Thursday, June 18, 2009

when would table model data change show up (TableModel/EDT fusing)

Q: If on a non-EDT thread, such as a market data thread, I modify the table model beneath a "showing" ("realized") jtable, say change text from "A" to "B", but don't repaint or fire table change event, when will my new text show up on screen?

A: never. I tested with a custom table model. The new text shows up only after I repaint or fire table event.

A: you must send an invitation to the EDT to re-query the table model and then repaint the visual, otherwise the visual will not update. Look at INotifyPropertyChanged in wpf.

A (from a veteran): For custom table model, we need to fire events, either cell change event or table data change event.
A (from a veteran, echoed on http://stackoverflow.com/questions/3179136/jtable-how-to-refresh-table-model-after-insert-delete-or-update-the-data): in some cases like default table model setValueAt()/addRow(), the event is fired automatically. I'd say the more common and standard procedure is to always fire events manually

Q: Will firing event involve repaint()?
A: not according to my debug test

Q: will firing the event trigger paint()?
A: yes according to my debug test. EDT runs paint().

Q2: is it safe for non-EDT thread to make state change on the table model object?
A: not sure. The only way to propagate the state change to the screen is via native screen object.
There are perhaps 4 (or more) objects involved:
- JTable instance (view-controller?)
- Model instance
- ?UI delegate object
- native screen object

We are modifying the model object, not the "real" object (whatever it is), so screen won't update. UI delegate or native screen object are probably not directly accessible.

http://docs.oracle.com/javase/6/docs/api/javax/swing/package-summary.html#threading says "This restriction also applies to models attached to Swing components. For example, if a TableModel is attached to a JTable, the TableModel should only be modified on the event dispatching thread. If you modify the model on a separate thread you run the risk of exceptions and possible display corruption." This seems to suggest that TableModel objects are modified by even handlers due to user actions or due to timers ...

Q: when user edits a table cell, does the table model object change via an event callback or automatically without any event callback?
A: via Event callback, on EDT. My debug test show stopCellEditing(..) is invoked by Hollywood. This indirectly calls editingStopped(...), which calls setValueAt(..)

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