');
if(!tickerSet.EOF && counter<maxMsgs-1)
{
tickerSet.MoveNext();
counter++;
}
else
{
counter=0;
tickerSet.MoveFirst();
}
setTimeout("TDC_Ticker('"+objName+"','"+counter+"',
'"+maxMsgs+"','"+timeOut+"')", timeOut);
}
catch(e)
{
alert('This Ticker works with IE 4+ only.');
}
}
</script>

</head>
<body bgcolor="#FFFFFF">


<center>
<object id="ticker" classid="CLSID:333C7BC4-460F-11D0-BC04-0080C7055A83">
<param name="DataURL" value="tickerData.txt">
<param name="UseHeader" value="TRUE">
<param name="TextQualifier" value="~">
<param name="FieldDelim" value="|">
</object>
<a href="" datasrc="#ticker" datafld="messageURL" class="tickerStyle">
<span id="tickerDiv" datasrc="#ticker" datafld="message"></span>
</a>
<script language="JavaScript">
var tickerMaxMsgs=3; // Maximum Messages in the Data File
var tickerCount=tickerMaxMsgs;
new TDC_Ticker('ticker',tickerCount,tickerMaxMsgs,2000); // Set the Ticker
</script>
</center>


</body>
</html>

本文地址：http://com.8s8s.com/it/it29045.htm