23.9. Observer/Publish-Subscribe/Delegation Event Model (GoF)
Another requirement for the iteration is adding the ability for a GUI window to refresh its display of the sale total when the total changes (see Figure 23.20). The idea is to solve the problem for this one case, and then in later iterations, extend the solution to refreshing the GUI display for other changing data as well.
Figure 23.20. Updating the interface when the sale total changes.
Why not do the following as a solution? When the Sale changes its total, the Sale object sends a message to a window, asking it to refresh its display.
To review, the Model-View Separation principle ...
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