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Thread: Running VariableChange Events

  1. #1
    Join Date
    21.02.2019
    Posts
    3

    Default Running VariableChange Events

    [Zenon Editor 6.51]

    I have a problem when I call a function from a VariableChange Event;

    The function I'm calling executed a CMD prompt to start a f.t.p. download. This process takes a few seconds to complete.
    And thus the function has to wait (while loop) for it's result to show back to the runtime.

    Calling this function via an object element (e.g. button) allows the runtime to continue running properly.
    But when this function is called via the VariableChange the runtime freezes for that duration.

    It seems like functions executed via an element runs like a backgroundtask (no GUI interrupt) and function executed via VariableChange runs like forgroundtask (GUI interrupt).
    Am I correct in this assumption and is there a way for the VariableChange event to be run like a background task, in other words not impede the runtime while executing?


    Many thanks (again) in advance,
    Mitchel

  2. #2

    Default Re: Running VariableChange Events

    Hi Mitchel,

    You are correct in your assumption, that anything executed in event handlers of the API is blocking the main execution of the runtime. Any action that requires more time should therefore be executed in its own thread. Unfortunately, VBA is not suited for this task as it does not support multi-threading in this sense. What you could do, is set a variable value to "1" in the change event and react to the value "1" with a regular limit that executes a zenon function.

    Note, that a function that executes a VBA macro which requires more time to complete, does not directly block the main execution of the runtime, but it will block other functions in the same function queue.

    In newer versions, the zenon logic runtime provides function blocks to act as an FTP client.

    Best regards,
    Mark

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