Question

AppleScript’s list data type has only a very limited support for boolean test specifiers. Besides picking items by range (with the item keyword), specifying a class will work:

get every «class furl» of {1, "Test", (POSIX file "/posix/path")} --> {file ":hfs:path"} 

When the list items are references, dereferencing with the contents keyword will work:

get every «class furl» of {1, "Test", a reference to (POSIX file "/posix/path")} --> {}
get every «class furl» of contents of {1, "Test", a reference to (POSIX file "/posix/path")} --> {file ":hfs:path"}

So why does the following code set allTextAreas to an empty list:

tell application "System Events"
    set allUIElements to entire contents of window 1 of someApplication 
    set allTextAreas to every text area of contents of allUIElements --> {}
end tell

given that allUIElements is a list of references to UI element objects, and that at least one of them is of class text area?

Note I am not looking for suggestions how to retrieve all UI elements of a certain type from the list (a repeat loop will do that) – I would like to understand why the selector pattern fails in this specific case.

Answer 1

Getting the UI elements from the application results in a list of object specifiers: application objects (a form of nested containers) where each item in the hierarchy has several properties, including a class – Technical Note TN2106 might shed more light on this –, while your first example used a file URL (a type of file reference) which has a base class.

So you will need to use either an application filter reference form when getting the objects from the application or query the desired properties of the returned objects, for example:

set allButtons to {}
tell application "System Events" to tell application process "Safari"
    set allUIElements to entire contents of window 1
    repeat with anElement in allUIElements
        try
            if class of anElement is button then set end of allButtons to contents of anElement
        end try
    end repeat
end tell
allButtons