Graphical glitches when adding cells and scrolling with UITableView
- by Daniel I-S
I am using a UITableView to display the results of a series of calculations. When the user hits 'calculate', I wish to add the latest result to the screen. This is done by adding a new cell to a 'results' section. The UITableViewCell object is added to an array, and then I use the following code to add this new row to what is displayed on the screen:
[thisView beginUpdates];
[thisView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation: UITableViewRowAnimationFade];
[thisView endUpdates];
This results in the new cell being displayed. However, I then want to immediately scroll the screen down so that the new cell is the lowermost cell on-screen. I use the following code:
[thisView scrollToRowAtIndexPath:newIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
This almost works great. However, the first time a cell is added and scrolled to, it appears onscreen only briefly before vanishing. The view scrolls down to the correct place, but the cell is not there. Scrolling the view by hand until this invisible new cell's position is offscreen, then back again, causes the cell to appear - after which it behaves normally. This only happens the first time a cell is added; subsequent cells don't have this problem. It also happens regardless of the combination of scrollToRowAtIndexPath and insertRowsAtIndexPath animation settings.
There is also a problem where, if new cells are added repeatedly and quickly, the new cells stop 'connecting up'. The lowermost cell in a group is supposed to have rounded corners, and when a new cell is added these turn into square corners so that there is a clean join with the next cell in the group. In this case, however, a cell often does not lose its rounded edges despite not being the last cell anymore. This also gets corrected once the affected area moves offscreen and back.
This method of adding and scrolling would be perfect for my application if it weren't for these weird glitches. Any ideas as to what I may be doing wrong?
