[vwnc] Fundamental flaw in Wrapper architecture

I made a simple modification to the File browser that uses a dataset

in place of the file list. This would permit me to see file dates and sizes

in addition to the file name. Additionally, the dataset is able to sort on a

selected column, which I find rather helpful when there are a lot of files.

The problem I encountered was when I removed a file. Due to the

“unsynchronous” nature of the Wrapper architecture the dataset

attempted to display the file that was just removed. One can easily

reproduce this simply by changing AbstractFileItem>>displayString

to the following and then remove a file, no other changes to the

FileBrowser are necessary.

displayString

            ^filename tail , ' - ' , filename modificationTimestamp printString

The actual problem I encountered is a little more complex because I am

using a modified Aragon dataset. In this situation the dataset’s ‘model’

and ‘sequence’ are different objects because, in the general case, when

a sorted list is presented the model’s list should not be reordered.

I say that the architecture is flawed because change/update mechanism

in concert with #invalidateNow causes the system to attempt to redisplay

portions of the application before all the underlying objects have been

updated to reflect the new state. I say “underlying objects” rather than the

model because the various views and widgets may also have supporting

objects, i.e. a sorted list, that must be updated to display properly.

I suggest that eliminating all immediate display updates would be the

first step in correcting this problem.

Terry

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Terry Raymond
Crafted Smalltalk
80 Lazywood Ln.
Tiverton, RI  02878
(401) 624-4517      [hidden email]
<http://www.craftedsmalltalk.com>
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