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ASP.NET Client Side Focus Helper

, 19 Jan 2004
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Helper class that generates and registers a client side script which sets focus to a control during the loading of the page.

Sample Image - ClientSideFocus.jpg

Introduction

I've been working on trying to set the focus of client side controls today and thought I'd submit this as I think it could be useful. I hope I haven't missed a method that is already built into ASP.NET that already does this.

I've created a helper class that enables you to set the client side focus with a single call. I decided against creating a subclass of the Page class as I think the helper class approach is better and easier to implement on existing systems.

How it worked originally

All that is required is the ID of the form which the control is in and the ID of the control itself. There are a couple of overloaded functions that automatically find these IDs depending on what type of server control you pass as a parameter.

private void Page_Load(object sender, System.EventArgs e)
{
  if( !this.IsPostBack )
  {
    McGiv.Web.UI.ClientSideFocus.setFocus(this.TextBox1);
    this.ViewState["focus"] = "WebControl";
  }
}

The JavaScript script is then generated and registered to the given Page object.

The script itself makes a copy of the document.body.onload function and replaces it with the focus setting function which in turn calls the original onload function, which means that you won't have to tinker with any existing onload scripts you may have within your pages.

// save original function
 if(document.body.onload)
  original = document.body.onload;

 // override original function
 document.body.onload = document_onLoad;

 function document_onLoad()
 {
  try
  {
   document.FormID.ControlID.focus();
  }
  catch(e){}

  // call original function
  original();
 }


 function original()
 {
  // do nothing if original is null
 }

How it works now

After being notified that the original code could potentially steal the focus of another window (which can be irritating), I switched from using the document.body.onload event to the document.body.onfocus event.

    var called = false;

    if(document.body.onfocus)
        orig_document_body_onfocus = document.body.onfocus;

    document.body.onfocus = document_body_onfocus;


    function setFocus()
    {
        var control = document.getElementById("html");
        if(control)
            control.focus();
    }


    function orig_document_body_onfocus(){}
    
    function document_body_onfocus ()
    {
        if( !called )
        {
            called = true;
            setFocus();
        }

        orig_document_body_onfocus();
    }



    if( window.__smartNav && window.__smartNav.restoreFocus)
    {
        orig_window__smartNav_restoreFocus = window.__smartNav.restoreFocus;
        window.__smartNav.restoreFocus = window__smartNav_restoreFocus;
    }


    function orig_window__smartNav_restoreFocus(){}

    function window__smartNav_restoreFocus()
    {
        setFocus();
        orig_window__smartNav_restoreFocus
    }

I’ve also tried to solve the problem with Smart Navigation by overriding the restoreFocus function from within SmartNav.js file but this seems to only work on my local machine at the moment. This may be due to a security issue or due to the loading time taken from remote hosts.

I removed the need for the ID of the HTML form, as with most cases within ASP.NET, the page will only use one form. This modification alone removes about half the content from the original code. I’ve included the original code if you still need to reference the form's ID as well as the control ID.

Known Issues

Currently, the helper class doesn’t function properly when Smart Navigation is enabled.

The demo

I've included a simple demo that switches focus between a WebControl, HtmlControl and a hard coded HTML input control.

I use the viewstate to keep track of which control has focus.

private void Button1_Click(object sender, System.EventArgs e)
{
  string focus = this.ViewState["focus"] as string;
  if( focus == null )
    focus = "WebControl";
  switch(focus)
  {
    case "Html":
    {
      McGiv.Web.UI.ClientSideFocus.setFocus(this.TextBox1);
      this.ViewState["focus"] = "WebControl";
      break;
    }
    case "HtmlControl":
    {
      McGiv.Web.UI.ClientSideFocus.setFocus(this, "html");
      this.ViewState["focus"] = "Html";
      break;
    }
    case "WebControl":
    {
      McGiv.Web.UI.ClientSideFocus.setFocus(this.HtmlControl1);
      this.ViewState["focus"] = "HtmlControl";
      break;
    }
  }
}

In order to get it to work, unzip the demo files into a virtual directory mapped to http://localhost/ClientSideFocus/.

I've also setup an online demo here.

Enjoy.

Version History

  • Version 1.3: Wednesday 21 Jan 2003
    • Fixed null object JavaScript bug.
  • Version 1.2: Tuesday 20 Jan 2003
    • Moved the call to setFocus from the document.body.onload event to the document.body.onfocus event. This stops the focus being taken from another browser window that has the focus.
    • Discovered that the code only works with Smart Navigation on my local machine & not my remote host. Don't know if this is a security issue or a loading time issue.
  • Version 1.1: Wednesday 14 Jan 2003
    • Removed script from onload event. Allows it to work with Mozilla browsers too.
    • Used getElementById([control name]) instead of using [form name].[control name].
    • Removed need to search for form's ID - with ASP.NET, only 1 form is used normally removing the need to supply the form ID.
    • Overrides restoreFocus Smart Navigation function. Now works when smart navigation is enabled.
  • Version 1.0: Tuesday 13 Jan 2003
    • Will function if Smart Navigation is enabled on the WebForm. Only tested on IE 6.1.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

McGiv
Web Developer
United Kingdom United Kingdom
I'm a 3rd year student at Uni studing Computing. I've been coding in VB for about 6 years, Java for about 3 and C# for about 2 years.

Comments and Discussions

 
GeneralMinor Change... PinmemberJaben C12-Oct-04 3:40 
GeneralRe: Minor Change... PinmemberMcGiv12-Oct-04 3:46 

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