Question

As you can see, if the condition is true, I attempt to use substring command to get 20 character. But it doesn’t agree.

'<%#IIf(Eval("haber").ToString().Length >= 20, Eval("haber").ToString().Substring(0, 20) + "...", Eval("haber").ToString )%>'

Also, I’m using that code on onmouseover event.

Like this:

<a href="" onmouseover=""/>

What might be the problem?

Answer 1

First of all: move your logic from markup to the method at codebehind and call this method in markup.

Markup:

<%# this.FormatValue(Eval("haber")) %>

Codebehind:

public string FormatValue(object value)
{
    string str = (string)value;

   if (str.length > 20)
     return str.Substring(0, 20) + "...";

   return str;
} 

Second: you have syntax error in your expression: in the last ToString missing ()