Can placeholder address as readonly?

my usercontrol(.ascx) marked as readonly?
By this I assume that you want to make your usercontrol readonly because you don't want any modification on your controls? Why not create your own Readonly property on your user control, like this?

public bool ReadOnly
{
   get
   {
      return readOnly_var; //here you return the initial value of your property that is stored somewhere
   }
   set
   {
      TextBox1.ReadOnly = value;
      //etc... put the controls that you want to be readonly
   }
}

And then on your page, you can set the property like this.

UserControl1.ReadOnly = true;