On May 26, 2009, at 4:36 PM, Bill Steele wrote:

> For applications that don't enable UI events it is apparently  
> possible to get System Events to click a button by giving it the XY  
> coordinates.
>
> OK, coordinates from where?  The top corner of the app's window,   
> the position on the entire screen?
> In the former case, how do we find the exact position of, say, a  
> radio button other than looking at the app's source code?
>
> I've been poking around the web for sample System Events code and  
> all I've found so far are articles saying that you can do this or  
> that with System Events, isn't that handy?

It isn't quite clear what you're asking, but I'll try to help you out.

When you refer to applications that "don't enable UI events," do you  
mean applications that don't support AppleScript? If so, yes, you can  
use Apple's System Events application, which is built in to Mac OS X,  
to control user interface elements like buttons. This only works if  
you first turn on the "Enable access for assistive devices" setting in  
the Universal Access pane of System Preferences.

The technology for doing this is called "GUI Scripting," and it works  
by sending AppleScript commands to the System Events application. That  
application implements a bunch of AppleScript commands that know how  
to control the user interface elements in running processes. One of  
those commands is called 'click.' One of the parameters of the 'click'  
command is 'at.' According to the System Events application's  
AppleScript terminology dictionary, when you use the AppleScript GUI  
Scripting command 'click at', you should use "the { x, y } location at  
which to click, in global coordinates." This means you should use the  
screen coordinates, where the origin {0, 0} is at the bottom left  
corner of your main screen.

The only way to know where a button is located is to ask the  
application that owns the button where it is right now. Application  
windows can be moved around, and only the application knows where a  
button in one of its windows is currently located. You can find this  
out with GUI Scripting by asking the System Events application to tell  
you where the target application's window is currently located, and  
where in that window the button is located. Then you can convert that  
location to the global coordinates of the button and use the 'click  
at' command.

But it is much easier to just use GUI Scripting to tell the target  
application to 'click' the button. All that the 'click at' command  
does is to find the button that is located there, then send it the  
'click' command. You might as well short-circuit the process by  
telling System Events to tell the target application process to  
'click' the button.

If you don't already know anything about GUI Scripting, you didn't  
understand what I just wrote, so you have to do some studying. One way  
to start is to download the free 30-day trial version of my  
application "PreFab UI Browser." Its help files contain a lot of  
information about GUI Scripting, and it helps you compose AppleScript  
commands directed to the System Events application.

--

Bill Cheeseman - [log in to unmask]
Quechee Software, Quechee, Vermont, USA
www.quecheesoftware.com

PreFab Software - www.prefabsoftware.com