how to set textbox control is editable and non editable

Question

how to set textbox control is editable and non editable in the page load  

 for example::

if txtname.text.trim().length >0

{

txtname.readonly=false;

 

} 

else

{

 txtname.readonly=true;

} 

 

Plz Help  me as early as possiable .... urgent guyss help me