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The table view does a number of things to improve performance as much as possible. As a result, if you just change values in the datasource without telling it, it won’t know that something has changed. In our case, we added a new value to the array used by our datasource but didn’t let the table view know about it.
Since we’re modifying the underlying data used by the datasource, the easiest way to refresh the table is to ask it to reload its data. You do this by sending it the reloadData message. This tells the tableview to reconstruct everything—how many sections it thinks it has, the headers and footers of those sections, its data rows, etc.