Yield PowerScript function
Description
Yields control to other graphic objects, including objects
that are not PowerBuilder objects. Yield checks
the message queue and if there are messages in the queue, it pulls
them from the queue.
Syntax
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<span>Yield</span> ( ) |
Return Values
Boolean. Returns true if
it pulls messages from the message queue and false if there
are no messages.
Usage
Include Yield within a loop so that other
processes can happen. For example, use Yield to
allow end users to interrupt a loop. By yielding control, you allow the
user time to click on a cancel button in another window. Then code
in the loop can check whether a global variable’s status
has changed. You can also use Yield in a loop
in which you are waiting for something to finish so that other processing
can take place, in either your or some other application.
Using other applications while retrieving data
Although the user cannot do other activities in a PowerBuilder
application while retrieving data, you can allow them to use other
applications on their system. Put Yield in the
RetrieveRow event so that other applications can run during the
retrieval.
Of course, Yield will make your PowerBuilder
application run slower because processing time will be shared with
other applications.
Examples
In this example, some code is processing a long task.
A second window includes a button that the user can click to interrupt
the loop by setting a shared boolean variable sb_interrupt.
When the user clicks the button, its Clicked script sets sb_interrupt,
shown here:
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sb_interrupt = TRUE |
The script that is doing the processing checks the
shared variable sb_interrupt and interrupts
the processing if it is true. The Yield function
allows a break in the processing so the user has the opportunity
to click the button:
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integer n |
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// sb_interrupt is a shared variable. |
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sb_interrupt = FALSE |
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FOR n = 1 to 3000 |
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<span> Yield</span>() |
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IF sb_interrupt THEN // var set in other script |
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MessageBox("Debug","Interrupted!") |
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sb_interrupt = FALSE |
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EXIT |
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ELSE |
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... // Some processing |
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END IF |
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NEXT |
In this example, this script doing some processing
runs in one window while users interact with controls in a second
window. Without Yield, users could click in the
second window, but they would not see focus change or their actions
processed until the loop completed:
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integer n |
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FOR n = 1 to 3000 |
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<span> Yield</span>() |
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... // Some processing |
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NEXT |
In this example, a script wants to open a DDE channel
with Lotus Notes, whose executable name is stored in the variable
mailprogram. If the program is not running, the script starts it
and loops, waiting until the program’s startup is finished
and it can establish a DDE channel. The loop includes Yield,
so that the computer can spend time actually starting the other
program:
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time starttime |
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long hndl |
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SetPointer(HourGlass!) |
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//Try to establish a handle; SendMail is the topic. |
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hndl = OpenChannel("Notes","SendMail") |
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//If the program is not running, start it |
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IF hndl < 1 then |
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Run(mailprogram, Minimized!) |
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starttime = Now() |
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// Wait up to 2 minutes for Notes to load |
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// and the user to log on. |
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DO |
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//Yield control occasionally. |
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<span> Yield</span>() |
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//Is Notes active yet? |
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hndl = OpenChannel("Notes","SendMail") |
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// If Notes is active. |
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IF hndl > 0 THEN EXIT |
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LOOP Until SecondsAfter(StartTime,Now()) > 120 |
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// If 2 minutes pass without opening a channel |
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IF hndl < 1 THEN |
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MessageBox("Error", & |
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"Can't start Notes.", StopSign!) |
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SetPointer(Arrow!) |
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RETURN |
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END IF |
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END IF |