Hi TS,
Your understanding is correct. By using writer.AddAttribute we cannot
guarantee the attribute we add is visible in the DOM. Here's a sample. You
can test it in IE 8 and FireFox. The result may be different. In IE 8 you
will see "testvalue" after clicking the button. In FireFox you may see
"undefined".
Aspx.cs:
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
MyTextBox t = new MyTextBox();
this.form1.Controls.Add(t);
ClientScript.RegisterStartupScript(this.GetType(), "key",
@"<script type=""text/javascript"">
function Test() {
var test=document.getElementById('" + t.ClientID +
"').testkey;alert(test);}</script>");
}
}
public class MyTextBox : TextBox {
public override void RenderBeginTag(HtmlTextWriter writer)
{
writer.AddAttribute("testkey", "testvalue");
base.RenderBeginTag(writer);
}
}
Aspx:
<input type="button" onclick="Test()" value="Click Me" />
If you try the following code instead, you will see "testvalue" in FireFox
as well:
public class MyTextBox : TextBox {
public override void RenderBeginTag(HtmlTextWriter writer)
{
Page.ClientScript.RegisterExpandoAttribute(this.ClientID,
"testkey", "testvalue");
base.RenderBeginTag(writer);
}
}
This is because the RegisterExpandoAttribute method renders some
Javascript
code to add the attribute into the DOM directly. In a word it can give us
the guarantee that the custom attributes we add will be visible in the DOM
for all the browsers.
If the attribute is a standard attribute, however, you can just use
AddAttribute method. It's more efficient cause less data need to be
transmitted through the network.
To get the valid attributes list for a specifig tag please refer to:
http://www.w3schools.com/tags/default.asp
Regards,
Allen Chen
Microsoft Online Support
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