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Using a timer

Looping through records in a tight loop with no possibility of interrupting the loop is almost never a good idea unless you are only dealing with a handful of records. Clarion reports and processes avoid this problem by using a window timer and looping through a smaller number of records on each timer event. In between these processing loops the UI can respond to user input. 

I'm going to use a similar approach, which means I need to be able to put code into the Event:Timer embed. And that embed only appears when the window has a Timer attribute. Any non-zero value will do. 

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 pointof that required Timer attribute. So I need to disable the timer. Right after Self.Open(WINDOW) I add this code:

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• 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 codeHere's the Event:Timer code (I'll explain the use of PROP:Progress in a moment):

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

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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. 

I'll also only be processing on record per timer event. 

I then do a Set in primary key order on the People file.

Displaying the progress bar

This is the bit I really like about this whole procedure. By default, progress bars have a range of values from 1 to 100, and if you want to use that range and you don't have exactly 100 records you need to do some math. 

?Progress{PROP:RangeLow} = FirstPeopleID 
?Progress{PROP:RangeHigh} = LastPeopleID

The RangeLow and RangeHigh properties let you set the lower and upper boundaries to whatever value you like. Because I'm setting the low value to the first primary key value, and the high value to the last primary key value, all I need to do to display the progress bar is set PROP:Progress to the current primary key value (as shown earlier):

?Progress{PROP:Progress} = PEO:Id

I'm not sure just how big RangeHigh can get, but I've tried it with the maximum LONG values and it still works, so if you're using LONGs for primary key values you needn't worry. 

Pause and Cancel

There are two more events I need to respond to: Pause and Cancel. 

The Cancel button code is simple - just disable the timer and post a CloseWindow event:

        0{prop:timer} = 0
        post(EVENT:CloseWindow)

The Pause button code is more elaborate, as I want to be able to toggle the button text between 'Pause' and 'Resume'. This is also the second place where I use the TimerInterval variable. 

        if ?PauseButton{prop:text} = 'Pause' 
            if 0{prop:timer} > 0
                0{prop:timer} = 0
                ?PauseButton{prop:text} = 'Resume'
            end
        else
            ?PauseButton{prop:text} = 'Pause'
            0{prop:timer} = TimerInterval
        end

Summary

Although I could have used a Process template in this situation, with relatively little code I have achieved the following:

• Easy selection of range limiting values
• Accurate progress bar display
• The ability to pause the process

This technique works best on sequentially numbered single component keys, such as primary keys, although with a bit of work you might be able to adapt it to other situations. 

And of course this was a one-off job; if I come across other places where I need something similar I'll look into creating a class and/or a template. But sometimes a little hand code goes a long way.