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Support Article

Screen flow hangs when attachment is downloaded



When using the 'pega.ui.HarnessActions.doAttachmentSingleClick' script to download attachments that are present within a screen flow, the system stops processing. This occurs in the Case Worker portal.

Error Messages

Not Applicable

Steps to Reproduce

  1. Create a screen flow.
  2. Create an assignment with a section within the screen flow.
  3. Add a button to the assignment's section that invokes the 'pega.ui.HarnessActions.doAttachmentSingleClick' script upon a click.
  4. Execute the screen flow.
  5. Navigate the flow to the point where the button with the script was added.
  6. Click the button.
  7. Click 'Continue' or 'Finish' in the flow.

Root Cause

When an attachment is downloaded using the pega.ui.HarnessActions.doAttachmentSingleClick() script function, internally the ATTACHMENT-DATA iFrame is used. When iFrames are involved, the ChangeTracker is invoked to communicate the data between different iFrames.
The Case Worker portal is a single-thread model; while the Manager or the Admin portal are multi-threaded. In the Manager or the Admin portal, the ChangeTracker is invoked on the top level frame. As a result, the system works correctly.
However, for the Case Worker portal, the ChangeTracker is invoked on a dummy iFrame that is created for download (that is, ATTACHMENT-DATA). Since this is a dummy iFrame, the  ChangeTrackerMap object is not present. Hence, the script fails in the trackXThreadChanges script function and the screen freezes.


Perform the following local-change:
  1. Modify the DisplayAttachment HTML rule where the ChangeTrackerMap is built for the dummy iFrame.
  2. Add the below line of code in the HTML Rule,

    pega.ui.ChangeTrackerMap = {"getTracker":function(){}};

Published August 5, 2020 - Updated December 2, 2021

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