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Since this process won't do anything other than loop through the records (the XML export that inspired the original procedure is outside the scope of this article) all I'm doing is displaying the current record on screen. 

Setting up for sequential processing

When the window opens up, any timer event code will execute because I had to set a Timer attribute on my window in order to get the Event:Timer embed point. So I need to disable the timer. Right after Self.Open(WINDOW) I add this code:

    0{prop:timer} = 0  

The value of 0 before the property assignment means I am assigning to the currently active window. I could also use 

    Window{prop:timer} = 0  

but "0" takes less typing. And if you're ever writing code that needs to apply generically to a window using 0 means you don't need to know the window label. 

I have a little more setup code that executes around the same time (actually just before opening the window):

    FirstPeopleID = PEO:ID
    clear(PEO:ID,1)
    set(PEO:KeyId,PEO:KeyId)
    previous(people)
    if errorcode() 
        LastPeopleID = 0
    else
        LastPeopleID = PEO:Id
    end
    clear(PEO:RECORD)

This code:

• assumes the first record I want to process is in memory, and saves the ID of that record in FirstPeopleID
• primes LastPeopleID with the hightest ID in the file 
• clears the record so nothing displays when the window first opens

Using timer events

I'm going to use a timer event to step through the records I need to process. This is typically how Clarion reports and processes work,  - by processing a set number of records on each timer event the UI can remain relatively responsive and react to cancellation requests. 

The Event:Timer embed point only appears when the window has a Timer attribute, so be sure to set that value. Any non-zero value will do. 

Here's the Event:Timer code:

        next(People)
        if errorcode() or PEO:Id > LastPeopleID 
            0{prop:timer} = 0
            post(event:closewindow)
        else
            ?Progress{PROP:Progress} = PEO:Id
        end

When the start button is clicked this code executes:

        TimerInterval = 50
        PEO:Id = FirstPeopleID
        set(PEO:KeyId,PEO:KeyId)
        0{prop:timer} = TimerInterval
        ?Progress{PROP:RangeLow} = FirstPeopleID 
        ?Progress{PROP:RangeHigh} = LastPeopleID
        disable(?StartButton)
        enable(?PauseButton)

First I set a local variable which is the value that will be applied to Prop:Timer. There are two places this happens (as you'll see); I use a local variable so that if I want to change the value I only need to do so in one place. A value of 50 means the timer will execute every half second, which is probably a lot less frequent than I'd really want it to happen but it allows the process to at a good demonstration speed. A common technique, and the one Clarion apps use, by default, is to process a fixed number of records for each timer event.